[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Trova bug sottili e spiega quali invarianti dell'inferenza possono rompersi.

File: ds4_metal.m

```c
sinks_offset,
                                                                         q,
                                                                         raw_kv,
                                                                         n_tokens,
                                                                         window,
                                                                         n_head,
                                                                         head_dim);
    }

    id<MTLBuffer> qbuf = ds4_gpu_tensor_buffer(q);
    id<MTLBuffer> rawbuf = ds4_gpu_tensor_buffer(raw_kv);
    id<MTLBuffer> headsbuf = ds4_gpu_tensor_buffer(heads);
    const uint64_t q_bytes = (uint64_t)n_tokens * n_head * head_dim * sizeof(float);
    const uint64_t raw_bytes = (uint64_t)n_tokens * head_dim * sizeof(float);
    if (!qbuf || !rawbuf || !headsbuf || !sinks_buf ||
        ds4_gpu_tensor_bytes(q) < q_bytes ||
        ds4_gpu_tensor_bytes(raw_kv) < raw_bytes ||
        ds4_gpu_tensor_bytes(heads) < q_bytes) {
        fprintf(stderr, "ds4: Metal prefill raw DS4 FlashAttention received undersized buffers\n");
        return 0;
    }

    const uint32_t ncpsg = 32;
    const uint32_t nwg = 32;
    const uint32_t nsg = ds4_gpu_flash_attn_vec_nsg(n_tokens, nwg, ncpsg);
    const NSUInteger row_bytes = (NSUInteger)head_dim * sizeof(float);
    const NSUInteger row_bytes_f16 = (NSUInteger)head_dim * sizeof(uint16_t);
    const NSUInteger mask_bytes = (NSUInteger)n_tokens * (NSUInteger)n_tokens * sizeof(uint16_t);
    const NSUInteger kv_f16_offset = 0;
    const NSUInteger kv_f16_bytes = (NSUInteger)n_tokens * row_bytes_f16;
    const NSUInteger pad_bytes = 2u * (NSUInteger)ncpsg * row_bytes_f16 +
                                 (NSUInteger)ncpsg * (NSUInteger)n_tokens * sizeof(uint16_t);
    const NSUInteger nrows = (NSUInteger)n_tokens * n_head;
    const NSUInteger tmp_bytes = nrows * (NSUInteger)head_dim * (NSUInteger)nwg * sizeof(float) +
                                 nrows * (2u * (NSUInteger)nwg) * sizeof(float);

    id<MTLBuffer> mask_buffer =
        ds4_gpu_new_transient_buffer(mask_bytes, "ds4_flash_attn_mask");
    if (!mask_buffer ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_pad_buffer,
                                         &g_flash_attn_pad_bytes,
                                         pad_bytes,
                                         "ds4_flash_attn_pad") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_kv_buffer,
                                         &g_flash_attn_kv_bytes,
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Trova bug sottili e spiega quali invarianti dell'inferenza possono rompersi.

File: ds4_metal.m

```c
sinks_offset,
                                                                         q,
                                                                         raw_kv,
                                                                         n_tokens,
                                                                         window,
                                                                         n_head,
                                                                         head_dim);
    }

    id<MTLBuffer> qbuf = ds4_gpu_tensor_buffer(q);
    id<MTLBuffer> rawbuf = ds4_gpu_tensor_buffer(raw_kv);
    id<MTLBuffer> headsbuf = ds4_gpu_tensor_buffer(heads);
    const uint64_t q_bytes = (uint64_t)n_tokens * n_head * head_dim * sizeof(float);
    const uint64_t raw_bytes = (uint64_t)n_tokens * head_dim * sizeof(float);
    if (!qbuf || !rawbuf || !headsbuf || !sinks_buf ||
        ds4_gpu_tensor_bytes(q) < q_bytes ||
        ds4_gpu_tensor_bytes(raw_kv) < raw_bytes ||
        ds4_gpu_tensor_bytes(heads) < q_bytes) {
        fprintf(stderr, "ds4: Metal prefill raw DS4 FlashAttention received undersized buffers\n");
        return 0;
    }

    const uint32_t ncpsg = 32;
    const uint32_t nwg = 32;
    const uint32_t nsg = ds4_gpu_flash_attn_vec_nsg(n_tokens, nwg, ncpsg);
    const NSUInteger row_bytes = (NSUInteger)head_dim * sizeof(float);
    const NSUInteger row_bytes_f16 = (NSUInteger)head_dim * sizeof(uint16_t);
    const NSUInteger mask_bytes = (NSUInteger)n_tokens * (NSUInteger)n_tokens * sizeof(uint16_t);
    const NSUInteger kv_f16_offset = 0;
    const NSUInteger kv_f16_bytes = (NSUInteger)n_tokens * row_bytes_f16;
    const NSUInteger pad_bytes = 2u * (NSUInteger)ncpsg * row_bytes_f16 +
                                 (NSUInteger)ncpsg * (NSUInteger)n_tokens * sizeof(uint16_t);
    const NSUInteger nrows = (NSUInteger)n_tokens * n_head;
    const NSUInteger tmp_bytes = nrows * (NSUInteger)head_dim * (NSUInteger)nwg * sizeof(float) +
                                 nrows * (2u * (NSUInteger)nwg) * sizeof(float);

    id<MTLBuffer> mask_buffer =
        ds4_gpu_new_transient_buffer(mask_bytes, "ds4_flash_attn_mask");
    if (!mask_buffer ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_pad_buffer,
                                         &g_flash_attn_pad_bytes,
                                         pad_bytes,
                                         "ds4_flash_attn_pad") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_kv_buffer,
                                         &g_flash_attn_kv_bytes,
```<｜Assistant｜><think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Review this excerpt for correctness risks, memory lifetime issues, and performance bottlenecks.

File: ds4_metal.m

```c
"ds4_flash_attn_pad") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_kv_buffer,
                                         &g_flash_attn_kv_bytes,
                                         kv_f16_bytes,
                                         "ds4_flash_attn_kv_f16") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_tmp_buffer,
                                         &g_flash_attn_tmp_bytes,
                                         tmp_bytes,
                                         "ds4_flash_attn_tmp")) {
        return 0;
    }
    ds4_gpu_fill_raw_prefill_mask((uint16_t *)[mask_buffer contents], n_tokens, window);

    id<MTLComputePipelineState> pad_pipeline = nil;
    if ((n_tokens % ncpsg) != 0) {
        pad_pipeline = ds4_gpu_get_flash_attn_pad_pipeline(true, (int32_t)ncpsg);
        if (!pad_pipeline) return 0;
    }
    id<MTLComputePipelineState> vec_pipeline =
        ds4_gpu_get_flash_attn_vec_pipeline("kernel_flash_attn_ext_vec_f16_dk512_dv512",
                                              true, true, false, false, true,
                                              (int32_t)head_dim,
                                              (int32_t)head_dim,
                                              (int32_t)nsg,
                                              (int32_t)nwg);
    id<MTLComputePipelineState> reduce_pipeline =
        ds4_gpu_get_flash_attn_reduce_pipeline((int32_t)head_dim, (int32_t)nwg);
    if (!vec_pipeline || !reduce_pipeline) return 0;

    if (!ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                         rawbuf,
                                         ds4_gpu_tensor_offset(raw_kv),
                                         g_flash_attn_kv_buffer,
                                         kv_f16_offset,
                                         n_tokens * head_dim)) {
        return 0;
    }

    if ((n_tokens % ncpsg) != 0) {
        ds4_gpu_flash_attn_pad_args pad_args = {
            .ne11 = (int32_t)n_tokens,
            .ne_12_2 = 1,
            .ne_12_3 = 1,
            .nb11 = row_bytes_f16,
            .nb12 = (uint64_t)n_tokens * row_bytes_f16,
            .nb13 = (uint64_t)n_tokens * row_bytes_f16,
            .nb21 = row_bytes_f16,
            .nb22 = (uint64_t)n_tokens * row_bytes_f16,
            .nb23 = (uint64_t)n_tokens * row_bytes_f16,
            .ne31 = (int32_t)n_tokens,
            .ne32 = 1,
            .ne33 = 1,
            .nb31 = (uint64_t)n_tokens * sizeof(uint16_t),
            .nb32 = mask_bytes,
            .nb33 = mask_bytes,
        };
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Review this excerpt for correctness risks, memory lifetime issues, and performance bottlenecks.

File: ds4_metal.m

```c
"ds4_flash_attn_pad") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_kv_buffer,
                                         &g_flash_attn_kv_bytes,
                                         kv_f16_bytes,
                                         "ds4_flash_attn_kv_f16") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_tmp_buffer,
                                         &g_flash_attn_tmp_bytes,
                                         tmp_bytes,
                                         "ds4_flash_attn_tmp")) {
        return 0;
    }
    ds4_gpu_fill_raw_prefill_mask((uint16_t *)[mask_buffer contents], n_tokens, window);

    id<MTLComputePipelineState> pad_pipeline = nil;
    if ((n_tokens % ncpsg) != 0) {
        pad_pipeline = ds4_gpu_get_flash_attn_pad_pipeline(true, (int32_t)ncpsg);
        if (!pad_pipeline) return 0;
    }
    id<MTLComputePipelineState> vec_pipeline =
        ds4_gpu_get_flash_attn_vec_pipeline("kernel_flash_attn_ext_vec_f16_dk512_dv512",
                                              true, true, false, false, true,
                                              (int32_t)head_dim,
                                              (int32_t)head_dim,
                                              (int32_t)nsg,
                                              (int32_t)nwg);
    id<MTLComputePipelineState> reduce_pipeline =
        ds4_gpu_get_flash_attn_reduce_pipeline((int32_t)head_dim, (int32_t)nwg);
    if (!vec_pipeline || !reduce_pipeline) return 0;

    if (!ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                         rawbuf,
                                         ds4_gpu_tensor_offset(raw_kv),
                                         g_flash_attn_kv_buffer,
                                         kv_f16_offset,
                                         n_tokens * head_dim)) {
        return 0;
    }

    if ((n_tokens % ncpsg) != 0) {
        ds4_gpu_flash_attn_pad_args pad_args = {
            .ne11 = (int32_t)n_tokens,
            .ne_12_2 = 1,
            .ne_12_3 = 1,
            .nb11 = row_bytes_f16,
            .nb12 = (uint64_t)n_tokens * row_bytes_f16,
            .nb13 = (uint64_t)n_tokens * row_bytes_f16,
            .nb21 = row_bytes_f16,
            .nb22 = (uint64_t)n_tokens * row_bytes_f16,
            .nb23 = (uint64_t)n_tokens * row_bytes_f16,
            .ne31 = (int32_t)n_tokens,
            .ne32 = 1,
            .ne33 = 1,
            .nb31 = (uint64_t)n_tokens * sizeof(uint16_t),
            .nb32 = mask_bytes,
            .nb33 = mask_bytes,
        };
```<｜Assistant｜></think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Review this excerpt for correctness risks, memory lifetime issues, and performance bottlenecks.

