[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.c

```c
vld1_s8(iq2xxs_signs[((aux)[1] >>  7) & 127]));      \
                const int8x16_t sgn1 = vcombine_s8(vld1_s8(iq2xxs_signs[((aux)[1] >> 14) & 127]),       \
                                                   vld1_s8(iq2xxs_signs[((aux)[1] >> 21) & 127]));      \
                const int8x16_t sgn2 = vcombine_s8(vld1_s8(iq2xxs_signs[((aux)[3] >>  0) & 127]),       \
                                                   vld1_s8(iq2xxs_signs[((aux)[3] >>  7) & 127]));      \
                const int8x16_t sgn3 = vcombine_s8(vld1_s8(iq2xxs_signs[((aux)[3] >> 14) & 127]),       \
                                                   vld1_s8(iq2xxs_signs[((aux)[3] >> 21) & 127]));      \
                u0 = vmulq_s8(u0, sgn0);                                                               \
                u1 = vmulq_s8(u1, sgn1);                                                               \
                u2 = vmulq_s8(u2, sgn2);                                                               \
                u3 = vmulq_s8(u3, sgn3);                                                               \
                const int32x4_t p1 = vdotq_s32(vdotq_s32(vdupq_n_s32(0), u0, q8b.val[0]), u1, q8b.val[1]); \
                const int32x4_t p2 = vdotq_s32(vdotq_s32(vdupq_n_s32(0), u2, q8b.val[2]), u3, q8b.val[3]); \
                (accum_a) += (float)vaddvq_s32(p1) * (0.5f + (float)((aux)[1] >> 28));                  \
                (accum_b) += (float)vaddvq_s32(p2) * (0.5f + (float)((aux)[3] >> 28));                  \
            } while (0)

            DS4_IQ2_PAIR_DOT(aux0, a0, sum01, sum02);
            DS4_IQ2_PAIR_DOT(aux1, a1, sum11, sum12);

#undef DS4_IQ2_PAIR_DOT
        }

        total0 += d0 * (sum01 + sum02);
        total1 += d1 * (sum11 + sum12);
    }

    *s0 = 0.25f * total0;
    *s1 = 0.25f * total1;
#else
    ds4_vec_dot_iq2_xxs_q8_K(n, s0, x0, y);
    ds4_vec_dot_iq2_xxs_q8_K(n, s1, x1, y);
#endif
}

typedef struct {
    ds4_tensor *hc_attn_fn;
    ds4_tensor *hc_attn_scale;
    ds4_tensor *hc_attn_base;
    ds4_tensor *attn_norm;
    ds4_tensor *attn_q_a;
    ds4_tensor *attn_q_a_norm;
    ds4_tensor *attn_q_b;
    ds4_tensor *attn_kv;
    ds4_tensor *attn_kv_a_norm;
    ds4_tensor *attn_sinks;
    ds4_tensor *attn_output_a;
    ds4_tensor *attn_output_b;
    ds4_tensor *attn_compressor_ape;
    ds4_tensor *attn_compressor_kv;
    ds4_tensor *attn_compressor_gate;
    ds4_tensor *attn_compressor_norm;
    ds4_tensor *indexer_attn_q_b;
    ds4_tensor *indexer_proj;
    ds4_tensor *indexer_compressor_ape;
```

<｜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.c

```c
vld1_s8(iq2xxs_signs[((aux)[1] >>  7) & 127]));      \
                const int8x16_t sgn1 = vcombine_s8(vld1_s8(iq2xxs_signs[((aux)[1] >> 14) & 127]),       \
                                                   vld1_s8(iq2xxs_signs[((aux)[1] >> 21) & 127]));      \
                const int8x16_t sgn2 = vcombine_s8(vld1_s8(iq2xxs_signs[((aux)[3] >>  0) & 127]),       \
                                                   vld1_s8(iq2xxs_signs[((aux)[3] >>  7) & 127]));      \
                const int8x16_t sgn3 = vcombine_s8(vld1_s8(iq2xxs_signs[((aux)[3] >> 14) & 127]),       \
                                                   vld1_s8(iq2xxs_signs[((aux)[3] >> 21) & 127]));      \
                u0 = vmulq_s8(u0, sgn0);                                                               \
                u1 = vmulq_s8(u1, sgn1);                                                               \
                u2 = vmulq_s8(u2, sgn2);                                                               \
                u3 = vmulq_s8(u3, sgn3);                                                               \
                const int32x4_t p1 = vdotq_s32(vdotq_s32(vdupq_n_s32(0), u0, q8b.val[0]), u1, q8b.val[1]); \
                const int32x4_t p2 = vdotq_s32(vdotq_s32(vdupq_n_s32(0), u2, q8b.val[2]), u3, q8b.val[3]); \
                (accum_a) += (float)vaddvq_s32(p1) * (0.5f + (float)((aux)[1] >> 28));                  \
                (accum_b) += (float)vaddvq_s32(p2) * (0.5f + (float)((aux)[3] >> 28));                  \
            } while (0)

            DS4_IQ2_PAIR_DOT(aux0, a0, sum01, sum02);
            DS4_IQ2_PAIR_DOT(aux1, a1, sum11, sum12);

#undef DS4_IQ2_PAIR_DOT
        }

        total0 += d0 * (sum01 + sum02);
        total1 += d1 * (sum11 + sum12);
    }

    *s0 = 0.25f * total0;
    *s1 = 0.25f * total1;
#else
    ds4_vec_dot_iq2_xxs_q8_K(n, s0, x0, y);
    ds4_vec_dot_iq2_xxs_q8_K(n, s1, x1, y);
#endif
}

typedef struct {
    ds4_tensor *hc_attn_fn;
    ds4_tensor *hc_attn_scale;
    ds4_tensor *hc_attn_base;
    ds4_tensor *attn_norm;
    ds4_tensor *attn_q_a;
    ds4_tensor *attn_q_a_norm;
    ds4_tensor *attn_q_b;
    ds4_tensor *attn_kv;
    ds4_tensor *attn_kv_a_norm;
    ds4_tensor *attn_sinks;
    ds4_tensor *attn_output_a;
    ds4_tensor *attn_output_b;
    ds4_tensor *attn_compressor_ape;
    ds4_tensor *attn_compressor_kv;
    ds4_tensor *attn_compressor_gate;
    ds4_tensor *attn_compressor_norm;
    ds4_tensor *indexer_attn_q_b;
    ds4_tensor *indexer_proj;
    ds4_tensor *indexer_compressor_ape;
```<｜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.c

```c
vld1_s8(iq2xxs_signs[((aux)[1] >>  7) & 127]));      \
                const int8x16_t sgn1 = vcombine_s8(vld1_s8(iq2xxs_signs[((aux)[1] >> 14) & 127]),       \
                                                   vld1_s8(iq2xxs_signs[((aux)[1] >> 21) & 127]));      \
                const int8x16_t sgn2 = vcombine_s8(vld1_s8(iq2xxs_signs[((aux)[3] >>  0) & 127]),       \
                                                   vld1_s8(iq2xxs_signs[((aux)[3] >>  7) & 127]));      \
                const int8x16_t sgn3 = vcombine_s8(vld1_s8(iq2xxs_signs[((aux)[3] >> 14) & 127]),       \
                                                   vld1_s8(iq2xxs_signs[((aux)[3] >> 21) & 127]));      \
                u0 = vmulq_s8(u0, sgn0);                                                               \
                u1 = vmulq_s8(u1, sgn1);                                                               \
                u2 = vmulq_s8(u2, sgn2);                                                               \
                u3 = vmulq_s8(u3, sgn3);                                                               \
                const int32x4_t p1 = vdotq_s32(vdotq_s32(vdupq_n_s32(0), u0, q8b.val[0]), u1, q8b.val[1]); \
                const int32x4_t p2 = vdotq_s32(vdotq_s32(vdupq_n_s32(0), u2, q8b.val[2]), u3, q8b.val[3]); \
                (accum_a) += (float)vaddvq_s32(p1) * (0.5f + (float)((aux)[1] >> 28));                  \
                (accum_b) += (float)vaddvq_s32(p2) * (0.5f + (float)((aux)[3] >> 28));                  \
            } while (0)

            DS4_IQ2_PAIR_DOT(aux0, a0, sum01, sum02);
            DS4_IQ2_PAIR_DOT(aux1, a1, sum11, sum12);

#undef DS4_IQ2_PAIR_DOT
        }

        total0 += d0 * (sum01 + sum02);
        total1 += d1 * (sum11 + sum12);
    }

    *s0 = 0.25f * total0;
    *s1 = 0.25f * total1;
#else
    ds4_vec_dot_iq2_xxs_q8_K(n, s0, x0, y);
    ds4_vec_dot_iq2_xxs_q8_K(n, s1, x1, y);
#endif
}

typedef struct {
    ds4_tensor *hc_attn_fn;
    ds4_tensor *hc_attn_scale;
    ds4_tensor *hc_attn_base;
    ds4_tensor *attn_norm;
    ds4_tensor *attn_q_a;
    ds4_tensor *attn_q_a_norm;