File: ds4_metal.m

```c
"ds4_flash_attn_pad") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_kv_buffer,
                                         &g_flash_attn_kv_bytes,
                                         kv_f16_bytes,
                                         "ds4_flash_attn_kv_f16") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_tmp_buffer,
                                         &g_flash_attn_tmp_bytes,
                                         tmp_bytes,
                                         "ds4_flash_attn_tmp")) {
        return 0;
    }
    ds4_gpu_fill_raw_prefill_mask((uint16_t *)[mask_buffer contents], n_tokens, window);

    id<MTLComputePipelineState> pad_pipeline = nil;
    if ((n_tokens % ncpsg) != 0) {
        pad_pipeline = ds4_gpu_get_flash_attn_pad_pipeline(true, (int32_t)ncpsg);
        if (!pad_pipeline) return 0;
    }
    id<MTLComputePipelineState> vec_pipeline =
        ds4_gpu_get_flash_attn_vec_pipeline("kernel_flash_attn_ext_vec_f16_dk512_dv512",
                                              true, true, false, false, true,
                                              (int32_t)head_dim,
                                              (int32_t)head_dim,
                                              (int32_t)nsg,
                                              (int32_t)nwg);
    id<MTLComputePipelineState> reduce_pipeline =
        ds4_gpu_get_flash_attn_reduce_pipeline((int32_t)head_dim, (int32_t)nwg);
    if (!vec_pipeline || !reduce_pipeline) return 0;

    if (!ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                         rawbuf,
                                         ds4_gpu_tensor_offset(raw_kv),
                                         g_flash_attn_kv_buffer,
                                         kv_f16_offset,
                                         n_tokens * head_dim)) {
        return 0;
    }

    if ((n_tokens % ncpsg) != 0) {
        ds4_gpu_flash_attn_pad_args pad_args = {
            .ne11 = (int32_t)n_tokens,
            .ne_12_2 = 1,
            .ne_12_3 = 1,
            .nb11 = row_bytes_f16,
            .nb12 = (uint64_t)n_tokens * row_bytes_f16,
            .nb13 = (uint64_t)n_tokens * row_bytes_f16,
            .nb21 = row_bytes_f16,
            .nb22 = (uint64_t)n_tokens * row_bytes_f16,
            .nb23 = (uint64_t)n_tokens * row_bytes_f16,
            .ne31 = (int32_t)n_tokens,
            .ne32 = 1,
            .ne33 = 1,
            .nb31 = (uint64_t)n_tokens * sizeof(uint16_t),
            .nb32 = mask_bytes,
            .nb33 = mask_bytes,
        };
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Review this excerpt for correctness risks, memory lifetime issues, and performance bottlenecks.

File: ds4_metal.m

```c
"ds4_flash_attn_pad") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_kv_buffer,
                                         &g_flash_attn_kv_bytes,
                                         kv_f16_bytes,
                                         "ds4_flash_attn_kv_f16") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_tmp_buffer,
                                         &g_flash_attn_tmp_bytes,
                                         tmp_bytes,
                                         "ds4_flash_attn_tmp")) {
        return 0;
    }
    ds4_gpu_fill_raw_prefill_mask((uint16_t *)[mask_buffer contents], n_tokens, window);

    id<MTLComputePipelineState> pad_pipeline = nil;
    if ((n_tokens % ncpsg) != 0) {
        pad_pipeline = ds4_gpu_get_flash_attn_pad_pipeline(true, (int32_t)ncpsg);
        if (!pad_pipeline) return 0;
    }
    id<MTLComputePipelineState> vec_pipeline =
        ds4_gpu_get_flash_attn_vec_pipeline("kernel_flash_attn_ext_vec_f16_dk512_dv512",
                                              true, true, false, false, true,
                                              (int32_t)head_dim,
                                              (int32_t)head_dim,
                                              (int32_t)nsg,
                                              (int32_t)nwg);
    id<MTLComputePipelineState> reduce_pipeline =
        ds4_gpu_get_flash_attn_reduce_pipeline((int32_t)head_dim, (int32_t)nwg);
    if (!vec_pipeline || !reduce_pipeline) return 0;

    if (!ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                         rawbuf,
                                         ds4_gpu_tensor_offset(raw_kv),
                                         g_flash_attn_kv_buffer,
                                         kv_f16_offset,
                                         n_tokens * head_dim)) {
        return 0;
    }

    if ((n_tokens % ncpsg) != 0) {
        ds4_gpu_flash_attn_pad_args pad_args = {
            .ne11 = (int32_t)n_tokens,
            .ne_12_2 = 1,
            .ne_12_3 = 1,
            .nb11 = row_bytes_f16,
            .nb12 = (uint64_t)n_tokens * row_bytes_f16,
            .nb13 = (uint64_t)n_tokens * row_bytes_f16,
            .nb21 = row_bytes_f16,
            .nb22 = (uint64_t)n_tokens * row_bytes_f16,
            .nb23 = (uint64_t)n_tokens * row_bytes_f16,
            .ne31 = (int32_t)n_tokens,
            .ne32 = 1,
            .ne33 = 1,
            .nb31 = (uint64_t)n_tokens * sizeof(uint16_t),
            .nb32 = mask_bytes,
            .nb33 = mask_bytes,
        };
```<｜Assistant｜><think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Review this excerpt for correctness risks, memory lifetime issues, and performance bottlenecks.

File: ds4_metal.m

```c
fprintf(stderr, "ds4: Metal %s function not found: %s\n",
                function_name, [[error localizedDescription] UTF8String]);
        return nil;
    }

    error = nil;
    id<MTLComputePipelineState> pipeline = [g_device newComputePipelineStateWithFunction:fn error:&error];
    if (!pipeline) {
        fprintf(stderr, "ds4: Metal %s pipeline failed: %s\n",
                function_name, [[error localizedDescription] UTF8String]);
        return nil;
    }

    [g_pipeline_cache setObject:pipeline forKey:key];
    return pipeline;
}

static id<MTLComputePipelineState> ds4_gpu_get_flash_attn_reduce_pipeline(
        int32_t dv,
        int32_t nwg) {
    NSString *key = [NSString stringWithFormat:@"kernel_flash_attn_ext_vec_reduce_dv=%d_nwg=%d",
                     (int)dv, (int)nwg];
    id<MTLComputePipelineState> cached = [g_pipeline_cache objectForKey:key];
    if (cached) return cached;

    MTLFunctionConstantValues *constants = [[MTLFunctionConstantValues alloc] init];
    [constants setConstantValue:&dv  type:MTLDataTypeInt atIndex:500];
    [constants setConstantValue:&nwg type:MTLDataTypeInt atIndex:501];

    NSError *error = nil;
    id<MTLFunction> fn = [g_library newFunctionWithName:@"kernel_flash_attn_ext_vec_reduce"
                                         constantValues:constants
                                                  error:&error];
    if (!fn) {
        fprintf(stderr, "ds4: Metal kernel_flash_attn_ext_vec_reduce function not found: %s\n",
                [[error localizedDescription] UTF8String]);
        return nil;
    }

    error = nil;
    id<MTLComputePipelineState> pipeline = [g_device newComputePipelineStateWithFunction:fn error:&error];
    if (!pipeline) {
        fprintf(stderr, "ds4: Metal kernel_flash_attn_ext_vec_reduce pipeline failed: %s\n",
                [[error localizedDescription] UTF8String]);
        return nil;
    }

    [g_pipeline_cache setObject:pipeline forKey:key];
    return pipeline;
}

static uint32_t ds4_gpu_flash_attn_vec_nsg(uint32_t n_keys, uint32_t nwg, uint32_t ncpsg) {
    uint32_t nsg = 1;
    while (2u * nwg * nsg * ncpsg < n_keys && nsg < 4u) {
        nsg *= 2u;
    }
    return nsg;
}

static int ds4_gpu_trace_allocs(void) {
    static int initialized;
    static int enabled;
    if (!initialized) {
        enabled = getenv("DS4_METAL_TRACE_ALLOCS") != NULL;
        initialized = 1;
    }
    return enabled;
}

static double ds4_gpu_mib(uint64_t bytes) {
    return (double)bytes / (1024.0 * 1024.0);
}

static double ds4_gpu_gib(uint64_t bytes) {
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Review this excerpt for correctness risks, memory lifetime issues, and performance bottlenecks.

File: ds4_metal.m

```c
fprintf(stderr, "ds4: Metal %s function not found: %s\n",
                function_name, [[error localizedDescription] UTF8String]);
        return nil;
    }

    error = nil;
    id<MTLComputePipelineState> pipeline = [g_device newComputePipelineStateWithFunction:fn error:&error];
    if (!pipeline) {
        fprintf(stderr, "ds4: Metal %s pipeline failed: %s\n",
                function_name, [[error localizedDescription] UTF8String]);
        return nil;
    }

    [g_pipeline_cache setObject:pipeline forKey:key];
    return pipeline;
}

static id<MTLComputePipelineState> ds4_gpu_get_flash_attn_reduce_pipeline(
        int32_t dv,
        int32_t nwg) {
    NSString *key = [NSString stringWithFormat:@"kernel_flash_attn_ext_vec_reduce_dv=%d_nwg=%d",
                     (int)dv, (int)nwg];
    id<MTLComputePipelineState> cached = [g_pipeline_cache objectForKey:key];
    if (cached) return cached;

    MTLFunctionConstantValues *constants = [[MTLFunctionConstantValues alloc] init];
    [constants setConstantValue:&dv  type:MTLDataTypeInt atIndex:500];
    [constants setConstantValue:&nwg type:MTLDataTypeInt atIndex:501];

    NSError *error = nil;
    id<MTLFunction> fn = [g_library newFunctionWithName:@"kernel_flash_attn_ext_vec_reduce"
                                         constantValues:constants
                                                  error:&error];
    if (!fn) {
        fprintf(stderr, "ds4: Metal kernel_flash_attn_ext_vec_reduce function not found: %s\n",
                [[error localizedDescription] UTF8String]);
        return nil;
    }

    error = nil;
    id<MTLComputePipelineState> pipeline = [g_device newComputePipelineStateWithFunction:fn error:&error];
    if (!pipeline) {
        fprintf(stderr, "ds4: Metal kernel_flash_attn_ext_vec_reduce pipeline failed: %s\n",
                [[error localizedDescription] UTF8String]);
        return nil;
    }

    [g_pipeline_cache setObject:pipeline forKey:key];
    return pipeline;
}

static uint32_t ds4_gpu_flash_attn_vec_nsg(uint32_t n_keys, uint32_t nwg, uint32_t ncpsg) {
    uint32_t nsg = 1;
    while (2u * nwg * nsg * ncpsg < n_keys && nsg < 4u) {
        nsg *= 2u;
    }
    return nsg;
}

static int ds4_gpu_trace_allocs(void) {
    static int initialized;
    static int enabled;
    if (!initialized) {
        enabled = getenv("DS4_METAL_TRACE_ALLOCS") != NULL;
        initialized = 1;
    }
    return enabled;
}

static double ds4_gpu_mib(uint64_t bytes) {
    return (double)bytes / (1024.0 * 1024.0);
}

static double ds4_gpu_gib(uint64_t bytes) {
```<｜Assistant｜></think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Review this excerpt for correctness risks, memory lifetime issues, and performance bottlenecks.

File: ds4_metal.m

```c
fprintf(stderr, "ds4: Metal %s function not found: %s\n",
                function_name, [[error localizedDescription] UTF8String]);
        return nil;
    }

    error = nil;
    id<MTLComputePipelineState> pipeline = [g_device newComputePipelineStateWithFunction:fn error:&error];
    if (!pipeline) {
        fprintf(stderr, "ds4: Metal %s pipeline failed: %s\n",
                function_name, [[error localizedDescription] UTF8String]);
        return nil;
    }

    [g_pipeline_cache setObject:pipeline forKey:key];
    return pipeline;
}

static id<MTLComputePipelineState> ds4_gpu_get_flash_attn_reduce_pipeline(
        int32_t dv,
        int32_t nwg) {
    NSString *key = [NSString stringWithFormat:@"kernel_flash_attn_ext_vec_reduce_dv=%d_nwg=%d",
                     (int)dv, (int)nwg];
    id<MTLComputePipelineState> cached = [g_pipeline_cache objectForKey:key];
    if (cached) return cached;

    MTLFunctionConstantValues *constants = [[MTLFunctionConstantValues alloc] init];
    [constants setConstantValue:&dv  type:MTLDataTypeInt atIndex:500];
    [constants setConstantValue:&nwg type:MTLDataTypeInt atIndex:501];

    NSError *error = nil;
    id<MTLFunction> fn = [g_library newFunctionWithName:@"kernel_flash_attn_ext_vec_reduce"
                                         constantValues:constants
                                                  error:&error];
    if (!fn) {
        fprintf(stderr, "ds4: Metal kernel_flash_attn_ext_vec_reduce function not found: %s\n",
                [[error localizedDescription] UTF8String]);
        return nil;
    }

    error = nil;
    id<MTLComputePipelineState> pipeline = [g_device newComputePipelineStateWithFunction:fn error:&error];
    if (!pipeline) {
        fprintf(stderr, "ds4: Metal kernel_flash_attn_ext_vec_reduce pipeline failed: %s\n",
                [[error localizedDescription] UTF8String]);
        return nil;
    }

    [g_pipeline_cache setObject:pipeline forKey:key];
    return pipeline;
}

static uint32_t ds4_gpu_flash_attn_vec_nsg(uint32_t n_keys, uint32_t nwg, uint32_t ncpsg) {
    uint32_t nsg = 1;
    while (2u * nwg * nsg * ncpsg < n_keys && nsg < 4u) {
        nsg *= 2u;
    }
    return nsg;
}

static int ds4_gpu_trace_allocs(void) {
    static int initialized;
    static int enabled;
    if (!initialized) {
        enabled = getenv("DS4_METAL_TRACE_ALLOCS") != NULL;
        initialized = 1;
    }
    return enabled;
}

static double ds4_gpu_mib(uint64_t bytes) {
    return (double)bytes / (1024.0 * 1024.0);
}

static double ds4_gpu_gib(uint64_t bytes) {
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Review this excerpt for correctness risks, memory lifetime issues, and performance bottlenecks.

File: ds4_metal.m

```c
fprintf(stderr, "ds4: Metal %s function not found: %s\n",
                function_name, [[error localizedDescription] UTF8String]);
        return nil;
    }

    error = nil;
    id<MTLComputePipelineState> pipeline = [g_device newComputePipelineStateWithFunction:fn error:&error];
    if (!pipeline) {
        fprintf(stderr, "ds4: Metal %s pipeline failed: %s\n",
                function_name, [[error localizedDescription] UTF8String]);
        return nil;
    }

    [g_pipeline_cache setObject:pipeline forKey:key];
    return pipeline;
}

static id<MTLComputePipelineState> ds4_gpu_get_flash_attn_reduce_pipeline(
        int32_t dv,
        int32_t nwg) {
    NSString *key = [NSString stringWithFormat:@"kernel_flash_attn_ext_vec_reduce_dv=%d_nwg=%d",
                     (int)dv, (int)nwg];
    id<MTLComputePipelineState> cached = [g_pipeline_cache objectForKey:key];
    if (cached) return cached;

    MTLFunctionConstantValues *constants = [[MTLFunctionConstantValues alloc] init];
    [constants setConstantValue:&dv  type:MTLDataTypeInt atIndex:500];
    [constants setConstantValue:&nwg type:MTLDataTypeInt atIndex:501];

    NSError *error = nil;
    id<MTLFunction> fn = [g_library newFunctionWithName:@"kernel_flash_attn_ext_vec_reduce"
                                         constantValues:constants
                                                  error:&error];
    if (!fn) {
        fprintf(stderr, "ds4: Metal kernel_flash_attn_ext_vec_reduce function not found: %s\n",
                [[error localizedDescription] UTF8String]);
        return nil;
    }

    error = nil;
    id<MTLComputePipelineState> pipeline = [g_device newComputePipelineStateWithFunction:fn error:&error];
    if (!pipeline) {
        fprintf(stderr, "ds4: Metal kernel_flash_attn_ext_vec_reduce pipeline failed: %s\n",
                [[error localizedDescription] UTF8String]);
        return nil;
    }

    [g_pipeline_cache setObject:pipeline forKey:key];
    return pipeline;
}

static uint32_t ds4_gpu_flash_attn_vec_nsg(uint32_t n_keys, uint32_t nwg, uint32_t ncpsg) {
    uint32_t nsg = 1;
    while (2u * nwg * nsg * ncpsg < n_keys && nsg < 4u) {
        nsg *= 2u;
    }
    return nsg;
}

static int ds4_gpu_trace_allocs(void) {
    static int initialized;
    static int enabled;
    if (!initialized) {
        enabled = getenv("DS4_METAL_TRACE_ALLOCS") != NULL;
        initialized = 1;
    }
    return enabled;
}

static double ds4_gpu_mib(uint64_t bytes) {
    return (double)bytes / (1024.0 * 1024.0);
}

static double ds4_gpu_gib(uint64_t bytes) {
```<｜Assistant｜><think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Explain what this code does and identify the inference stage it belongs to.

File: ds4_metal.m

```c
.ne32 = 1,
            .ne33 = 1,
            .nb31 = (uint64_t)n_tokens * sizeof(uint16_t),
            .nb32 = mask_bytes,
            .nb33 = mask_bytes,
        };

        id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
        [enc setComputePipelineState:pad_pipeline];
        [enc setBytes:&pad_args length:sizeof(pad_args) atIndex:0];
        [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:1];
        [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:2];
        [enc setBuffer:mask_buffer offset:0 atIndex:3];
        [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:4];
        [enc dispatchThreadgroups:MTLSizeMake(ncpsg, 1, 1)
             threadsPerThreadgroup:MTLSizeMake(32, 1, 1)];
        ds4_gpu_end_compute_encoder(cb, enc);
    }

    ds4_gpu_flash_attn_vec_args vec_args = {
        .ne01 = (int32_t)n_tokens,
        .ne02 = (int32_t)n_head,
        .ne03 = 1,
        .nb01 = (uint64_t)n_head * row_bytes,
        .nb02 = row_bytes,
        .nb03 = (uint64_t)n_tokens * n_head * row_bytes,
        .ne11 = (int32_t)n_tokens,
        .ne_12_2 = 1,
        .ne_12_3 = 1,
        .ns10 = (int32_t)head_dim,
        .nb11 = row_bytes_f16,
        .nb12 = (uint64_t)n_tokens * row_bytes_f16,
        .nb13 = (uint64_t)n_tokens * row_bytes_f16,
        .ns20 = (int32_t)head_dim,
        .nb21 = row_bytes_f16,
        .nb22 = (uint64_t)n_tokens * row_bytes_f16,
        .nb23 = (uint64_t)n_tokens * row_bytes_f16,
        .ne31 = (int32_t)n_tokens,
        .ne32 = 1,
        .ne33 = 1,
        .nb31 = (uint64_t)n_tokens * sizeof(uint16_t),
        .nb32 = mask_bytes,
        .nb33 = mask_bytes,
        .ne1 = (int32_t)n_head,
        .ne2 = (int32_t)n_tokens,
        .ne3 = 1,
        .scale = 1.0f / sqrtf((float)head_dim),
        .max_bias = 0.0f,
        .m0 = 0.0f,
        .m1 = 0.0f,
        .n_head_log2 = 0,
        .logit_softcap = 0.0f,
    };

    const NSUInteger shared_elems = (ds4_gpu_align_up_ns(head_dim, 128u) +
                                     4u * ncpsg +
                                     2u * ds4_gpu_align_up_ns(head_dim, 128u)) * nsg;
    const NSUInteger shared_bytes = ds4_gpu_align_up_ns(shared_elems * (sizeof(float) / 2u), 16u);

    id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
    [enc setComputePipelineState:vec_pipeline];
    [enc setBytes:&vec_args length:sizeof(vec_args) atIndex:0];
    [enc setBuffer:qbuf offset:ds4_gpu_tensor_offset(q) atIndex:1];
    [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:2];
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Explain what this code does and identify the inference stage it belongs to.

File: ds4_metal.m

```c
.ne32 = 1,
            .ne33 = 1,
            .nb31 = (uint64_t)n_tokens * sizeof(uint16_t),
            .nb32 = mask_bytes,
            .nb33 = mask_bytes,
        };

        id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
        [enc setComputePipelineState:pad_pipeline];
        [enc setBytes:&pad_args length:sizeof(pad_args) atIndex:0];
        [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:1];
        [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:2];
        [enc setBuffer:mask_buffer offset:0 atIndex:3];
        [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:4];
        [enc dispatchThreadgroups:MTLSizeMake(ncpsg, 1, 1)
             threadsPerThreadgroup:MTLSizeMake(32, 1, 1)];
        ds4_gpu_end_compute_encoder(cb, enc);
    }

    ds4_gpu_flash_attn_vec_args vec_args = {
        .ne01 = (int32_t)n_tokens,
        .ne02 = (int32_t)n_head,
        .ne03 = 1,
        .nb01 = (uint64_t)n_head * row_bytes,
        .nb02 = row_bytes,
        .nb03 = (uint64_t)n_tokens * n_head * row_bytes,
        .ne11 = (int32_t)n_tokens,
        .ne_12_2 = 1,
        .ne_12_3 = 1,
        .ns10 = (int32_t)head_dim,
        .nb11 = row_bytes_f16,
        .nb12 = (uint64_t)n_tokens * row_bytes_f16,
        .nb13 = (uint64_t)n_tokens * row_bytes_f16,
        .ns20 = (int32_t)head_dim,
        .nb21 = row_bytes_f16,
        .nb22 = (uint64_t)n_tokens * row_bytes_f16,
        .nb23 = (uint64_t)n_tokens * row_bytes_f16,
        .ne31 = (int32_t)n_tokens,
        .ne32 = 1,
        .ne33 = 1,
        .nb31 = (uint64_t)n_tokens * sizeof(uint16_t),
        .nb32 = mask_bytes,
        .nb33 = mask_bytes,
        .ne1 = (int32_t)n_head,
        .ne2 = (int32_t)n_tokens,
        .ne3 = 1,
        .scale = 1.0f / sqrtf((float)head_dim),
        .max_bias = 0.0f,
        .m0 = 0.0f,
        .m1 = 0.0f,
        .n_head_log2 = 0,
        .logit_softcap = 0.0f,
    };

    const NSUInteger shared_elems = (ds4_gpu_align_up_ns(head_dim, 128u) +
                                     4u * ncpsg +
                                     2u * ds4_gpu_align_up_ns(head_dim, 128u)) * nsg;
    const NSUInteger shared_bytes = ds4_gpu_align_up_ns(shared_elems * (sizeof(float) / 2u), 16u);

    id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
    [enc setComputePipelineState:vec_pipeline];
    [enc setBytes:&vec_args length:sizeof(vec_args) atIndex:0];
    [enc setBuffer:qbuf offset:ds4_gpu_tensor_offset(q) atIndex:1];
    [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:2];
```<｜Assistant｜></think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Explain what this code does and identify the inference stage it belongs to.

File: ds4_metal.m

```c
.ne32 = 1,
            .ne33 = 1,
            .nb31 = (uint64_t)n_tokens * sizeof(uint16_t),
            .nb32 = mask_bytes,
            .nb33 = mask_bytes,
        };

        id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
        [enc setComputePipelineState:pad_pipeline];
        [enc setBytes:&pad_args length:sizeof(pad_args) atIndex:0];
        [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:1];
        [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:2];
        [enc setBuffer:mask_buffer offset:0 atIndex:3];
        [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:4];
        [enc dispatchThreadgroups:MTLSizeMake(ncpsg, 1, 1)
             threadsPerThreadgroup:MTLSizeMake(32, 1, 1)];
        ds4_gpu_end_compute_encoder(cb, enc);
    }

    ds4_gpu_flash_attn_vec_args vec_args = {
        .ne01 = (int32_t)n_tokens,
        .ne02 = (int32_t)n_head,
        .ne03 = 1,
        .nb01 = (uint64_t)n_head * row_bytes,
        .nb02 = row_bytes,
        .nb03 = (uint64_t)n_tokens * n_head * row_bytes,
        .ne11 = (int32_t)n_tokens,
        .ne_12_2 = 1,
        .ne_12_3 = 1,
        .ns10 = (int32_t)head_dim,
        .nb11 = row_bytes_f16,
        .nb12 = (uint64_t)n_tokens * row_bytes_f16,
        .nb13 = (uint64_t)n_tokens * row_bytes_f16,
        .ns20 = (int32_t)head_dim,
        .nb21 = row_bytes_f16,
        .nb22 = (uint64_t)n_tokens * row_bytes_f16,
        .nb23 = (uint64_t)n_tokens * row_bytes_f16,
        .ne31 = (int32_t)n_tokens,
        .ne32 = 1,
        .ne33 = 1,
        .nb31 = (uint64_t)n_tokens * sizeof(uint16_t),
        .nb32 = mask_bytes,
        .nb33 = mask_bytes,
        .ne1 = (int32_t)n_head,
        .ne2 = (int32_t)n_tokens,
        .ne3 = 1,
        .scale = 1.0f / sqrtf((float)head_dim),
        .max_bias = 0.0f,
        .m0 = 0.0f,
        .m1 = 0.0f,
        .n_head_log2 = 0,
        .logit_softcap = 0.0f,
    };

    const NSUInteger shared_elems = (ds4_gpu_align_up_ns(head_dim, 128u) +
                                     4u * ncpsg +
                                     2u * ds4_gpu_align_up_ns(head_dim, 128u)) * nsg;
    const NSUInteger shared_bytes = ds4_gpu_align_up_ns(shared_elems * (sizeof(float) / 2u), 16u);

    id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
    [enc setComputePipelineState:vec_pipeline];
    [enc setBytes:&vec_args length:sizeof(vec_args) atIndex:0];
    [enc setBuffer:qbuf offset:ds4_gpu_tensor_offset(q) atIndex:1];
    [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:2];
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Explain what this code does and identify the inference stage it belongs to.

File: ds4_metal.m