    ds4_tensor *attn_q_b;
    ds4_tensor *attn_kv;
    ds4_tensor *attn_kv_a_norm;
    ds4_tensor *attn_sinks;
    ds4_tensor *attn_output_a;
    ds4_tensor *attn_output_b;
    ds4_tensor *attn_compressor_ape;
    ds4_tensor *attn_compressor_kv;
    ds4_tensor *attn_compressor_gate;
    ds4_tensor *attn_compressor_norm;
    ds4_tensor *indexer_attn_q_b;
    ds4_tensor *indexer_proj;
    ds4_tensor *indexer_compressor_ape;
```

<｜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.c

```c
vld1_s8(iq2xxs_signs[((aux)[1] >>  7) & 127]));      \
                const int8x16_t sgn1 = vcombine_s8(vld1_s8(iq2xxs_signs[((aux)[1] >> 14) & 127]),       \
                                                   vld1_s8(iq2xxs_signs[((aux)[1] >> 21) & 127]));      \
                const int8x16_t sgn2 = vcombine_s8(vld1_s8(iq2xxs_signs[((aux)[3] >>  0) & 127]),       \
                                                   vld1_s8(iq2xxs_signs[((aux)[3] >>  7) & 127]));      \
                const int8x16_t sgn3 = vcombine_s8(vld1_s8(iq2xxs_signs[((aux)[3] >> 14) & 127]),       \
                                                   vld1_s8(iq2xxs_signs[((aux)[3] >> 21) & 127]));      \
                u0 = vmulq_s8(u0, sgn0);                                                               \
                u1 = vmulq_s8(u1, sgn1);                                                               \
                u2 = vmulq_s8(u2, sgn2);                                                               \
                u3 = vmulq_s8(u3, sgn3);                                                               \
                const int32x4_t p1 = vdotq_s32(vdotq_s32(vdupq_n_s32(0), u0, q8b.val[0]), u1, q8b.val[1]); \
                const int32x4_t p2 = vdotq_s32(vdotq_s32(vdupq_n_s32(0), u2, q8b.val[2]), u3, q8b.val[3]); \
                (accum_a) += (float)vaddvq_s32(p1) * (0.5f + (float)((aux)[1] >> 28));                  \
                (accum_b) += (float)vaddvq_s32(p2) * (0.5f + (float)((aux)[3] >> 28));                  \
            } while (0)

            DS4_IQ2_PAIR_DOT(aux0, a0, sum01, sum02);
            DS4_IQ2_PAIR_DOT(aux1, a1, sum11, sum12);

#undef DS4_IQ2_PAIR_DOT
        }

        total0 += d0 * (sum01 + sum02);
        total1 += d1 * (sum11 + sum12);
    }

    *s0 = 0.25f * total0;
    *s1 = 0.25f * total1;
#else
    ds4_vec_dot_iq2_xxs_q8_K(n, s0, x0, y);
    ds4_vec_dot_iq2_xxs_q8_K(n, s1, x1, y);
#endif
}

typedef struct {
    ds4_tensor *hc_attn_fn;
    ds4_tensor *hc_attn_scale;
    ds4_tensor *hc_attn_base;
    ds4_tensor *attn_norm;
    ds4_tensor *attn_q_a;
    ds4_tensor *attn_q_a_norm;
    ds4_tensor *attn_q_b;
    ds4_tensor *attn_kv;
    ds4_tensor *attn_kv_a_norm;
    ds4_tensor *attn_sinks;
    ds4_tensor *attn_output_a;
    ds4_tensor *attn_output_b;
    ds4_tensor *attn_compressor_ape;
    ds4_tensor *attn_compressor_kv;
    ds4_tensor *attn_compressor_gate;
    ds4_tensor *attn_compressor_norm;
    ds4_tensor *indexer_attn_q_b;
    ds4_tensor *indexer_proj;
    ds4_tensor *indexer_compressor_ape;
```<｜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.c

```c
t32_t raw_live = session_raw_live_rows(g, checkpoint_len);
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        bytes += (uint64_t)raw_live * DS4_N_HEAD_DIM * sizeof(float);
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;
        bytes += (uint64_t)g->layer_n_comp[il] * DS4_N_HEAD_DIM * sizeof(float);
        bytes += layer_attn_state_bytes(ratio);
        bytes += layer_attn_state_bytes(ratio);
        if (ratio == 4) {
            bytes += (uint64_t)g->layer_n_index_comp[il] * DS4_N_INDEXER_HEAD_DIM * sizeof(float);
            bytes += layer_index_state_bytes(ratio);
            bytes += layer_index_state_bytes(ratio);
        }
    }
    return bytes;
}

/* Metal tensors are copied through a fixed-size CPU buffer.  We do not mmap the
 * cache file and we do not allocate a second graph-sized blob just to serialize
 * it; both would be poor fits for this very large model. */
static int payload_write_tensor_span(FILE *fp, const ds4_gpu_tensor *tensor,
                                     uint64_t offset, uint64_t bytes,
                                     uint8_t *buf, size_t cap, char *err, size_t errlen) {
    if (!tensor || offset > ds4_gpu_tensor_bytes(tensor) ||
        bytes > ds4_gpu_tensor_bytes(tensor) - offset)
    {
        payload_set_err(err, errlen, "session tensor is smaller than the payload");
        return 1;
    }
    uint64_t done = 0;
    while (done < bytes) {
        const size_t n = bytes - done > (uint64_t)cap ? cap : (size_t)(bytes - done);
        if (ds4_gpu_tensor_read(tensor, offset + done, buf, n) == 0) {
            payload_set_err(err, errlen, "failed to read Metal session tensor");
            return 1;
        }
        if (payload_write_bytes(fp, buf, n, err, errlen) != 0) return 1;
        done += n;
    }
    return 0;
}

static int payload_read_tensor_span(FILE *fp, ds4_gpu_tensor *tensor,
                                    uint64_t offset, uint64_t bytes,
                                    uint8_t *buf, size_t cap, uint64_t *remaining,
                                    char *err, size_t errlen) {
    if (!tensor || offset > ds4_gpu_tensor_bytes(tensor) ||
        bytes > ds4_gpu_tensor_bytes(tensor) - offset)
    {
        payload_set_err(err, errlen, "session tensor is smaller than the payload");
        return 1;
    }
    uint64_t done = 0;
    while (done < bytes) {
        const size_t n = bytes - done > (uint64_t)cap ? cap : (size_t)(bytes - done);
        if (payload_read_bytes(fp, buf, n, remaining, err, errlen) != 0) return 1;
```

<｜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.c

```c
t32_t raw_live = session_raw_live_rows(g, checkpoint_len);
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        bytes += (uint64_t)raw_live * DS4_N_HEAD_DIM * sizeof(float);
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;
        bytes += (uint64_t)g->layer_n_comp[il] * DS4_N_HEAD_DIM * sizeof(float);
        bytes += layer_attn_state_bytes(ratio);
        bytes += layer_attn_state_bytes(ratio);
        if (ratio == 4) {
            bytes += (uint64_t)g->layer_n_index_comp[il] * DS4_N_INDEXER_HEAD_DIM * sizeof(float);
            bytes += layer_index_state_bytes(ratio);
            bytes += layer_index_state_bytes(ratio);
        }
    }
    return bytes;
}

/* Metal tensors are copied through a fixed-size CPU buffer.  We do not mmap the
 * cache file and we do not allocate a second graph-sized blob just to serialize
 * it; both would be poor fits for this very large model. */
static int payload_write_tensor_span(FILE *fp, const ds4_gpu_tensor *tensor,
                                     uint64_t offset, uint64_t bytes,
                                     uint8_t *buf, size_t cap, char *err, size_t errlen) {
    if (!tensor || offset > ds4_gpu_tensor_bytes(tensor) ||
        bytes > ds4_gpu_tensor_bytes(tensor) - offset)
    {
        payload_set_err(err, errlen, "session tensor is smaller than the payload");
        return 1;
    }
    uint64_t done = 0;
    while (done < bytes) {
        const size_t n = bytes - done > (uint64_t)cap ? cap : (size_t)(bytes - done);
        if (ds4_gpu_tensor_read(tensor, offset + done, buf, n) == 0) {
            payload_set_err(err, errlen, "failed to read Metal session tensor");
            return 1;
        }