```c
.ne32 = 1,
            .ne33 = 1,
            .nb31 = (uint64_t)n_tokens * sizeof(uint16_t),
            .nb32 = mask_bytes,
            .nb33 = mask_bytes,
        };

        id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
        [enc setComputePipelineState:pad_pipeline];
        [enc setBytes:&pad_args length:sizeof(pad_args) atIndex:0];
        [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:1];
        [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:2];
        [enc setBuffer:mask_buffer offset:0 atIndex:3];
        [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:4];
        [enc dispatchThreadgroups:MTLSizeMake(ncpsg, 1, 1)
             threadsPerThreadgroup:MTLSizeMake(32, 1, 1)];
        ds4_gpu_end_compute_encoder(cb, enc);
    }

    ds4_gpu_flash_attn_vec_args vec_args = {
        .ne01 = (int32_t)n_tokens,
        .ne02 = (int32_t)n_head,
        .ne03 = 1,
        .nb01 = (uint64_t)n_head * row_bytes,
        .nb02 = row_bytes,
        .nb03 = (uint64_t)n_tokens * n_head * row_bytes,
        .ne11 = (int32_t)n_tokens,
        .ne_12_2 = 1,
        .ne_12_3 = 1,
        .ns10 = (int32_t)head_dim,
        .nb11 = row_bytes_f16,
        .nb12 = (uint64_t)n_tokens * row_bytes_f16,
        .nb13 = (uint64_t)n_tokens * row_bytes_f16,
        .ns20 = (int32_t)head_dim,
        .nb21 = row_bytes_f16,
        .nb22 = (uint64_t)n_tokens * row_bytes_f16,
        .nb23 = (uint64_t)n_tokens * row_bytes_f16,
        .ne31 = (int32_t)n_tokens,
        .ne32 = 1,
        .ne33 = 1,
        .nb31 = (uint64_t)n_tokens * sizeof(uint16_t),
        .nb32 = mask_bytes,
        .nb33 = mask_bytes,
        .ne1 = (int32_t)n_head,
        .ne2 = (int32_t)n_tokens,
        .ne3 = 1,
        .scale = 1.0f / sqrtf((float)head_dim),
        .max_bias = 0.0f,
        .m0 = 0.0f,
        .m1 = 0.0f,
        .n_head_log2 = 0,
        .logit_softcap = 0.0f,
    };

    const NSUInteger shared_elems = (ds4_gpu_align_up_ns(head_dim, 128u) +
                                     4u * ncpsg +
                                     2u * ds4_gpu_align_up_ns(head_dim, 128u)) * nsg;
    const NSUInteger shared_bytes = ds4_gpu_align_up_ns(shared_elems * (sizeof(float) / 2u), 16u);

    id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
    [enc setComputePipelineState:vec_pipeline];
    [enc setBytes:&vec_args length:sizeof(vec_args) atIndex:0];
    [enc setBuffer:qbuf offset:ds4_gpu_tensor_offset(q) atIndex:1];
    [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:2];
```<｜Assistant｜><think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Suggest a minimal correctness-preserving optimization for this excerpt.

File: ds4_metal.m

```c
s length:sizeof(vec_args) atIndex:0];
    [enc setBuffer:qbuf offset:ds4_gpu_tensor_offset(q) atIndex:1];
    [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:2];
    [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:3];
    [enc setBuffer:mask_buffer offset:0 atIndex:4];
    [enc setBuffer:sinks_buf offset:sinks_offset atIndex:5];
    [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:6];
    [enc setBuffer:g_flash_attn_tmp_buffer offset:0 atIndex:7];
    [enc setThreadgroupMemoryLength:shared_bytes atIndex:0];
    [enc dispatchThreadgroups:MTLSizeMake(n_tokens, n_head, nwg)
         threadsPerThreadgroup:MTLSizeMake(32, nsg, 1)];
    ds4_gpu_end_compute_encoder(cb, enc);

    ds4_gpu_flash_attn_reduce_args reduce_args = {
        .nrows = (int32_t)nrows,
    };
    enc = ds4_gpu_compute_encoder(cb);
    [enc setComputePipelineState:reduce_pipeline];
    [enc setBytes:&reduce_args length:sizeof(reduce_args) atIndex:0];
    [enc setBuffer:g_flash_attn_tmp_buffer offset:0 atIndex:1];
    [enc setBuffer:headsbuf offset:ds4_gpu_tensor_offset(heads) atIndex:2];
    [enc dispatchThreadgroups:MTLSizeMake(nrows, 1, 1)
         threadsPerThreadgroup:MTLSizeMake(32u * nwg, 1, 1)];
    ds4_gpu_end_compute_encoder(cb, enc);

    return 1;
}

static int ds4_gpu_encode_flash_attention_gathered_heads(
        id<MTLCommandBuffer>   cb,
        ds4_gpu_tensor      *heads,
        id<MTLBuffer>          sinks_buf,
        NSUInteger             sinks_offset,
        const ds4_gpu_tensor *q,
        const ds4_gpu_tensor *raw_kv,
        uint32_t               n_raw,
        uint32_t               raw_cap,
        uint32_t               raw_start,
        const ds4_gpu_tensor *comp_kv,
        uint32_t               n_comp,
        const ds4_gpu_tensor *comp_mask,
        uint32_t               use_mask,
        uint32_t               n_head,
        uint32_t               head_dim) {
    const uint32_t n_keys = n_raw + n_comp;
    if (head_dim != 512 || n_head == 0 || n_raw == 0 || n_keys == 0 ||
        raw_cap < n_raw || n_keys < n_raw) {
        return 0;
    }

    id<MTLBuffer> qbuf = ds4_gpu_tensor_buffer(q);
    id<MTLBuffer> rawbuf = ds4_gpu_tensor_buffer(raw_kv);
    id<MTLBuffer> compbuf = n_comp ? ds4_gpu_tensor_buffer(comp_kv) : nil;
    id<MTLBuffer> headsbuf = ds4_gpu_tensor_buffer(heads);
    id<MTLBuffer> maskbuf = use_mask ? ds4_gpu_tensor_buffer(comp_mask) : nil;
    const uint64_t q_bytes = (uint64_t)n_head * head_dim * sizeof(float);
    const uint64_t raw_bytes = (uint64_t)raw_cap * head_dim * sizeof(float);
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Suggest a minimal correctness-preserving optimization for this excerpt.

File: ds4_metal.m

```c
s length:sizeof(vec_args) atIndex:0];
    [enc setBuffer:qbuf offset:ds4_gpu_tensor_offset(q) atIndex:1];
    [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:2];
    [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:3];
    [enc setBuffer:mask_buffer offset:0 atIndex:4];
    [enc setBuffer:sinks_buf offset:sinks_offset atIndex:5];
    [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:6];
    [enc setBuffer:g_flash_attn_tmp_buffer offset:0 atIndex:7];
    [enc setThreadgroupMemoryLength:shared_bytes atIndex:0];
    [enc dispatchThreadgroups:MTLSizeMake(n_tokens, n_head, nwg)
         threadsPerThreadgroup:MTLSizeMake(32, nsg, 1)];
    ds4_gpu_end_compute_encoder(cb, enc);

    ds4_gpu_flash_attn_reduce_args reduce_args = {
        .nrows = (int32_t)nrows,
    };
    enc = ds4_gpu_compute_encoder(cb);
    [enc setComputePipelineState:reduce_pipeline];
    [enc setBytes:&reduce_args length:sizeof(reduce_args) atIndex:0];
    [enc setBuffer:g_flash_attn_tmp_buffer offset:0 atIndex:1];
    [enc setBuffer:headsbuf offset:ds4_gpu_tensor_offset(heads) atIndex:2];
    [enc dispatchThreadgroups:MTLSizeMake(nrows, 1, 1)
         threadsPerThreadgroup:MTLSizeMake(32u * nwg, 1, 1)];
    ds4_gpu_end_compute_encoder(cb, enc);

    return 1;
}

static int ds4_gpu_encode_flash_attention_gathered_heads(
        id<MTLCommandBuffer>   cb,
        ds4_gpu_tensor      *heads,
        id<MTLBuffer>          sinks_buf,
        NSUInteger             sinks_offset,
        const ds4_gpu_tensor *q,
        const ds4_gpu_tensor *raw_kv,
        uint32_t               n_raw,
        uint32_t               raw_cap,
        uint32_t               raw_start,
        const ds4_gpu_tensor *comp_kv,
        uint32_t               n_comp,
        const ds4_gpu_tensor *comp_mask,
        uint32_t               use_mask,
        uint32_t               n_head,
        uint32_t               head_dim) {
    const uint32_t n_keys = n_raw + n_comp;
    if (head_dim != 512 || n_head == 0 || n_raw == 0 || n_keys == 0 ||
        raw_cap < n_raw || n_keys < n_raw) {
        return 0;
    }

    id<MTLBuffer> qbuf = ds4_gpu_tensor_buffer(q);
    id<MTLBuffer> rawbuf = ds4_gpu_tensor_buffer(raw_kv);
    id<MTLBuffer> compbuf = n_comp ? ds4_gpu_tensor_buffer(comp_kv) : nil;
    id<MTLBuffer> headsbuf = ds4_gpu_tensor_buffer(heads);
    id<MTLBuffer> maskbuf = use_mask ? ds4_gpu_tensor_buffer(comp_mask) : nil;
    const uint64_t q_bytes = (uint64_t)n_head * head_dim * sizeof(float);
    const uint64_t raw_bytes = (uint64_t)raw_cap * head_dim * sizeof(float);
```<｜Assistant｜></think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Suggest a minimal correctness-preserving optimization for this excerpt.