        if (payload_write_bytes(fp, buf, n, err, errlen) != 0) return 1;
        done += n;
    }
    return 0;
}

static int payload_read_tensor_span(FILE *fp, ds4_gpu_tensor *tensor,
                                    uint64_t offset, uint64_t bytes,
                                    uint8_t *buf, size_t cap, uint64_t *remaining,
                                    char *err, size_t errlen) {
    if (!tensor || offset > ds4_gpu_tensor_bytes(tensor) ||
        bytes > ds4_gpu_tensor_bytes(tensor) - offset)
    {
        payload_set_err(err, errlen, "session tensor is smaller than the payload");
        return 1;
    }
    uint64_t done = 0;
    while (done < bytes) {
        const size_t n = bytes - done > (uint64_t)cap ? cap : (size_t)(bytes - done);
        if (payload_read_bytes(fp, buf, n, remaining, err, errlen) != 0) return 1;
```<｜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.c

```c
t32_t raw_live = session_raw_live_rows(g, checkpoint_len);
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        bytes += (uint64_t)raw_live * DS4_N_HEAD_DIM * sizeof(float);
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;
        bytes += (uint64_t)g->layer_n_comp[il] * DS4_N_HEAD_DIM * sizeof(float);
        bytes += layer_attn_state_bytes(ratio);
        bytes += layer_attn_state_bytes(ratio);
        if (ratio == 4) {
            bytes += (uint64_t)g->layer_n_index_comp[il] * DS4_N_INDEXER_HEAD_DIM * sizeof(float);
            bytes += layer_index_state_bytes(ratio);
            bytes += layer_index_state_bytes(ratio);
        }
    }
    return bytes;
}

/* Metal tensors are copied through a fixed-size CPU buffer.  We do not mmap the
 * cache file and we do not allocate a second graph-sized blob just to serialize
 * it; both would be poor fits for this very large model. */
static int payload_write_tensor_span(FILE *fp, const ds4_gpu_tensor *tensor,
                                     uint64_t offset, uint64_t bytes,
                                     uint8_t *buf, size_t cap, char *err, size_t errlen) {
    if (!tensor || offset > ds4_gpu_tensor_bytes(tensor) ||
        bytes > ds4_gpu_tensor_bytes(tensor) - offset)
    {
        payload_set_err(err, errlen, "session tensor is smaller than the payload");
        return 1;
    }
    uint64_t done = 0;
    while (done < bytes) {
        const size_t n = bytes - done > (uint64_t)cap ? cap : (size_t)(bytes - done);
        if (ds4_gpu_tensor_read(tensor, offset + done, buf, n) == 0) {
            payload_set_err(err, errlen, "failed to read Metal session tensor");
            return 1;
        }
        if (payload_write_bytes(fp, buf, n, err, errlen) != 0) return 1;
        done += n;
    }
    return 0;
}

static int payload_read_tensor_span(FILE *fp, ds4_gpu_tensor *tensor,
                                    uint64_t offset, uint64_t bytes,
                                    uint8_t *buf, size_t cap, uint64_t *remaining,
                                    char *err, size_t errlen) {
    if (!tensor || offset > ds4_gpu_tensor_bytes(tensor) ||
        bytes > ds4_gpu_tensor_bytes(tensor) - offset)
    {
        payload_set_err(err, errlen, "session tensor is smaller than the payload");
        return 1;
    }
    uint64_t done = 0;
    while (done < bytes) {
        const size_t n = bytes - done > (uint64_t)cap ? cap : (size_t)(bytes - done);
        if (payload_read_bytes(fp, buf, n, remaining, err, errlen) != 0) return 1;
```

<｜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.c

```c
t32_t raw_live = session_raw_live_rows(g, checkpoint_len);
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        bytes += (uint64_t)raw_live * DS4_N_HEAD_DIM * sizeof(float);
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;
        bytes += (uint64_t)g->layer_n_comp[il] * DS4_N_HEAD_DIM * sizeof(float);
        bytes += layer_attn_state_bytes(ratio);
        bytes += layer_attn_state_bytes(ratio);
        if (ratio == 4) {
            bytes += (uint64_t)g->layer_n_index_comp[il] * DS4_N_INDEXER_HEAD_DIM * sizeof(float);
            bytes += layer_index_state_bytes(ratio);
            bytes += layer_index_state_bytes(ratio);
        }
    }
    return bytes;
}

/* Metal tensors are copied through a fixed-size CPU buffer.  We do not mmap the
 * cache file and we do not allocate a second graph-sized blob just to serialize
 * it; both would be poor fits for this very large model. */
static int payload_write_tensor_span(FILE *fp, const ds4_gpu_tensor *tensor,
                                     uint64_t offset, uint64_t bytes,
                                     uint8_t *buf, size_t cap, char *err, size_t errlen) {
    if (!tensor || offset > ds4_gpu_tensor_bytes(tensor) ||
        bytes > ds4_gpu_tensor_bytes(tensor) - offset)
    {
        payload_set_err(err, errlen, "session tensor is smaller than the payload");
        return 1;
    }
    uint64_t done = 0;
    while (done < bytes) {
        const size_t n = bytes - done > (uint64_t)cap ? cap : (size_t)(bytes - done);
        if (ds4_gpu_tensor_read(tensor, offset + done, buf, n) == 0) {
            payload_set_err(err, errlen, "failed to read Metal session tensor");
            return 1;
        }
        if (payload_write_bytes(fp, buf, n, err, errlen) != 0) return 1;
        done += n;
    }
    return 0;
}

static int payload_read_tensor_span(FILE *fp, ds4_gpu_tensor *tensor,
                                    uint64_t offset, uint64_t bytes,
                                    uint8_t *buf, size_t cap, uint64_t *remaining,
                                    char *err, size_t errlen) {
    if (!tensor || offset > ds4_gpu_tensor_bytes(tensor) ||
        bytes > ds4_gpu_tensor_bytes(tensor) - offset)
    {
        payload_set_err(err, errlen, "session tensor is smaller than the payload");
        return 1;
    }
    uint64_t done = 0;
    while (done < bytes) {
        const size_t n = bytes - done > (uint64_t)cap ? cap : (size_t)(bytes - done);
        if (payload_read_bytes(fp, buf, n, remaining, err, errlen) != 0) return 1;
```<｜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.c

```c
< bytes) {
        const size_t n = bytes - done > (uint64_t)cap ? cap : (size_t)(bytes - done);
        if (payload_read_bytes(fp, buf, n, remaining, err, errlen) != 0) return 1;
        if (ds4_gpu_tensor_write(tensor, offset + done, buf, n) == 0) {
            payload_set_err(err, errlen, "failed to restore Metal session tensor");
            return 1;
        }
        done += n;
    }
    return 0;
}
#endif

static bool ds4_session_is_cpu(const ds4_session *s) {
    return s && s->engine && s->engine->backend == DS4_BACKEND_CPU;
}

static uint32_t session_cpu_raw_live_rows(const ds4_session *s) {
    if (!s || !s->checkpoint_valid) return 0;
    uint32_t rows = ds4_default_raw_cap((uint32_t)s->ctx_size);
    if (rows > (uint32_t)s->checkpoint.len) rows = (uint32_t)s->checkpoint.len;
    return rows;
}

static uint32_t session_cpu_comp_cap(const ds4_session *s) {
    if (!s) return 0;
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
        if (layer->compress_ratio == 4) return layer->comp_cap;
    }
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
        if (layer->compress_ratio != 0) return layer->comp_cap;
    }
    return (uint32_t)s->ctx_size;
}

static uint64_t session_cpu_payload_live_tensor_bytes(const ds4_session *s) {
    uint64_t bytes = 0;
    const uint32_t raw_live = session_cpu_raw_live_rows(s);
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
        bytes += (uint64_t)raw_live * DS4_N_HEAD_DIM * sizeof(float);
        const uint32_t ratio = layer->compress_ratio;
        if (ratio == 0) continue;
        bytes += (uint64_t)layer->n_comp * DS4_N_HEAD_DIM * sizeof(float);
        bytes += layer_attn_state_bytes(ratio);
        bytes += layer_attn_state_bytes(ratio);
        if (ratio == 4) {
            bytes += (uint64_t)layer->n_index_comp * DS4_N_INDEXER_HEAD_DIM * sizeof(float);
            bytes += layer_index_state_bytes(ratio);
            bytes += layer_index_state_bytes(ratio);
        }
    }
    return bytes;
}

static void session_cpu_reset_cache(ds4_session *s) {
    kv_cache_free(&s->cpu_cache);
    kv_cache_init(&s->cpu_cache, (uint32_t)s->ctx_size, 0);
}

int ds4_engine_routed_quant_bits(ds4_engine *e) {
    if (!e) return 0;
    const ds4_tensor *gate = e->weights.layer[0].ffn_gate_exps;
    if (!gate) return 0;
    return gate->type == DS4_TENSOR_Q4_K ? 4 : 2;
}

bool ds4_engine_has_mtp(ds4_engine *e) {
```

<｜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.c

```c
< bytes) {
        const size_t n = bytes - done > (uint64_t)cap ? cap : (size_t)(bytes - done);
        if (payload_read_bytes(fp, buf, n, remaining, err, errlen) != 0) return 1;
        if (ds4_gpu_tensor_write(tensor, offset + done, buf, n) == 0) {
            payload_set_err(err, errlen, "failed to restore Metal session tensor");
            return 1;
        }
        done += n;
    }
    return 0;
}
#endif

static bool ds4_session_is_cpu(const ds4_session *s) {
    return s && s->engine && s->engine->backend == DS4_BACKEND_CPU;
}

static uint32_t session_cpu_raw_live_rows(const ds4_session *s) {
    if (!s || !s->checkpoint_valid) return 0;
    uint32_t rows = ds4_default_raw_cap((uint32_t)s->ctx_size);
    if (rows > (uint32_t)s->checkpoint.len) rows = (uint32_t)s->checkpoint.len;
    return rows;
}

static uint32_t session_cpu_comp_cap(const ds4_session *s) {
    if (!s) return 0;
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
        if (layer->compress_ratio == 4) return layer->comp_cap;
    }
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
        if (layer->compress_ratio != 0) return layer->comp_cap;
    }
    return (uint32_t)s->ctx_size;
}

static uint64_t session_cpu_payload_live_tensor_bytes(const ds4_session *s) {
    uint64_t bytes = 0;
    const uint32_t raw_live = session_cpu_raw_live_rows(s);
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
        bytes += (uint64_t)raw_live * DS4_N_HEAD_DIM * sizeof(float);
        const uint32_t ratio = layer->compress_ratio;
        if (ratio == 0) continue;
        bytes += (uint64_t)layer->n_comp * DS4_N_HEAD_DIM * sizeof(float);
        bytes += layer_attn_state_bytes(ratio);
        bytes += layer_attn_state_bytes(ratio);
        if (ratio == 4) {
            bytes += (uint64_t)layer->n_index_comp * DS4_N_INDEXER_HEAD_DIM * sizeof(float);
            bytes += layer_index_state_bytes(ratio);
            bytes += layer_index_state_bytes(ratio);
        }
    }
    return bytes;
}

static void session_cpu_reset_cache(ds4_session *s) {
    kv_cache_free(&s->cpu_cache);
    kv_cache_init(&s->cpu_cache, (uint32_t)s->ctx_size, 0);
}

int ds4_engine_routed_quant_bits(ds4_engine *e) {
    if (!e) return 0;
    const ds4_tensor *gate = e->weights.layer[0].ffn_gate_exps;
    if (!gate) return 0;
    return gate->type == DS4_TENSOR_Q4_K ? 4 : 2;
}

bool ds4_engine_has_mtp(ds4_engine *e) {
```<｜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.c

```c
< bytes) {
        const size_t n = bytes - done > (uint64_t)cap ? cap : (size_t)(bytes - done);
        if (payload_read_bytes(fp, buf, n, remaining, err, errlen) != 0) return 1;
        if (ds4_gpu_tensor_write(tensor, offset + done, buf, n) == 0) {
            payload_set_err(err, errlen, "failed to restore Metal session tensor");
            return 1;
        }
        done += n;
    }
    return 0;
}
#endif

static bool ds4_session_is_cpu(const ds4_session *s) {
    return s && s->engine && s->engine->backend == DS4_BACKEND_CPU;
}

static uint32_t session_cpu_raw_live_rows(const ds4_session *s) {
    if (!s || !s->checkpoint_valid) return 0;
    uint32_t rows = ds4_default_raw_cap((uint32_t)s->ctx_size);
    if (rows > (uint32_t)s->checkpoint.len) rows = (uint32_t)s->checkpoint.len;
    return rows;
}

static uint32_t session_cpu_comp_cap(const ds4_session *s) {
    if (!s) return 0;
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
        if (layer->compress_ratio == 4) return layer->comp_cap;
    }
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
        if (layer->compress_ratio != 0) return layer->comp_cap;
    }
    return (uint32_t)s->ctx_size;
}

static uint64_t session_cpu_payload_live_tensor_bytes(const ds4_session *s) {
    uint64_t bytes = 0;
    const uint32_t raw_live = session_cpu_raw_live_rows(s);
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
        bytes += (uint64_t)raw_live * DS4_N_HEAD_DIM * sizeof(float);
        const uint32_t ratio = layer->compress_ratio;
        if (ratio == 0) continue;
        bytes += (uint64_t)layer->n_comp * DS4_N_HEAD_DIM * sizeof(float);
        bytes += layer_attn_state_bytes(ratio);
        bytes += layer_attn_state_bytes(ratio);
        if (ratio == 4) {
            bytes += (uint64_t)layer->n_index_comp * DS4_N_INDEXER_HEAD_DIM * sizeof(float);
            bytes += layer_index_state_bytes(ratio);
            bytes += layer_index_state_bytes(ratio);
        }
    }
    return bytes;
}

static void session_cpu_reset_cache(ds4_session *s) {
    kv_cache_free(&s->cpu_cache);
    kv_cache_init(&s->cpu_cache, (uint32_t)s->ctx_size, 0);
}

int ds4_engine_routed_quant_bits(ds4_engine *e) {
    if (!e) return 0;
    const ds4_tensor *gate = e->weights.layer[0].ffn_gate_exps;
    if (!gate) return 0;
    return gate->type == DS4_TENSOR_Q4_K ? 4 : 2;
}

bool ds4_engine_has_mtp(ds4_engine *e) {
```

<｜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.c

```c
< bytes) {
        const size_t n = bytes - done > (uint64_t)cap ? cap : (size_t)(bytes - done);
        if (payload_read_bytes(fp, buf, n, remaining, err, errlen) != 0) return 1;
        if (ds4_gpu_tensor_write(tensor, offset + done, buf, n) == 0) {
            payload_set_err(err, errlen, "failed to restore Metal session tensor");
            return 1;
        }
        done += n;
    }
    return 0;
}
#endif

static bool ds4_session_is_cpu(const ds4_session *s) {
    return s && s->engine && s->engine->backend == DS4_BACKEND_CPU;
}

static uint32_t session_cpu_raw_live_rows(const ds4_session *s) {
    if (!s || !s->checkpoint_valid) return 0;
    uint32_t rows = ds4_default_raw_cap((uint32_t)s->ctx_size);
    if (rows > (uint32_t)s->checkpoint.len) rows = (uint32_t)s->checkpoint.len;
    return rows;
}

static uint32_t session_cpu_comp_cap(const ds4_session *s) {
    if (!s) return 0;
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
        if (layer->compress_ratio == 4) return layer->comp_cap;
    }
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
        if (layer->compress_ratio != 0) return layer->comp_cap;
    }
    return (uint32_t)s->ctx_size;
}

static uint64_t session_cpu_payload_live_tensor_bytes(const ds4_session *s) {
    uint64_t bytes = 0;
    const uint32_t raw_live = session_cpu_raw_live_rows(s);
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