File: ds4_metal.m

```c
s length:sizeof(vec_args) atIndex:0];
    [enc setBuffer:qbuf offset:ds4_gpu_tensor_offset(q) atIndex:1];
    [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:2];
    [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:3];
    [enc setBuffer:mask_buffer offset:0 atIndex:4];
    [enc setBuffer:sinks_buf offset:sinks_offset atIndex:5];
    [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:6];
    [enc setBuffer:g_flash_attn_tmp_buffer offset:0 atIndex:7];
    [enc setThreadgroupMemoryLength:shared_bytes atIndex:0];
    [enc dispatchThreadgroups:MTLSizeMake(n_tokens, n_head, nwg)
         threadsPerThreadgroup:MTLSizeMake(32, nsg, 1)];
    ds4_gpu_end_compute_encoder(cb, enc);

    ds4_gpu_flash_attn_reduce_args reduce_args = {
        .nrows = (int32_t)nrows,
    };
    enc = ds4_gpu_compute_encoder(cb);
    [enc setComputePipelineState:reduce_pipeline];
    [enc setBytes:&reduce_args length:sizeof(reduce_args) atIndex:0];
    [enc setBuffer:g_flash_attn_tmp_buffer offset:0 atIndex:1];
    [enc setBuffer:headsbuf offset:ds4_gpu_tensor_offset(heads) atIndex:2];
    [enc dispatchThreadgroups:MTLSizeMake(nrows, 1, 1)
         threadsPerThreadgroup:MTLSizeMake(32u * nwg, 1, 1)];
    ds4_gpu_end_compute_encoder(cb, enc);

    return 1;
}

static int ds4_gpu_encode_flash_attention_gathered_heads(
        id<MTLCommandBuffer>   cb,
        ds4_gpu_tensor      *heads,
        id<MTLBuffer>          sinks_buf,
        NSUInteger             sinks_offset,
        const ds4_gpu_tensor *q,
        const ds4_gpu_tensor *raw_kv,
        uint32_t               n_raw,
        uint32_t               raw_cap,
        uint32_t               raw_start,
        const ds4_gpu_tensor *comp_kv,
        uint32_t               n_comp,
        const ds4_gpu_tensor *comp_mask,
        uint32_t               use_mask,
        uint32_t               n_head,
        uint32_t               head_dim) {
    const uint32_t n_keys = n_raw + n_comp;
    if (head_dim != 512 || n_head == 0 || n_raw == 0 || n_keys == 0 ||
        raw_cap < n_raw || n_keys < n_raw) {
        return 0;
    }

    id<MTLBuffer> qbuf = ds4_gpu_tensor_buffer(q);
    id<MTLBuffer> rawbuf = ds4_gpu_tensor_buffer(raw_kv);
    id<MTLBuffer> compbuf = n_comp ? ds4_gpu_tensor_buffer(comp_kv) : nil;
    id<MTLBuffer> headsbuf = ds4_gpu_tensor_buffer(heads);
    id<MTLBuffer> maskbuf = use_mask ? ds4_gpu_tensor_buffer(comp_mask) : nil;
    const uint64_t q_bytes = (uint64_t)n_head * head_dim * sizeof(float);
    const uint64_t raw_bytes = (uint64_t)raw_cap * head_dim * sizeof(float);
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Suggest a minimal correctness-preserving optimization for this excerpt.

File: ds4_metal.m

```c
s length:sizeof(vec_args) atIndex:0];
    [enc setBuffer:qbuf offset:ds4_gpu_tensor_offset(q) atIndex:1];
    [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:2];
    [enc setBuffer:g_flash_attn_kv_buffer offset:kv_f16_offset atIndex:3];
    [enc setBuffer:mask_buffer offset:0 atIndex:4];
    [enc setBuffer:sinks_buf offset:sinks_offset atIndex:5];
    [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:6];
    [enc setBuffer:g_flash_attn_tmp_buffer offset:0 atIndex:7];
    [enc setThreadgroupMemoryLength:shared_bytes atIndex:0];
    [enc dispatchThreadgroups:MTLSizeMake(n_tokens, n_head, nwg)
         threadsPerThreadgroup:MTLSizeMake(32, nsg, 1)];
    ds4_gpu_end_compute_encoder(cb, enc);

    ds4_gpu_flash_attn_reduce_args reduce_args = {
        .nrows = (int32_t)nrows,
    };
    enc = ds4_gpu_compute_encoder(cb);
    [enc setComputePipelineState:reduce_pipeline];
    [enc setBytes:&reduce_args length:sizeof(reduce_args) atIndex:0];
    [enc setBuffer:g_flash_attn_tmp_buffer offset:0 atIndex:1];
    [enc setBuffer:headsbuf offset:ds4_gpu_tensor_offset(heads) atIndex:2];
    [enc dispatchThreadgroups:MTLSizeMake(nrows, 1, 1)
         threadsPerThreadgroup:MTLSizeMake(32u * nwg, 1, 1)];
    ds4_gpu_end_compute_encoder(cb, enc);

    return 1;
}

static int ds4_gpu_encode_flash_attention_gathered_heads(
        id<MTLCommandBuffer>   cb,
        ds4_gpu_tensor      *heads,
        id<MTLBuffer>          sinks_buf,
        NSUInteger             sinks_offset,
        const ds4_gpu_tensor *q,
        const ds4_gpu_tensor *raw_kv,
        uint32_t               n_raw,
        uint32_t               raw_cap,
        uint32_t               raw_start,
        const ds4_gpu_tensor *comp_kv,
        uint32_t               n_comp,
        const ds4_gpu_tensor *comp_mask,
        uint32_t               use_mask,
        uint32_t               n_head,
        uint32_t               head_dim) {
    const uint32_t n_keys = n_raw + n_comp;
    if (head_dim != 512 || n_head == 0 || n_raw == 0 || n_keys == 0 ||
        raw_cap < n_raw || n_keys < n_raw) {
        return 0;
    }

    id<MTLBuffer> qbuf = ds4_gpu_tensor_buffer(q);
    id<MTLBuffer> rawbuf = ds4_gpu_tensor_buffer(raw_kv);
    id<MTLBuffer> compbuf = n_comp ? ds4_gpu_tensor_buffer(comp_kv) : nil;
    id<MTLBuffer> headsbuf = ds4_gpu_tensor_buffer(heads);
    id<MTLBuffer> maskbuf = use_mask ? ds4_gpu_tensor_buffer(comp_mask) : nil;
    const uint64_t q_bytes = (uint64_t)n_head * head_dim * sizeof(float);
    const uint64_t raw_bytes = (uint64_t)raw_cap * head_dim * sizeof(float);
```<｜Assistant｜><think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Trova bug sottili e spiega quali invarianti dell'inferenza possono rompersi.

File: ds4_metal.m

```c
nsor_buffer(comp_mask) : nil;
    const uint64_t q_bytes = (uint64_t)n_head * head_dim * sizeof(float);
    const uint64_t raw_bytes = (uint64_t)raw_cap * head_dim * sizeof(float);
    const uint64_t comp_bytes = (uint64_t)n_comp * head_dim * sizeof(float);
    const uint64_t comp_mask_bytes = use_mask ? (uint64_t)n_comp * sizeof(float) : 0u;
    if (!qbuf || !rawbuf || !headsbuf || !sinks_buf ||
        (n_comp && !compbuf) ||
        (use_mask && !maskbuf) ||
        ds4_gpu_tensor_bytes(q) < q_bytes ||
        ds4_gpu_tensor_bytes(raw_kv) < raw_bytes ||
        (n_comp && ds4_gpu_tensor_bytes(comp_kv) < comp_bytes) ||
        ds4_gpu_tensor_bytes(heads) < q_bytes ||
        (use_mask && ds4_gpu_tensor_bytes(comp_mask) < comp_mask_bytes)) {
        fprintf(stderr, "ds4: Metal gathered DS4 FlashAttention received undersized buffers\n");
        return 0;
    }

    const uint32_t ncpsg = 32;
    const uint32_t nwg = 32;
    const uint32_t nsg = ds4_gpu_flash_attn_vec_nsg(n_keys, nwg, ncpsg);
    const NSUInteger row_bytes = (NSUInteger)head_dim * sizeof(float);
    const NSUInteger row_bytes_f16 = (NSUInteger)head_dim * sizeof(uint16_t);
    const NSUInteger mask_bytes = (NSUInteger)n_keys * sizeof(uint16_t);
    const NSUInteger kv_bytes = (NSUInteger)n_keys * row_bytes_f16;
    const NSUInteger pad_bytes = 2u * (NSUInteger)ncpsg * row_bytes_f16 +
                                 (NSUInteger)ncpsg * sizeof(uint16_t);
    const NSUInteger nrows = (NSUInteger)n_head;
    const NSUInteger tmp_bytes = nrows * (NSUInteger)head_dim * (NSUInteger)nwg * sizeof(float) +
                                 nrows * (2u * (NSUInteger)nwg) * sizeof(float);

    if (!ds4_gpu_ensure_scratch_buffer(&g_flash_attn_mask_buffer,
                                         &g_flash_attn_mask_bytes,
                                         mask_bytes,
                                         "ds4_flash_attn_mask") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_kv_buffer,
                                         &g_flash_attn_kv_bytes,
                                         kv_bytes,
                                         "ds4_flash_attn_kv") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_pad_buffer,
                                         &g_flash_attn_pad_bytes,
                                         pad_bytes,
                                         "ds4_flash_attn_pad") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_tmp_buffer,
                                         &g_flash_attn_tmp_bytes,
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Trova bug sottili e spiega quali invarianti dell'inferenza possono rompersi.

File: ds4_metal.m

```c
nsor_buffer(comp_mask) : nil;
    const uint64_t q_bytes = (uint64_t)n_head * head_dim * sizeof(float);
    const uint64_t raw_bytes = (uint64_t)raw_cap * head_dim * sizeof(float);
    const uint64_t comp_bytes = (uint64_t)n_comp * head_dim * sizeof(float);
    const uint64_t comp_mask_bytes = use_mask ? (uint64_t)n_comp * sizeof(float) : 0u;
    if (!qbuf || !rawbuf || !headsbuf || !sinks_buf ||
        (n_comp && !compbuf) ||
        (use_mask && !maskbuf) ||
        ds4_gpu_tensor_bytes(q) < q_bytes ||
        ds4_gpu_tensor_bytes(raw_kv) < raw_bytes ||
        (n_comp && ds4_gpu_tensor_bytes(comp_kv) < comp_bytes) ||
        ds4_gpu_tensor_bytes(heads) < q_bytes ||
        (use_mask && ds4_gpu_tensor_bytes(comp_mask) < comp_mask_bytes)) {
        fprintf(stderr, "ds4: Metal gathered DS4 FlashAttention received undersized buffers\n");
        return 0;
    }

    const uint32_t ncpsg = 32;
    const uint32_t nwg = 32;
    const uint32_t nsg = ds4_gpu_flash_attn_vec_nsg(n_keys, nwg, ncpsg);
    const NSUInteger row_bytes = (NSUInteger)head_dim * sizeof(float);
    const NSUInteger row_bytes_f16 = (NSUInteger)head_dim * sizeof(uint16_t);
    const NSUInteger mask_bytes = (NSUInteger)n_keys * sizeof(uint16_t);
    const NSUInteger kv_bytes = (NSUInteger)n_keys * row_bytes_f16;
    const NSUInteger pad_bytes = 2u * (NSUInteger)ncpsg * row_bytes_f16 +
                                 (NSUInteger)ncpsg * sizeof(uint16_t);
    const NSUInteger nrows = (NSUInteger)n_head;
    const NSUInteger tmp_bytes = nrows * (NSUInteger)head_dim * (NSUInteger)nwg * sizeof(float) +
                                 nrows * (2u * (NSUInteger)nwg) * sizeof(float);

    if (!ds4_gpu_ensure_scratch_buffer(&g_flash_attn_mask_buffer,
                                         &g_flash_attn_mask_bytes,
                                         mask_bytes,
                                         "ds4_flash_attn_mask") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_kv_buffer,
                                         &g_flash_attn_kv_bytes,
                                         kv_bytes,
                                         "ds4_flash_attn_kv") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_pad_buffer,
                                         &g_flash_attn_pad_bytes,
                                         pad_bytes,
                                         "ds4_flash_attn_pad") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_tmp_buffer,
                                         &g_flash_attn_tmp_bytes,
```<｜Assistant｜></think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Trova bug sottili e spiega quali invarianti dell'inferenza possono rompersi.