        bytes += (uint64_t)raw_live * DS4_N_HEAD_DIM * sizeof(float);
        const uint32_t ratio = layer->compress_ratio;
        if (ratio == 0) continue;
        bytes += (uint64_t)layer->n_comp * DS4_N_HEAD_DIM * sizeof(float);
        bytes += layer_attn_state_bytes(ratio);
        bytes += layer_attn_state_bytes(ratio);
        if (ratio == 4) {
            bytes += (uint64_t)layer->n_index_comp * DS4_N_INDEXER_HEAD_DIM * sizeof(float);
            bytes += layer_index_state_bytes(ratio);
            bytes += layer_index_state_bytes(ratio);
        }
    }
    return bytes;
}

static void session_cpu_reset_cache(ds4_session *s) {
    kv_cache_free(&s->cpu_cache);
    kv_cache_init(&s->cpu_cache, (uint32_t)s->ctx_size, 0);
}

int ds4_engine_routed_quant_bits(ds4_engine *e) {
    if (!e) return 0;
    const ds4_tensor *gate = e->weights.layer[0].ffn_gate_exps;
    if (!gate) return 0;
    return gate->type == DS4_TENSOR_Q4_K ? 4 : 2;
}

bool ds4_engine_has_mtp(ds4_engine *e) {
```<｜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.c

```c
const ds4_tensor *gate = e->weights.layer[0].ffn_gate_exps;
    if (!gate) return 0;
    return gate->type == DS4_TENSOR_Q4_K ? 4 : 2;
}

bool ds4_engine_has_mtp(ds4_engine *e) {
    return e && e->backend != DS4_BACKEND_CPU && e->mtp_ready;
}

int ds4_engine_mtp_draft_tokens(ds4_engine *e) {
    return e && e->backend != DS4_BACKEND_CPU && e->mtp_ready ? e->mtp_draft_tokens : 0;
}

const ds4_tokens *ds4_session_tokens(ds4_session *s) {
    return s ? &s->checkpoint : NULL;
}

#ifndef DS4_NO_GPU
typedef struct {
    uint32_t n_comp[DS4_N_LAYER];
    uint32_t n_index_comp[DS4_N_LAYER];
    uint32_t mtp_n_raw;
} ds4_spec_frontier;

static void spec_frontier_free(ds4_spec_frontier *f) {
    if (!f) return;
    memset(f, 0, sizeof(*f));
}

static bool spec_frontier_snapshot(ds4_spec_frontier *f, ds4_session *s) {
    memset(f, 0, sizeof(*f));
    ds4_gpu_graph *g = &s->graph;
    f->mtp_n_raw = g->mtp_n_raw;

    bool ok = ds4_gpu_begin_commands() != 0;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        f->n_comp[il] = g->layer_n_comp[il];
        f->n_index_comp[il] = g->layer_n_index_comp[il];
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;
        const uint64_t ab = ds4_gpu_tensor_bytes(g->layer_attn_state_kv[il]);
        ok = ds4_gpu_tensor_copy(g->spec_attn_state_kv[il], 0,
                                   g->layer_attn_state_kv[il], 0, ab) != 0 &&
             ds4_gpu_tensor_copy(g->spec_attn_state_score[il], 0,
                                   g->layer_attn_state_score[il], 0, ab) != 0;
        if (ratio == 4) {
            const uint64_t ib = ds4_gpu_tensor_bytes(g->layer_index_state_kv[il]);
            ok = ok &&
                 ds4_gpu_tensor_copy(g->spec_index_state_kv[il], 0,
                                       g->layer_index_state_kv[il], 0, ib) != 0 &&
                 ds4_gpu_tensor_copy(g->spec_index_state_score[il], 0,
                                       g->layer_index_state_score[il], 0, ib) != 0;
        }
    }
    if (ok) ok = ds4_gpu_end_commands() != 0;
    else (void)ds4_gpu_synchronize();
    if (ok) return true;

    spec_frontier_free(f);
    return false;
}

static bool spec_frontier_restore(ds4_spec_frontier *f, ds4_session *s) {
    ds4_gpu_graph *g = &s->graph;
    bool ok = ds4_gpu_begin_commands() != 0;
    g->mtp_n_raw = f->mtp_n_raw;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        g->layer_n_comp[il] = f->n_comp[il];
        g->layer_n_index_comp[il] = f->n_index_comp[il];
```

<｜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.c

```c
const ds4_tensor *gate = e->weights.layer[0].ffn_gate_exps;
    if (!gate) return 0;
    return gate->type == DS4_TENSOR_Q4_K ? 4 : 2;
}

bool ds4_engine_has_mtp(ds4_engine *e) {
    return e && e->backend != DS4_BACKEND_CPU && e->mtp_ready;
}

int ds4_engine_mtp_draft_tokens(ds4_engine *e) {
    return e && e->backend != DS4_BACKEND_CPU && e->mtp_ready ? e->mtp_draft_tokens : 0;
}

const ds4_tokens *ds4_session_tokens(ds4_session *s) {
    return s ? &s->checkpoint : NULL;
}

#ifndef DS4_NO_GPU
typedef struct {
    uint32_t n_comp[DS4_N_LAYER];
    uint32_t n_index_comp[DS4_N_LAYER];
    uint32_t mtp_n_raw;
} ds4_spec_frontier;

static void spec_frontier_free(ds4_spec_frontier *f) {
    if (!f) return;
    memset(f, 0, sizeof(*f));
}

static bool spec_frontier_snapshot(ds4_spec_frontier *f, ds4_session *s) {
    memset(f, 0, sizeof(*f));
    ds4_gpu_graph *g = &s->graph;
    f->mtp_n_raw = g->mtp_n_raw;

    bool ok = ds4_gpu_begin_commands() != 0;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        f->n_comp[il] = g->layer_n_comp[il];
        f->n_index_comp[il] = g->layer_n_index_comp[il];
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;
        const uint64_t ab = ds4_gpu_tensor_bytes(g->layer_attn_state_kv[il]);
        ok = ds4_gpu_tensor_copy(g->spec_attn_state_kv[il], 0,
                                   g->layer_attn_state_kv[il], 0, ab) != 0 &&
             ds4_gpu_tensor_copy(g->spec_attn_state_score[il], 0,
                                   g->layer_attn_state_score[il], 0, ab) != 0;
        if (ratio == 4) {
            const uint64_t ib = ds4_gpu_tensor_bytes(g->layer_index_state_kv[il]);
            ok = ok &&
                 ds4_gpu_tensor_copy(g->spec_index_state_kv[il], 0,
                                       g->layer_index_state_kv[il], 0, ib) != 0 &&
                 ds4_gpu_tensor_copy(g->spec_index_state_score[il], 0,
                                       g->layer_index_state_score[il], 0, ib) != 0;
        }
    }
    if (ok) ok = ds4_gpu_end_commands() != 0;
    else (void)ds4_gpu_synchronize();
    if (ok) return true;

    spec_frontier_free(f);
    return false;
}

static bool spec_frontier_restore(ds4_spec_frontier *f, ds4_session *s) {
    ds4_gpu_graph *g = &s->graph;
    bool ok = ds4_gpu_begin_commands() != 0;
    g->mtp_n_raw = f->mtp_n_raw;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        g->layer_n_comp[il] = f->n_comp[il];
        g->layer_n_index_comp[il] = f->n_index_comp[il];
```<｜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.c

```c
const ds4_tensor *gate = e->weights.layer[0].ffn_gate_exps;
    if (!gate) return 0;
    return gate->type == DS4_TENSOR_Q4_K ? 4 : 2;
}

bool ds4_engine_has_mtp(ds4_engine *e) {
    return e && e->backend != DS4_BACKEND_CPU && e->mtp_ready;
}

int ds4_engine_mtp_draft_tokens(ds4_engine *e) {
    return e && e->backend != DS4_BACKEND_CPU && e->mtp_ready ? e->mtp_draft_tokens : 0;
}

const ds4_tokens *ds4_session_tokens(ds4_session *s) {
    return s ? &s->checkpoint : NULL;
}

#ifndef DS4_NO_GPU
typedef struct {
    uint32_t n_comp[DS4_N_LAYER];
    uint32_t n_index_comp[DS4_N_LAYER];
    uint32_t mtp_n_raw;
} ds4_spec_frontier;

static void spec_frontier_free(ds4_spec_frontier *f) {
    if (!f) return;
    memset(f, 0, sizeof(*f));
}

static bool spec_frontier_snapshot(ds4_spec_frontier *f, ds4_session *s) {
    memset(f, 0, sizeof(*f));
    ds4_gpu_graph *g = &s->graph;
    f->mtp_n_raw = g->mtp_n_raw;

    bool ok = ds4_gpu_begin_commands() != 0;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        f->n_comp[il] = g->layer_n_comp[il];
        f->n_index_comp[il] = g->layer_n_index_comp[il];
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;
        const uint64_t ab = ds4_gpu_tensor_bytes(g->layer_attn_state_kv[il]);
        ok = ds4_gpu_tensor_copy(g->spec_attn_state_kv[il], 0,
                                   g->layer_attn_state_kv[il], 0, ab) != 0 &&
             ds4_gpu_tensor_copy(g->spec_attn_state_score[il], 0,
                                   g->layer_attn_state_score[il], 0, ab) != 0;
        if (ratio == 4) {
            const uint64_t ib = ds4_gpu_tensor_bytes(g->layer_index_state_kv[il]);
            ok = ok &&
                 ds4_gpu_tensor_copy(g->spec_index_state_kv[il], 0,
                                       g->layer_index_state_kv[il], 0, ib) != 0 &&
                 ds4_gpu_tensor_copy(g->spec_index_state_score[il], 0,
                                       g->layer_index_state_score[il], 0, ib) != 0;
        }
    }
    if (ok) ok = ds4_gpu_end_commands() != 0;
    else (void)ds4_gpu_synchronize();
    if (ok) return true;

    spec_frontier_free(f);
    return false;
}

static bool spec_frontier_restore(ds4_spec_frontier *f, ds4_session *s) {
    ds4_gpu_graph *g = &s->graph;
    bool ok = ds4_gpu_begin_commands() != 0;
    g->mtp_n_raw = f->mtp_n_raw;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        g->layer_n_comp[il] = f->n_comp[il];
        g->layer_n_index_comp[il] = f->n_index_comp[il];
```

<｜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.c

```c
const ds4_tensor *gate = e->weights.layer[0].ffn_gate_exps;
    if (!gate) return 0;
    return gate->type == DS4_TENSOR_Q4_K ? 4 : 2;
}

bool ds4_engine_has_mtp(ds4_engine *e) {
    return e && e->backend != DS4_BACKEND_CPU && e->mtp_ready;
}

int ds4_engine_mtp_draft_tokens(ds4_engine *e) {
    return e && e->backend != DS4_BACKEND_CPU && e->mtp_ready ? e->mtp_draft_tokens : 0;
}

const ds4_tokens *ds4_session_tokens(ds4_session *s) {
    return s ? &s->checkpoint : NULL;
}

#ifndef DS4_NO_GPU
typedef struct {
    uint32_t n_comp[DS4_N_LAYER];
    uint32_t n_index_comp[DS4_N_LAYER];
    uint32_t mtp_n_raw;
} ds4_spec_frontier;

static void spec_frontier_free(ds4_spec_frontier *f) {
    if (!f) return;
    memset(f, 0, sizeof(*f));
}

static bool spec_frontier_snapshot(ds4_spec_frontier *f, ds4_session *s) {
    memset(f, 0, sizeof(*f));
    ds4_gpu_graph *g = &s->graph;
    f->mtp_n_raw = g->mtp_n_raw;

    bool ok = ds4_gpu_begin_commands() != 0;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        f->n_comp[il] = g->layer_n_comp[il];
        f->n_index_comp[il] = g->layer_n_index_comp[il];
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;
        const uint64_t ab = ds4_gpu_tensor_bytes(g->layer_attn_state_kv[il]);
        ok = ds4_gpu_tensor_copy(g->spec_attn_state_kv[il], 0,
                                   g->layer_attn_state_kv[il], 0, ab) != 0 &&
             ds4_gpu_tensor_copy(g->spec_attn_state_score[il], 0,
                                   g->layer_attn_state_score[il], 0, ab) != 0;
        if (ratio == 4) {
            const uint64_t ib = ds4_gpu_tensor_bytes(g->layer_index_state_kv[il]);
            ok = ok &&
                 ds4_gpu_tensor_copy(g->spec_index_state_kv[il], 0,
                                       g->layer_index_state_kv[il], 0, ib) != 0 &&
                 ds4_gpu_tensor_copy(g->spec_index_state_score[il], 0,
                                       g->layer_index_state_score[il], 0, ib) != 0;
        }
    }
    if (ok) ok = ds4_gpu_end_commands() != 0;
    else (void)ds4_gpu_synchronize();
    if (ok) return true;

    spec_frontier_free(f);
    return false;
}

static bool spec_frontier_restore(ds4_spec_frontier *f, ds4_session *s) {
    ds4_gpu_graph *g = &s->graph;
    bool ok = ds4_gpu_begin_commands() != 0;
    g->mtp_n_raw = f->mtp_n_raw;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        g->layer_n_comp[il] = f->n_comp[il];
        g->layer_n_index_comp[il] = f->n_index_comp[il];
```<｜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.c

```c
_raw = f->mtp_n_raw;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        g->layer_n_comp[il] = f->n_comp[il];
        g->layer_n_index_comp[il] = f->n_index_comp[il];
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;
        const uint64_t ab = ds4_gpu_tensor_bytes(g->layer_attn_state_kv[il]);
        ok = ds4_gpu_tensor_copy(g->layer_attn_state_kv[il], 0,
                                   g->spec_attn_state_kv[il], 0, ab) != 0 &&
             ds4_gpu_tensor_copy(g->layer_attn_state_score[il], 0,
                                   g->spec_attn_state_score[il], 0, ab) != 0;
        if (ok && ratio == 4) {
            const uint64_t ib = ds4_gpu_tensor_bytes(g->layer_index_state_kv[il]);
            ok = ds4_gpu_tensor_copy(g->layer_index_state_kv[il], 0,
                                       g->spec_index_state_kv[il], 0, ib) != 0 &&
                 ds4_gpu_tensor_copy(g->layer_index_state_score[il], 0,
                                       g->spec_index_state_score[il], 0, ib) != 0;
        }
    }
    if (ok) ok = ds4_gpu_end_commands() != 0;
    else (void)ds4_gpu_synchronize();
    return ok;
}

/* Commit the prefix-1 state captured by the N=2 speculative verifier.
 *
 * The verifier has already advanced every layer through both draft tokens.  On
 * a one-token accept the append-only compressed caches can keep the second
 * speculative row as invisible garbage, but the compressor frontiers and row
 * counters must be rewound to the exact state after draft[0].  This is the
 * cheap partial-accept path: copy a few small per-layer frontiers instead of
 * restoring the whole prefix and replaying a one-token target decode. */
static bool spec_frontier_commit_prefix1(ds4_session *s) {
    ds4_gpu_graph *g = &s->graph;
    bool ok = ds4_gpu_begin_commands() != 0;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;

        g->layer_n_comp[il] = g->spec_prefix1_n_comp[il];
        const uint64_t ab = ds4_gpu_tensor_bytes(g->layer_attn_state_kv[il]);
        ok = ds4_gpu_tensor_copy(g->layer_attn_state_kv[il], 0,
                                   g->spec_prefix1_attn_state_kv[il], 0, ab) != 0 &&
             ds4_gpu_tensor_copy(g->layer_attn_state_score[il], 0,
                                   g->spec_prefix1_attn_state_score[il], 0, ab) != 0;
        if (ok && ratio == 4) {
            g->layer_n_index_comp[il] = g->spec_prefix1_n_index_comp[il];
```

<｜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.c

```c
_raw = f->mtp_n_raw;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        g->layer_n_comp[il] = f->n_comp[il];
        g->layer_n_index_comp[il] = f->n_index_comp[il];
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;
        const uint64_t ab = ds4_gpu_tensor_bytes(g->layer_attn_state_kv[il]);
        ok = ds4_gpu_tensor_copy(g->layer_attn_state_kv[il], 0,
                                   g->spec_attn_state_kv[il], 0, ab) != 0 &&
             ds4_gpu_tensor_copy(g->layer_attn_state_score[il], 0,
                                   g->spec_attn_state_score[il], 0, ab) != 0;
        if (ok && ratio == 4) {
            const uint64_t ib = ds4_gpu_tensor_bytes(g->layer_index_state_kv[il]);
            ok = ds4_gpu_tensor_copy(g->layer_index_state_kv[il], 0,
                                       g->spec_index_state_kv[il], 0, ib) != 0 &&
                 ds4_gpu_tensor_copy(g->layer_index_state_score[il], 0,
                                       g->spec_index_state_score[il], 0, ib) != 0;
        }
    }
    if (ok) ok = ds4_gpu_end_commands() != 0;
    else (void)ds4_gpu_synchronize();
    return ok;
}

/* Commit the prefix-1 state captured by the N=2 speculative verifier.