File: ds4_metal.m

```c
nsor_buffer(comp_mask) : nil;
    const uint64_t q_bytes = (uint64_t)n_head * head_dim * sizeof(float);
    const uint64_t raw_bytes = (uint64_t)raw_cap * head_dim * sizeof(float);
    const uint64_t comp_bytes = (uint64_t)n_comp * head_dim * sizeof(float);
    const uint64_t comp_mask_bytes = use_mask ? (uint64_t)n_comp * sizeof(float) : 0u;
    if (!qbuf || !rawbuf || !headsbuf || !sinks_buf ||
        (n_comp && !compbuf) ||
        (use_mask && !maskbuf) ||
        ds4_gpu_tensor_bytes(q) < q_bytes ||
        ds4_gpu_tensor_bytes(raw_kv) < raw_bytes ||
        (n_comp && ds4_gpu_tensor_bytes(comp_kv) < comp_bytes) ||
        ds4_gpu_tensor_bytes(heads) < q_bytes ||
        (use_mask && ds4_gpu_tensor_bytes(comp_mask) < comp_mask_bytes)) {
        fprintf(stderr, "ds4: Metal gathered DS4 FlashAttention received undersized buffers\n");
        return 0;
    }

    const uint32_t ncpsg = 32;
    const uint32_t nwg = 32;
    const uint32_t nsg = ds4_gpu_flash_attn_vec_nsg(n_keys, nwg, ncpsg);
    const NSUInteger row_bytes = (NSUInteger)head_dim * sizeof(float);
    const NSUInteger row_bytes_f16 = (NSUInteger)head_dim * sizeof(uint16_t);
    const NSUInteger mask_bytes = (NSUInteger)n_keys * sizeof(uint16_t);
    const NSUInteger kv_bytes = (NSUInteger)n_keys * row_bytes_f16;
    const NSUInteger pad_bytes = 2u * (NSUInteger)ncpsg * row_bytes_f16 +
                                 (NSUInteger)ncpsg * sizeof(uint16_t);
    const NSUInteger nrows = (NSUInteger)n_head;
    const NSUInteger tmp_bytes = nrows * (NSUInteger)head_dim * (NSUInteger)nwg * sizeof(float) +
                                 nrows * (2u * (NSUInteger)nwg) * sizeof(float);

    if (!ds4_gpu_ensure_scratch_buffer(&g_flash_attn_mask_buffer,
                                         &g_flash_attn_mask_bytes,
                                         mask_bytes,
                                         "ds4_flash_attn_mask") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_kv_buffer,
                                         &g_flash_attn_kv_bytes,
                                         kv_bytes,
                                         "ds4_flash_attn_kv") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_pad_buffer,
                                         &g_flash_attn_pad_bytes,
                                         pad_bytes,
                                         "ds4_flash_attn_pad") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_tmp_buffer,
                                         &g_flash_attn_tmp_bytes,
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Trova bug sottili e spiega quali invarianti dell'inferenza possono rompersi.

File: ds4_metal.m

```c
nsor_buffer(comp_mask) : nil;
    const uint64_t q_bytes = (uint64_t)n_head * head_dim * sizeof(float);
    const uint64_t raw_bytes = (uint64_t)raw_cap * head_dim * sizeof(float);
    const uint64_t comp_bytes = (uint64_t)n_comp * head_dim * sizeof(float);
    const uint64_t comp_mask_bytes = use_mask ? (uint64_t)n_comp * sizeof(float) : 0u;
    if (!qbuf || !rawbuf || !headsbuf || !sinks_buf ||
        (n_comp && !compbuf) ||
        (use_mask && !maskbuf) ||
        ds4_gpu_tensor_bytes(q) < q_bytes ||
        ds4_gpu_tensor_bytes(raw_kv) < raw_bytes ||
        (n_comp && ds4_gpu_tensor_bytes(comp_kv) < comp_bytes) ||
        ds4_gpu_tensor_bytes(heads) < q_bytes ||
        (use_mask && ds4_gpu_tensor_bytes(comp_mask) < comp_mask_bytes)) {
        fprintf(stderr, "ds4: Metal gathered DS4 FlashAttention received undersized buffers\n");
        return 0;
    }

    const uint32_t ncpsg = 32;
    const uint32_t nwg = 32;
    const uint32_t nsg = ds4_gpu_flash_attn_vec_nsg(n_keys, nwg, ncpsg);
    const NSUInteger row_bytes = (NSUInteger)head_dim * sizeof(float);
    const NSUInteger row_bytes_f16 = (NSUInteger)head_dim * sizeof(uint16_t);
    const NSUInteger mask_bytes = (NSUInteger)n_keys * sizeof(uint16_t);
    const NSUInteger kv_bytes = (NSUInteger)n_keys * row_bytes_f16;
    const NSUInteger pad_bytes = 2u * (NSUInteger)ncpsg * row_bytes_f16 +
                                 (NSUInteger)ncpsg * sizeof(uint16_t);
    const NSUInteger nrows = (NSUInteger)n_head;
    const NSUInteger tmp_bytes = nrows * (NSUInteger)head_dim * (NSUInteger)nwg * sizeof(float) +
                                 nrows * (2u * (NSUInteger)nwg) * sizeof(float);

    if (!ds4_gpu_ensure_scratch_buffer(&g_flash_attn_mask_buffer,
                                         &g_flash_attn_mask_bytes,
                                         mask_bytes,
                                         "ds4_flash_attn_mask") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_kv_buffer,
                                         &g_flash_attn_kv_bytes,
                                         kv_bytes,
                                         "ds4_flash_attn_kv") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_pad_buffer,
                                         &g_flash_attn_pad_bytes,
                                         pad_bytes,
                                         "ds4_flash_attn_pad") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_tmp_buffer,
                                         &g_flash_attn_tmp_bytes,
```<｜Assistant｜><think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Review this excerpt for correctness risks, memory lifetime issues, and performance bottlenecks.

File: ds4_metal.m

```c
"ds4_flash_attn_pad") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_tmp_buffer,
                                         &g_flash_attn_tmp_bytes,
                                         tmp_bytes,
                                         "ds4_flash_attn_tmp")) {
        return 0;
    }

    id<MTLComputePipelineState> pad_pipeline = nil;
    if ((n_keys % ncpsg) != 0) {
        pad_pipeline = ds4_gpu_get_flash_attn_pad_pipeline(true, (int32_t)ncpsg);
        if (!pad_pipeline) return 0;
    }
    id<MTLComputePipelineState> vec_pipeline =
        ds4_gpu_get_flash_attn_vec_pipeline("kernel_flash_attn_ext_vec_f16_dk512_dv512",
                                              true, true, false, false, (n_keys % ncpsg) != 0,
                                              (int32_t)head_dim,
                                              (int32_t)head_dim,
                                              (int32_t)nsg,
                                              (int32_t)nwg);
    id<MTLComputePipelineState> reduce_pipeline =
        ds4_gpu_get_flash_attn_reduce_pipeline((int32_t)head_dim, (int32_t)nwg);
    if (!vec_pipeline || !reduce_pipeline) return 0;

    id<MTLBuffer> raw_linear_buf = rawbuf;
    NSUInteger raw_linear_offset = ds4_gpu_tensor_offset(raw_kv);
    if (raw_start != 0) {
        const NSUInteger ring_bytes = (NSUInteger)n_raw * row_bytes;
        const uint32_t tail_rows = raw_cap - raw_start < n_raw ? raw_cap - raw_start : n_raw;
        const uint32_t head_rows = n_raw - tail_rows;
        if (!ds4_gpu_ensure_scratch_buffer(&g_flash_attn_ring_buffer,
                                             &g_flash_attn_ring_bytes,
                                             ring_bytes,
                                             "ds4_flash_attn_ring")) {
            return 0;
        }

        if ((tail_rows &&
             !ds4_gpu_encode_cpy_f32_f32_1d(cb,
                                              rawbuf,
                                              ds4_gpu_tensor_offset(raw_kv) + (NSUInteger)raw_start * row_bytes,
                                              g_flash_attn_ring_buffer,
                                              0,
                                              tail_rows * head_dim)) ||
            (head_rows &&
             !ds4_gpu_encode_cpy_f32_f32_1d(cb,
                                              rawbuf,
                                              ds4_gpu_tensor_offset(raw_kv),
                                              g_flash_attn_ring_buffer,
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Review this excerpt for correctness risks, memory lifetime issues, and performance bottlenecks.

File: ds4_metal.m

```c
"ds4_flash_attn_pad") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_tmp_buffer,
                                         &g_flash_attn_tmp_bytes,
                                         tmp_bytes,
                                         "ds4_flash_attn_tmp")) {
        return 0;
    }

    id<MTLComputePipelineState> pad_pipeline = nil;
    if ((n_keys % ncpsg) != 0) {
        pad_pipeline = ds4_gpu_get_flash_attn_pad_pipeline(true, (int32_t)ncpsg);
        if (!pad_pipeline) return 0;
    }
    id<MTLComputePipelineState> vec_pipeline =
        ds4_gpu_get_flash_attn_vec_pipeline("kernel_flash_attn_ext_vec_f16_dk512_dv512",
                                              true, true, false, false, (n_keys % ncpsg) != 0,
                                              (int32_t)head_dim,
                                              (int32_t)head_dim,
                                              (int32_t)nsg,
                                              (int32_t)nwg);
    id<MTLComputePipelineState> reduce_pipeline =
        ds4_gpu_get_flash_attn_reduce_pipeline((int32_t)head_dim, (int32_t)nwg);
    if (!vec_pipeline || !reduce_pipeline) return 0;

    id<MTLBuffer> raw_linear_buf = rawbuf;
    NSUInteger raw_linear_offset = ds4_gpu_tensor_offset(raw_kv);
    if (raw_start != 0) {
        const NSUInteger ring_bytes = (NSUInteger)n_raw * row_bytes;
        const uint32_t tail_rows = raw_cap - raw_start < n_raw ? raw_cap - raw_start : n_raw;
        const uint32_t head_rows = n_raw - tail_rows;
        if (!ds4_gpu_ensure_scratch_buffer(&g_flash_attn_ring_buffer,
                                             &g_flash_attn_ring_bytes,
                                             ring_bytes,
                                             "ds4_flash_attn_ring")) {
            return 0;
        }

        if ((tail_rows &&
             !ds4_gpu_encode_cpy_f32_f32_1d(cb,
                                              rawbuf,
                                              ds4_gpu_tensor_offset(raw_kv) + (NSUInteger)raw_start * row_bytes,
                                              g_flash_attn_ring_buffer,
                                              0,
                                              tail_rows * head_dim)) ||
            (head_rows &&
             !ds4_gpu_encode_cpy_f32_f32_1d(cb,
                                              rawbuf,
                                              ds4_gpu_tensor_offset(raw_kv),
                                              g_flash_attn_ring_buffer,
```<｜Assistant｜></think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Review this excerpt for correctness risks, memory lifetime issues, and performance bottlenecks.

File: ds4_metal.m

```c
"ds4_flash_attn_pad") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_tmp_buffer,
                                         &g_flash_attn_tmp_bytes,
                                         tmp_bytes,
                                         "ds4_flash_attn_tmp")) {
        return 0;
    }

    id<MTLComputePipelineState> pad_pipeline = nil;
    if ((n_keys % ncpsg) != 0) {
        pad_pipeline = ds4_gpu_get_flash_attn_pad_pipeline(true, (int32_t)ncpsg);
        if (!pad_pipeline) return 0;
    }
    id<MTLComputePipelineState> vec_pipeline =
        ds4_gpu_get_flash_attn_vec_pipeline("kernel_flash_attn_ext_vec_f16_dk512_dv512",
                                              true, true, false, false, (n_keys % ncpsg) != 0,
                                              (int32_t)head_dim,
                                              (int32_t)head_dim,
                                              (int32_t)nsg,
                                              (int32_t)nwg);
    id<MTLComputePipelineState> reduce_pipeline =
        ds4_gpu_get_flash_attn_reduce_pipeline((int32_t)head_dim, (int32_t)nwg);
    if (!vec_pipeline || !reduce_pipeline) return 0;

    id<MTLBuffer> raw_linear_buf = rawbuf;
    NSUInteger raw_linear_offset = ds4_gpu_tensor_offset(raw_kv);
    if (raw_start != 0) {
        const NSUInteger ring_bytes = (NSUInteger)n_raw * row_bytes;
        const uint32_t tail_rows = raw_cap - raw_start < n_raw ? raw_cap - raw_start : n_raw;
        const uint32_t head_rows = n_raw - tail_rows;
        if (!ds4_gpu_ensure_scratch_buffer(&g_flash_attn_ring_buffer,
                                             &g_flash_attn_ring_bytes,
                                             ring_bytes,
                                             "ds4_flash_attn_ring")) {
            return 0;
        }

        if ((tail_rows &&
             !ds4_gpu_encode_cpy_f32_f32_1d(cb,
                                              rawbuf,
                                              ds4_gpu_tensor_offset(raw_kv) + (NSUInteger)raw_start * row_bytes,
                                              g_flash_attn_ring_buffer,
                                              0,
                                              tail_rows * head_dim)) ||
            (head_rows &&
             !ds4_gpu_encode_cpy_f32_f32_1d(cb,
                                              rawbuf,
                                              ds4_gpu_tensor_offset(raw_kv),
                                              g_flash_attn_ring_buffer,
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Review this excerpt for correctness risks, memory lifetime issues, and performance bottlenecks.

File: ds4_metal.m

```c
"ds4_flash_attn_pad") ||
        !ds4_gpu_ensure_scratch_buffer(&g_flash_attn_tmp_buffer,
                                         &g_flash_attn_tmp_bytes,
                                         tmp_bytes,
                                         "ds4_flash_attn_tmp")) {
        return 0;
    }

    id<MTLComputePipelineState> pad_pipeline = nil;
    if ((n_keys % ncpsg) != 0) {
        pad_pipeline = ds4_gpu_get_flash_attn_pad_pipeline(true, (int32_t)ncpsg);
        if (!pad_pipeline) return 0;
    }
    id<MTLComputePipelineState> vec_pipeline =
        ds4_gpu_get_flash_attn_vec_pipeline("kernel_flash_attn_ext_vec_f16_dk512_dv512",
                                              true, true, false, false, (n_keys % ncpsg) != 0,
                                              (int32_t)head_dim,
                                              (int32_t)head_dim,
                                              (int32_t)nsg,
                                              (int32_t)nwg);
    id<MTLComputePipelineState> reduce_pipeline =
        ds4_gpu_get_flash_attn_reduce_pipeline((int32_t)head_dim, (int32_t)nwg);
    if (!vec_pipeline || !reduce_pipeline) return 0;

    id<MTLBuffer> raw_linear_buf = rawbuf;
    NSUInteger raw_linear_offset = ds4_gpu_tensor_offset(raw_kv);
    if (raw_start != 0) {
        const NSUInteger ring_bytes = (NSUInteger)n_raw * row_bytes;
        const uint32_t tail_rows = raw_cap - raw_start < n_raw ? raw_cap - raw_start : n_raw;
        const uint32_t head_rows = n_raw - tail_rows;
        if (!ds4_gpu_ensure_scratch_buffer(&g_flash_attn_ring_buffer,
                                             &g_flash_attn_ring_bytes,
                                             ring_bytes,
                                             "ds4_flash_attn_ring")) {
            return 0;
        }

        if ((tail_rows &&
             !ds4_gpu_encode_cpy_f32_f32_1d(cb,
                                              rawbuf,
                                              ds4_gpu_tensor_offset(raw_kv) + (NSUInteger)raw_start * row_bytes,
                                              g_flash_attn_ring_buffer,
                                              0,
                                              tail_rows * head_dim)) ||
            (head_rows &&
             !ds4_gpu_encode_cpy_f32_f32_1d(cb,
                                              rawbuf,
                                              ds4_gpu_tensor_offset(raw_kv),
                                              g_flash_attn_ring_buffer,
```<｜Assistant｜><think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Explain what this code does and identify the inference stage it belongs to.

File: ds4_metal.m

```c
rawbuf,
                                              ds4_gpu_tensor_offset(raw_kv),
                                              g_flash_attn_ring_buffer,
                                              (NSUInteger)tail_rows * row_bytes,
                                              head_rows * head_dim))) {
            return 0;
        }

        raw_linear_buf = g_flash_attn_ring_buffer;
        raw_linear_offset = 0;
    }

    if (!ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                         raw_linear_buf,
                                         raw_linear_offset,
                                         g_flash_attn_kv_buffer,
                                         0,
                                         n_raw * head_dim)) {
        return 0;
    }
    if (n_comp) {
        if (!ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                             compbuf,
                                             ds4_gpu_tensor_offset(comp_kv),
                                             g_flash_attn_kv_buffer,
                                             (NSUInteger)n_raw * row_bytes_f16,
                                             n_comp * head_dim)) {
            return 0;
        }
    }

    if (!ds4_gpu_encode_fill_f16_1d(cb, g_flash_attn_mask_buffer, 0, n_keys, 0.0f)) {
        return 0;
    }
    if (use_mask && n_comp &&
        !ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                         maskbuf,
                                         ds4_gpu_tensor_offset(comp_mask),
                                         g_flash_attn_mask_buffer,
                                         (NSUInteger)n_raw * sizeof(uint16_t),
                                         n_comp)) {
        return 0;
    }

    if ((n_keys % ncpsg) != 0) {
        ds4_gpu_flash_attn_pad_args pad_args = {
            .ne11 = (int32_t)n_keys,
            .ne_12_2 = 1,
            .ne_12_3 = 1,
            .nb11 = row_bytes_f16,
            .nb12 = (uint64_t)n_keys * row_bytes_f16,
            .nb13 = (uint64_t)n_keys * row_bytes_f16,
            .nb21 = row_bytes_f16,
            .nb22 = (uint64_t)n_keys * row_bytes_f16,
            .nb23 = (uint64_t)n_keys * row_bytes_f16,
            .ne31 = 1,
            .ne32 = 1,
            .ne33 = 1,
            .nb31 = mask_bytes,
            .nb32 = mask_bytes,
            .nb33 = mask_bytes,
        };

        id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
        [enc setComputePipelineState:pad_pipeline];
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Explain what this code does and identify the inference stage it belongs to.

File: ds4_metal.m

```c
rawbuf,
                                              ds4_gpu_tensor_offset(raw_kv),
                                              g_flash_attn_ring_buffer,
                                              (NSUInteger)tail_rows * row_bytes,
                                              head_rows * head_dim))) {
            return 0;
        }

        raw_linear_buf = g_flash_attn_ring_buffer;
        raw_linear_offset = 0;
    }

    if (!ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                         raw_linear_buf,
                                         raw_linear_offset,
                                         g_flash_attn_kv_buffer,
                                         0,
                                         n_raw * head_dim)) {
        return 0;
    }
    if (n_comp) {
        if (!ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                             compbuf,
                                             ds4_gpu_tensor_offset(comp_kv),
                                             g_flash_attn_kv_buffer,
                                             (NSUInteger)n_raw * row_bytes_f16,
                                             n_comp * head_dim)) {
            return 0;
        }
    }

    if (!ds4_gpu_encode_fill_f16_1d(cb, g_flash_attn_mask_buffer, 0, n_keys, 0.0f)) {
        return 0;
    }
    if (use_mask && n_comp &&
        !ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                         maskbuf,
                                         ds4_gpu_tensor_offset(comp_mask),
                                         g_flash_attn_mask_buffer,
                                         (NSUInteger)n_raw * sizeof(uint16_t),
                                         n_comp)) {
        return 0;
    }

    if ((n_keys % ncpsg) != 0) {
        ds4_gpu_flash_attn_pad_args pad_args = {
            .ne11 = (int32_t)n_keys,
            .ne_12_2 = 1,
            .ne_12_3 = 1,
            .nb11 = row_bytes_f16,
            .nb12 = (uint64_t)n_keys * row_bytes_f16,
            .nb13 = (uint64_t)n_keys * row_bytes_f16,
            .nb21 = row_bytes_f16,
            .nb22 = (uint64_t)n_keys * row_bytes_f16,
            .nb23 = (uint64_t)n_keys * row_bytes_f16,
            .ne31 = 1,
            .ne32 = 1,
            .ne33 = 1,
            .nb31 = mask_bytes,
            .nb32 = mask_bytes,
            .nb33 = mask_bytes,
        };

        id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
        [enc setComputePipelineState:pad_pipeline];
```<｜Assistant｜></think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Explain what this code does and identify the inference stage it belongs to.

File: ds4_metal.m

```c
rawbuf,
                                              ds4_gpu_tensor_offset(raw_kv),
                                              g_flash_attn_ring_buffer,
                                              (NSUInteger)tail_rows * row_bytes,
                                              head_rows * head_dim))) {
            return 0;
        }

        raw_linear_buf = g_flash_attn_ring_buffer;
        raw_linear_offset = 0;
    }

    if (!ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                         raw_linear_buf,
                                         raw_linear_offset,
                                         g_flash_attn_kv_buffer,
                                         0,
                                         n_raw * head_dim)) {
        return 0;
    }
    if (n_comp) {
        if (!ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                             compbuf,
                                             ds4_gpu_tensor_offset(comp_kv),
                                             g_flash_attn_kv_buffer,
                                             (NSUInteger)n_raw * row_bytes_f16,
                                             n_comp * head_dim)) {
            return 0;
        }
    }

    if (!ds4_gpu_encode_fill_f16_1d(cb, g_flash_attn_mask_buffer, 0, n_keys, 0.0f)) {
        return 0;
    }
    if (use_mask && n_comp &&
        !ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                         maskbuf,
                                         ds4_gpu_tensor_offset(comp_mask),
                                         g_flash_attn_mask_buffer,
                                         (NSUInteger)n_raw * sizeof(uint16_t),
                                         n_comp)) {
        return 0;
    }

    if ((n_keys % ncpsg) != 0) {
        ds4_gpu_flash_attn_pad_args pad_args = {
            .ne11 = (int32_t)n_keys,
            .ne_12_2 = 1,
            .ne_12_3 = 1,
            .nb11 = row_bytes_f16,
            .nb12 = (uint64_t)n_keys * row_bytes_f16,
            .nb13 = (uint64_t)n_keys * row_bytes_f16,
            .nb21 = row_bytes_f16,
            .nb22 = (uint64_t)n_keys * row_bytes_f16,
            .nb23 = (uint64_t)n_keys * row_bytes_f16,
            .ne31 = 1,
            .ne32 = 1,
            .ne33 = 1,
            .nb31 = mask_bytes,
            .nb32 = mask_bytes,
            .nb33 = mask_bytes,
        };

        id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
        [enc setComputePipelineState:pad_pipeline];
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Explain what this code does and identify the inference stage it belongs to.

File: ds4_metal.m

```c
rawbuf,
                                              ds4_gpu_tensor_offset(raw_kv),
                                              g_flash_attn_ring_buffer,
                                              (NSUInteger)tail_rows * row_bytes,
                                              head_rows * head_dim))) {
            return 0;
        }

        raw_linear_buf = g_flash_attn_ring_buffer;
        raw_linear_offset = 0;
    }

    if (!ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                         raw_linear_buf,
                                         raw_linear_offset,
                                         g_flash_attn_kv_buffer,
                                         0,
                                         n_raw * head_dim)) {
        return 0;
    }
    if (n_comp) {
        if (!ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                             compbuf,
                                             ds4_gpu_tensor_offset(comp_kv),
                                             g_flash_attn_kv_buffer,
                                             (NSUInteger)n_raw * row_bytes_f16,
                                             n_comp * head_dim)) {
            return 0;
        }
    }

    if (!ds4_gpu_encode_fill_f16_1d(cb, g_flash_attn_mask_buffer, 0, n_keys, 0.0f)) {
        return 0;
    }
    if (use_mask && n_comp &&
        !ds4_gpu_encode_cpy_f32_f16_1d(cb,
                                         maskbuf,
                                         ds4_gpu_tensor_offset(comp_mask),
                                         g_flash_attn_mask_buffer,
                                         (NSUInteger)n_raw * sizeof(uint16_t),
                                         n_comp)) {
        return 0;
    }

    if ((n_keys % ncpsg) != 0) {
        ds4_gpu_flash_attn_pad_args pad_args = {
            .ne11 = (int32_t)n_keys,
            .ne_12_2 = 1,
            .ne_12_3 = 1,
            .nb11 = row_bytes_f16,
            .nb12 = (uint64_t)n_keys * row_bytes_f16,
            .nb13 = (uint64_t)n_keys * row_bytes_f16,
            .nb21 = row_bytes_f16,
            .nb22 = (uint64_t)n_keys * row_bytes_f16,
            .nb23 = (uint64_t)n_keys * row_bytes_f16,
            .ne31 = 1,
            .ne32 = 1,
            .ne33 = 1,
            .nb31 = mask_bytes,
            .nb32 = mask_bytes,
            .nb33 = mask_bytes,
        };

        id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
        [enc setComputePipelineState:pad_pipeline];
```<｜Assistant｜><think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Suggest a minimal correctness-preserving optimization for this excerpt.

File: ds4_metal.m