 *
 * The verifier has already advanced every layer through both draft tokens.  On
 * a one-token accept the append-only compressed caches can keep the second
 * speculative row as invisible garbage, but the compressor frontiers and row
 * counters must be rewound to the exact state after draft[0].  This is the
 * cheap partial-accept path: copy a few small per-layer frontiers instead of
 * restoring the whole prefix and replaying a one-token target decode. */
static bool spec_frontier_commit_prefix1(ds4_session *s) {
    ds4_gpu_graph *g = &s->graph;
    bool ok = ds4_gpu_begin_commands() != 0;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;

        g->layer_n_comp[il] = g->spec_prefix1_n_comp[il];
        const uint64_t ab = ds4_gpu_tensor_bytes(g->layer_attn_state_kv[il]);
        ok = ds4_gpu_tensor_copy(g->layer_attn_state_kv[il], 0,
                                   g->spec_prefix1_attn_state_kv[il], 0, ab) != 0 &&
             ds4_gpu_tensor_copy(g->layer_attn_state_score[il], 0,
                                   g->spec_prefix1_attn_state_score[il], 0, ab) != 0;
        if (ok && ratio == 4) {
            g->layer_n_index_comp[il] = g->spec_prefix1_n_index_comp[il];
```<｜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.c

```c
_raw = f->mtp_n_raw;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        g->layer_n_comp[il] = f->n_comp[il];
        g->layer_n_index_comp[il] = f->n_index_comp[il];
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;
        const uint64_t ab = ds4_gpu_tensor_bytes(g->layer_attn_state_kv[il]);
        ok = ds4_gpu_tensor_copy(g->layer_attn_state_kv[il], 0,
                                   g->spec_attn_state_kv[il], 0, ab) != 0 &&
             ds4_gpu_tensor_copy(g->layer_attn_state_score[il], 0,
                                   g->spec_attn_state_score[il], 0, ab) != 0;
        if (ok && ratio == 4) {
            const uint64_t ib = ds4_gpu_tensor_bytes(g->layer_index_state_kv[il]);
            ok = ds4_gpu_tensor_copy(g->layer_index_state_kv[il], 0,
                                       g->spec_index_state_kv[il], 0, ib) != 0 &&
                 ds4_gpu_tensor_copy(g->layer_index_state_score[il], 0,
                                       g->spec_index_state_score[il], 0, ib) != 0;
        }
    }
    if (ok) ok = ds4_gpu_end_commands() != 0;
    else (void)ds4_gpu_synchronize();
    return ok;
}

/* Commit the prefix-1 state captured by the N=2 speculative verifier.
 *
 * The verifier has already advanced every layer through both draft tokens.  On
 * a one-token accept the append-only compressed caches can keep the second
 * speculative row as invisible garbage, but the compressor frontiers and row
 * counters must be rewound to the exact state after draft[0].  This is the
 * cheap partial-accept path: copy a few small per-layer frontiers instead of
 * restoring the whole prefix and replaying a one-token target decode. */
static bool spec_frontier_commit_prefix1(ds4_session *s) {
    ds4_gpu_graph *g = &s->graph;
    bool ok = ds4_gpu_begin_commands() != 0;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;

        g->layer_n_comp[il] = g->spec_prefix1_n_comp[il];
        const uint64_t ab = ds4_gpu_tensor_bytes(g->layer_attn_state_kv[il]);
        ok = ds4_gpu_tensor_copy(g->layer_attn_state_kv[il], 0,
                                   g->spec_prefix1_attn_state_kv[il], 0, ab) != 0 &&
             ds4_gpu_tensor_copy(g->layer_attn_state_score[il], 0,
                                   g->spec_prefix1_attn_state_score[il], 0, ab) != 0;
        if (ok && ratio == 4) {
            g->layer_n_index_comp[il] = g->spec_prefix1_n_index_comp[il];
```

<｜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.c

```c
_raw = f->mtp_n_raw;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        g->layer_n_comp[il] = f->n_comp[il];
        g->layer_n_index_comp[il] = f->n_index_comp[il];
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;
        const uint64_t ab = ds4_gpu_tensor_bytes(g->layer_attn_state_kv[il]);
        ok = ds4_gpu_tensor_copy(g->layer_attn_state_kv[il], 0,
                                   g->spec_attn_state_kv[il], 0, ab) != 0 &&
             ds4_gpu_tensor_copy(g->layer_attn_state_score[il], 0,
                                   g->spec_attn_state_score[il], 0, ab) != 0;
        if (ok && ratio == 4) {
            const uint64_t ib = ds4_gpu_tensor_bytes(g->layer_index_state_kv[il]);
            ok = ds4_gpu_tensor_copy(g->layer_index_state_kv[il], 0,
                                       g->spec_index_state_kv[il], 0, ib) != 0 &&
                 ds4_gpu_tensor_copy(g->layer_index_state_score[il], 0,
                                       g->spec_index_state_score[il], 0, ib) != 0;
        }
    }
    if (ok) ok = ds4_gpu_end_commands() != 0;
    else (void)ds4_gpu_synchronize();
    return ok;
}

/* Commit the prefix-1 state captured by the N=2 speculative verifier.
 *
 * The verifier has already advanced every layer through both draft tokens.  On
 * a one-token accept the append-only compressed caches can keep the second
 * speculative row as invisible garbage, but the compressor frontiers and row
 * counters must be rewound to the exact state after draft[0].  This is the
 * cheap partial-accept path: copy a few small per-layer frontiers instead of
 * restoring the whole prefix and replaying a one-token target decode. */
static bool spec_frontier_commit_prefix1(ds4_session *s) {
    ds4_gpu_graph *g = &s->graph;
    bool ok = ds4_gpu_begin_commands() != 0;
    for (uint32_t il = 0; ok && il < DS4_N_LAYER; il++) {
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (ratio == 0) continue;

        g->layer_n_comp[il] = g->spec_prefix1_n_comp[il];
        const uint64_t ab = ds4_gpu_tensor_bytes(g->layer_attn_state_kv[il]);
        ok = ds4_gpu_tensor_copy(g->layer_attn_state_kv[il], 0,
                                   g->spec_prefix1_attn_state_kv[il], 0, ab) != 0 &&
             ds4_gpu_tensor_copy(g->layer_attn_state_score[il], 0,
                                   g->spec_prefix1_attn_state_score[il], 0, ab) != 0;
        if (ok && ratio == 4) {
            g->layer_n_index_comp[il] = g->spec_prefix1_n_index_comp[il];
```<｜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.c

```c
g->spec_prefix1_attn_state_score[il], 0, ab) != 0;
        if (ok && ratio == 4) {
            g->layer_n_index_comp[il] = g->spec_prefix1_n_index_comp[il];
            const uint64_t ib = ds4_gpu_tensor_bytes(g->layer_index_state_kv[il]);
            ok = ds4_gpu_tensor_copy(g->layer_index_state_kv[il], 0,
                                       g->spec_prefix1_index_state_kv[il], 0, ib) != 0 &&
                 ds4_gpu_tensor_copy(g->layer_index_state_score[il], 0,
                                       g->spec_prefix1_index_state_score[il], 0, ib) != 0;
        }
    }
    if (ok) ok = ds4_gpu_end_commands() != 0;
    else (void)ds4_gpu_synchronize();
    return ok;
}
#endif

uint64_t ds4_session_payload_bytes(ds4_session *s) {
    if (!s || !s->checkpoint_valid) return 0;
    if (ds4_session_is_cpu(s)) {
        uint64_t bytes = (uint64_t)DS4_SESSION_PAYLOAD_U32_FIELDS * sizeof(uint32_t);
        bytes += (uint64_t)s->checkpoint.len * sizeof(uint32_t);
        bytes += (uint64_t)DS4_N_VOCAB * sizeof(float);
        bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
        bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
        bytes += session_cpu_payload_live_tensor_bytes(s);
        return bytes;
    }
#ifdef DS4_NO_GPU
    return 0;
#else
    const ds4_gpu_graph *g = &s->graph;
    uint64_t bytes = (uint64_t)DS4_SESSION_PAYLOAD_U32_FIELDS * sizeof(uint32_t);
    bytes += (uint64_t)s->checkpoint.len * sizeof(uint32_t);