```c
mask_bytes,
            .nb33 = mask_bytes,
        };

        id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
        [enc setComputePipelineState:pad_pipeline];
        [enc setBytes:&pad_args length:sizeof(pad_args) atIndex:0];
        [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:1];
        [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:2];
        [enc setBuffer:g_flash_attn_mask_buffer offset:0 atIndex:3];
        [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:4];
        [enc dispatchThreadgroups:MTLSizeMake(ncpsg, 1, 1)
             threadsPerThreadgroup:MTLSizeMake(32, 1, 1)];
        ds4_gpu_end_compute_encoder(cb, enc);
    }

    ds4_gpu_flash_attn_vec_args vec_args = {
        .ne01 = 1,
        .ne02 = (int32_t)n_head,
        .ne03 = 1,
        .nb01 = (uint64_t)n_head * row_bytes,
        .nb02 = row_bytes,
        .nb03 = (uint64_t)n_head * row_bytes,
        .ne11 = (int32_t)n_keys,
        .ne_12_2 = 1,
        .ne_12_3 = 1,
        .ns10 = (int32_t)head_dim,
        .nb11 = row_bytes_f16,
        .nb12 = (uint64_t)n_keys * row_bytes_f16,
        .nb13 = (uint64_t)n_keys * row_bytes_f16,
        .ns20 = (int32_t)head_dim,
        .nb21 = row_bytes_f16,
        .nb22 = (uint64_t)n_keys * row_bytes_f16,
        .nb23 = (uint64_t)n_keys * row_bytes_f16,
        .ne31 = 1,
        .ne32 = 1,
        .ne33 = 1,
        .nb31 = mask_bytes,
        .nb32 = mask_bytes,
        .nb33 = mask_bytes,
        .ne1 = (int32_t)n_head,
        .ne2 = 1,
        .ne3 = 1,
        .scale = 1.0f / sqrtf((float)head_dim),
        .max_bias = 0.0f,
        .m0 = 0.0f,
        .m1 = 0.0f,
        .n_head_log2 = 0,
        .logit_softcap = 0.0f,
    };

    const NSUInteger shared_elems = (ds4_gpu_align_up_ns(head_dim, 128u) +
                                     4u * ncpsg +
                                     2u * ds4_gpu_align_up_ns(head_dim, 128u)) * nsg;
    const NSUInteger shared_bytes = ds4_gpu_align_up_ns(shared_elems * (sizeof(float) / 2u), 16u);

    id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
    [enc setComputePipelineState:vec_pipeline];
    [enc setBytes:&vec_args length:sizeof(vec_args) atIndex:0];
    [enc setBuffer:qbuf offset:ds4_gpu_tensor_offset(q) atIndex:1];
    [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:2];
    [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:3];
    [enc setBuffer:g_flash_attn_mask_buffer offset:0 atIndex:4];
    [enc setBuffer:sinks_buf offset:sinks_offset atIndex:5];
    [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:6];
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Suggest a minimal correctness-preserving optimization for this excerpt.

File: ds4_metal.m

```c
mask_bytes,
            .nb33 = mask_bytes,
        };

        id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
        [enc setComputePipelineState:pad_pipeline];
        [enc setBytes:&pad_args length:sizeof(pad_args) atIndex:0];
        [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:1];
        [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:2];
        [enc setBuffer:g_flash_attn_mask_buffer offset:0 atIndex:3];
        [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:4];
        [enc dispatchThreadgroups:MTLSizeMake(ncpsg, 1, 1)
             threadsPerThreadgroup:MTLSizeMake(32, 1, 1)];
        ds4_gpu_end_compute_encoder(cb, enc);
    }

    ds4_gpu_flash_attn_vec_args vec_args = {
        .ne01 = 1,
        .ne02 = (int32_t)n_head,
        .ne03 = 1,
        .nb01 = (uint64_t)n_head * row_bytes,
        .nb02 = row_bytes,
        .nb03 = (uint64_t)n_head * row_bytes,
        .ne11 = (int32_t)n_keys,
        .ne_12_2 = 1,
        .ne_12_3 = 1,
        .ns10 = (int32_t)head_dim,
        .nb11 = row_bytes_f16,
        .nb12 = (uint64_t)n_keys * row_bytes_f16,
        .nb13 = (uint64_t)n_keys * row_bytes_f16,
        .ns20 = (int32_t)head_dim,
        .nb21 = row_bytes_f16,
        .nb22 = (uint64_t)n_keys * row_bytes_f16,
        .nb23 = (uint64_t)n_keys * row_bytes_f16,
        .ne31 = 1,
        .ne32 = 1,
        .ne33 = 1,
        .nb31 = mask_bytes,
        .nb32 = mask_bytes,
        .nb33 = mask_bytes,
        .ne1 = (int32_t)n_head,
        .ne2 = 1,
        .ne3 = 1,
        .scale = 1.0f / sqrtf((float)head_dim),
        .max_bias = 0.0f,
        .m0 = 0.0f,
        .m1 = 0.0f,
        .n_head_log2 = 0,
        .logit_softcap = 0.0f,
    };

    const NSUInteger shared_elems = (ds4_gpu_align_up_ns(head_dim, 128u) +
                                     4u * ncpsg +
                                     2u * ds4_gpu_align_up_ns(head_dim, 128u)) * nsg;
    const NSUInteger shared_bytes = ds4_gpu_align_up_ns(shared_elems * (sizeof(float) / 2u), 16u);

    id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
    [enc setComputePipelineState:vec_pipeline];
    [enc setBytes:&vec_args length:sizeof(vec_args) atIndex:0];
    [enc setBuffer:qbuf offset:ds4_gpu_tensor_offset(q) atIndex:1];
    [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:2];
    [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:3];
    [enc setBuffer:g_flash_attn_mask_buffer offset:0 atIndex:4];
    [enc setBuffer:sinks_buf offset:sinks_offset atIndex:5];
    [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:6];
```<｜Assistant｜></think>


[System] You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.

[User]
Suggest a minimal correctness-preserving optimization for this excerpt.

File: ds4_metal.m

```c
mask_bytes,
            .nb33 = mask_bytes,
        };

        id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
        [enc setComputePipelineState:pad_pipeline];
        [enc setBytes:&pad_args length:sizeof(pad_args) atIndex:0];
        [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:1];
        [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:2];
        [enc setBuffer:g_flash_attn_mask_buffer offset:0 atIndex:3];
        [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:4];
        [enc dispatchThreadgroups:MTLSizeMake(ncpsg, 1, 1)
             threadsPerThreadgroup:MTLSizeMake(32, 1, 1)];
        ds4_gpu_end_compute_encoder(cb, enc);
    }

    ds4_gpu_flash_attn_vec_args vec_args = {
        .ne01 = 1,
        .ne02 = (int32_t)n_head,
        .ne03 = 1,
        .nb01 = (uint64_t)n_head * row_bytes,
        .nb02 = row_bytes,
        .nb03 = (uint64_t)n_head * row_bytes,
        .ne11 = (int32_t)n_keys,
        .ne_12_2 = 1,
        .ne_12_3 = 1,
        .ns10 = (int32_t)head_dim,
        .nb11 = row_bytes_f16,
        .nb12 = (uint64_t)n_keys * row_bytes_f16,
        .nb13 = (uint64_t)n_keys * row_bytes_f16,
        .ns20 = (int32_t)head_dim,
        .nb21 = row_bytes_f16,
        .nb22 = (uint64_t)n_keys * row_bytes_f16,
        .nb23 = (uint64_t)n_keys * row_bytes_f16,
        .ne31 = 1,
        .ne32 = 1,
        .ne33 = 1,
        .nb31 = mask_bytes,
        .nb32 = mask_bytes,
        .nb33 = mask_bytes,
        .ne1 = (int32_t)n_head,
        .ne2 = 1,
        .ne3 = 1,
        .scale = 1.0f / sqrtf((float)head_dim),
        .max_bias = 0.0f,
        .m0 = 0.0f,
        .m1 = 0.0f,
        .n_head_log2 = 0,
        .logit_softcap = 0.0f,
    };

    const NSUInteger shared_elems = (ds4_gpu_align_up_ns(head_dim, 128u) +
                                     4u * ncpsg +
                                     2u * ds4_gpu_align_up_ns(head_dim, 128u)) * nsg;
    const NSUInteger shared_bytes = ds4_gpu_align_up_ns(shared_elems * (sizeof(float) / 2u), 16u);

    id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
    [enc setComputePipelineState:vec_pipeline];
    [enc setBytes:&vec_args length:sizeof(vec_args) atIndex:0];
    [enc setBuffer:qbuf offset:ds4_gpu_tensor_offset(q) atIndex:1];
    [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:2];
    [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:3];
    [enc setBuffer:g_flash_attn_mask_buffer offset:0 atIndex:4];
    [enc setBuffer:sinks_buf offset:sinks_offset atIndex:5];
    [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:6];
```

<｜begin▁of▁sentence｜>You are DeepSeek V4 Flash running locally. Answer accurately, preserve technical details, and use tools only when the prompt asks for tool use.<｜User｜>Suggest a minimal correctness-preserving optimization for this excerpt.

File: ds4_metal.m

```c
mask_bytes,
            .nb33 = mask_bytes,
        };

        id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
        [enc setComputePipelineState:pad_pipeline];
        [enc setBytes:&pad_args length:sizeof(pad_args) atIndex:0];
        [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:1];
        [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:2];
        [enc setBuffer:g_flash_attn_mask_buffer offset:0 atIndex:3];
        [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:4];
        [enc dispatchThreadgroups:MTLSizeMake(ncpsg, 1, 1)
             threadsPerThreadgroup:MTLSizeMake(32, 1, 1)];
        ds4_gpu_end_compute_encoder(cb, enc);
    }

    ds4_gpu_flash_attn_vec_args vec_args = {
        .ne01 = 1,
        .ne02 = (int32_t)n_head,
        .ne03 = 1,
        .nb01 = (uint64_t)n_head * row_bytes,
        .nb02 = row_bytes,
        .nb03 = (uint64_t)n_head * row_bytes,
        .ne11 = (int32_t)n_keys,
        .ne_12_2 = 1,
        .ne_12_3 = 1,
        .ns10 = (int32_t)head_dim,
        .nb11 = row_bytes_f16,
        .nb12 = (uint64_t)n_keys * row_bytes_f16,
        .nb13 = (uint64_t)n_keys * row_bytes_f16,
        .ns20 = (int32_t)head_dim,
        .nb21 = row_bytes_f16,
        .nb22 = (uint64_t)n_keys * row_bytes_f16,
        .nb23 = (uint64_t)n_keys * row_bytes_f16,
        .ne31 = 1,
        .ne32 = 1,
        .ne33 = 1,
        .nb31 = mask_bytes,
        .nb32 = mask_bytes,
        .nb33 = mask_bytes,
        .ne1 = (int32_t)n_head,
        .ne2 = 1,
        .ne3 = 1,
        .scale = 1.0f / sqrtf((float)head_dim),
        .max_bias = 0.0f,
        .m0 = 0.0f,
        .m1 = 0.0f,
        .n_head_log2 = 0,
        .logit_softcap = 0.0f,
    };

    const NSUInteger shared_elems = (ds4_gpu_align_up_ns(head_dim, 128u) +
                                     4u * ncpsg +
                                     2u * ds4_gpu_align_up_ns(head_dim, 128u)) * nsg;
    const NSUInteger shared_bytes = ds4_gpu_align_up_ns(shared_elems * (sizeof(float) / 2u), 16u);

    id<MTLComputeCommandEncoder> enc = ds4_gpu_compute_encoder(cb);
    [enc setComputePipelineState:vec_pipeline];
    [enc setBytes:&vec_args length:sizeof(vec_args) atIndex:0];
    [enc setBuffer:qbuf offset:ds4_gpu_tensor_offset(q) atIndex:1];
    [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:2];
    [enc setBuffer:g_flash_attn_kv_buffer offset:0 atIndex:3];
    [enc setBuffer:g_flash_attn_mask_buffer offset:0 atIndex:4];
    [enc setBuffer:sinks_buf offset:sinks_offset atIndex:5];
    [enc setBuffer:g_flash_attn_pad_buffer offset:0 atIndex:6];
```<｜Assistant｜><think>