    bytes += (uint64_t)DS4_N_VOCAB * sizeof(float);
    bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
    bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
    bytes += session_payload_live_tensor_bytes(g, (uint32_t)s->checkpoint.len);
    return bytes;
#endif
}

int ds4_session_save_payload(ds4_session *s, FILE *fp, char *err, size_t errlen) {
    if (!s || !fp || !s->checkpoint_valid) {
        payload_set_err(err, errlen, "session has no valid checkpoint to save");
        return 1;
    }
    if (ds4_session_is_cpu(s)) {
        const uint32_t raw_live = session_cpu_raw_live_rows(s);
        const uint32_t raw_cap = ds4_default_raw_cap((uint32_t)s->ctx_size);
        const uint32_t comp_cap = session_cpu_comp_cap(s);
        uint32_t header[DS4_SESSION_PAYLOAD_U32_FIELDS] = {
            DS4_SESSION_PAYLOAD_MAGIC,
            DS4_SESSION_PAYLOAD_VERSION,
            (uint32_t)s->ctx_size,
            s->prefill_cap,
            raw_cap,
            raw_cap,
            comp_cap,
            (uint32_t)s->checkpoint.len,
            DS4_N_LAYER,
            DS4_N_HEAD_DIM,
```

<｜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.c

```c
g->spec_prefix1_attn_state_score[il], 0, ab) != 0;
        if (ok && ratio == 4) {
            g->layer_n_index_comp[il] = g->spec_prefix1_n_index_comp[il];
            const uint64_t ib = ds4_gpu_tensor_bytes(g->layer_index_state_kv[il]);
            ok = ds4_gpu_tensor_copy(g->layer_index_state_kv[il], 0,
                                       g->spec_prefix1_index_state_kv[il], 0, ib) != 0 &&
                 ds4_gpu_tensor_copy(g->layer_index_state_score[il], 0,
                                       g->spec_prefix1_index_state_score[il], 0, ib) != 0;
        }
    }
    if (ok) ok = ds4_gpu_end_commands() != 0;
    else (void)ds4_gpu_synchronize();
    return ok;
}
#endif

uint64_t ds4_session_payload_bytes(ds4_session *s) {
    if (!s || !s->checkpoint_valid) return 0;
    if (ds4_session_is_cpu(s)) {
        uint64_t bytes = (uint64_t)DS4_SESSION_PAYLOAD_U32_FIELDS * sizeof(uint32_t);
        bytes += (uint64_t)s->checkpoint.len * sizeof(uint32_t);
        bytes += (uint64_t)DS4_N_VOCAB * sizeof(float);
        bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
        bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
        bytes += session_cpu_payload_live_tensor_bytes(s);
        return bytes;
    }
#ifdef DS4_NO_GPU
    return 0;
#else
    const ds4_gpu_graph *g = &s->graph;
    uint64_t bytes = (uint64_t)DS4_SESSION_PAYLOAD_U32_FIELDS * sizeof(uint32_t);
    bytes += (uint64_t)s->checkpoint.len * sizeof(uint32_t);
    bytes += (uint64_t)DS4_N_VOCAB * sizeof(float);
    bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
    bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
    bytes += session_payload_live_tensor_bytes(g, (uint32_t)s->checkpoint.len);
    return bytes;
#endif
}

int ds4_session_save_payload(ds4_session *s, FILE *fp, char *err, size_t errlen) {
    if (!s || !fp || !s->checkpoint_valid) {
        payload_set_err(err, errlen, "session has no valid checkpoint to save");
        return 1;
    }
    if (ds4_session_is_cpu(s)) {
        const uint32_t raw_live = session_cpu_raw_live_rows(s);
        const uint32_t raw_cap = ds4_default_raw_cap((uint32_t)s->ctx_size);
        const uint32_t comp_cap = session_cpu_comp_cap(s);
        uint32_t header[DS4_SESSION_PAYLOAD_U32_FIELDS] = {
            DS4_SESSION_PAYLOAD_MAGIC,
            DS4_SESSION_PAYLOAD_VERSION,
            (uint32_t)s->ctx_size,
            s->prefill_cap,
            raw_cap,
            raw_cap,
            comp_cap,
            (uint32_t)s->checkpoint.len,
            DS4_N_LAYER,
            DS4_N_HEAD_DIM,
```<｜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.c

```c
g->spec_prefix1_attn_state_score[il], 0, ab) != 0;
        if (ok && ratio == 4) {
            g->layer_n_index_comp[il] = g->spec_prefix1_n_index_comp[il];
            const uint64_t ib = ds4_gpu_tensor_bytes(g->layer_index_state_kv[il]);
            ok = ds4_gpu_tensor_copy(g->layer_index_state_kv[il], 0,
                                       g->spec_prefix1_index_state_kv[il], 0, ib) != 0 &&
                 ds4_gpu_tensor_copy(g->layer_index_state_score[il], 0,
                                       g->spec_prefix1_index_state_score[il], 0, ib) != 0;
        }
    }
    if (ok) ok = ds4_gpu_end_commands() != 0;
    else (void)ds4_gpu_synchronize();
    return ok;
}
#endif

uint64_t ds4_session_payload_bytes(ds4_session *s) {
    if (!s || !s->checkpoint_valid) return 0;
    if (ds4_session_is_cpu(s)) {
        uint64_t bytes = (uint64_t)DS4_SESSION_PAYLOAD_U32_FIELDS * sizeof(uint32_t);
        bytes += (uint64_t)s->checkpoint.len * sizeof(uint32_t);
        bytes += (uint64_t)DS4_N_VOCAB * sizeof(float);
        bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
        bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
        bytes += session_cpu_payload_live_tensor_bytes(s);
        return bytes;
    }
#ifdef DS4_NO_GPU
    return 0;
#else
    const ds4_gpu_graph *g = &s->graph;
    uint64_t bytes = (uint64_t)DS4_SESSION_PAYLOAD_U32_FIELDS * sizeof(uint32_t);
    bytes += (uint64_t)s->checkpoint.len * sizeof(uint32_t);
    bytes += (uint64_t)DS4_N_VOCAB * sizeof(float);
    bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
    bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
    bytes += session_payload_live_tensor_bytes(g, (uint32_t)s->checkpoint.len);
    return bytes;
#endif
}

int ds4_session_save_payload(ds4_session *s, FILE *fp, char *err, size_t errlen) {
    if (!s || !fp || !s->checkpoint_valid) {
        payload_set_err(err, errlen, "session has no valid checkpoint to save");
        return 1;
    }
    if (ds4_session_is_cpu(s)) {
        const uint32_t raw_live = session_cpu_raw_live_rows(s);
        const uint32_t raw_cap = ds4_default_raw_cap((uint32_t)s->ctx_size);
        const uint32_t comp_cap = session_cpu_comp_cap(s);
        uint32_t header[DS4_SESSION_PAYLOAD_U32_FIELDS] = {
            DS4_SESSION_PAYLOAD_MAGIC,
            DS4_SESSION_PAYLOAD_VERSION,
            (uint32_t)s->ctx_size,
            s->prefill_cap,
            raw_cap,
            raw_cap,
            comp_cap,
            (uint32_t)s->checkpoint.len,
            DS4_N_LAYER,
            DS4_N_HEAD_DIM,
```

<｜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.c

```c
g->spec_prefix1_attn_state_score[il], 0, ab) != 0;
        if (ok && ratio == 4) {
            g->layer_n_index_comp[il] = g->spec_prefix1_n_index_comp[il];
            const uint64_t ib = ds4_gpu_tensor_bytes(g->layer_index_state_kv[il]);
            ok = ds4_gpu_tensor_copy(g->layer_index_state_kv[il], 0,
                                       g->spec_prefix1_index_state_kv[il], 0, ib) != 0 &&
                 ds4_gpu_tensor_copy(g->layer_index_state_score[il], 0,
                                       g->spec_prefix1_index_state_score[il], 0, ib) != 0;
        }
    }
    if (ok) ok = ds4_gpu_end_commands() != 0;
    else (void)ds4_gpu_synchronize();
    return ok;
}
#endif

uint64_t ds4_session_payload_bytes(ds4_session *s) {
    if (!s || !s->checkpoint_valid) return 0;
    if (ds4_session_is_cpu(s)) {
        uint64_t bytes = (uint64_t)DS4_SESSION_PAYLOAD_U32_FIELDS * sizeof(uint32_t);
        bytes += (uint64_t)s->checkpoint.len * sizeof(uint32_t);
        bytes += (uint64_t)DS4_N_VOCAB * sizeof(float);
        bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
        bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
        bytes += session_cpu_payload_live_tensor_bytes(s);
        return bytes;
    }
#ifdef DS4_NO_GPU
    return 0;
#else
    const ds4_gpu_graph *g = &s->graph;
    uint64_t bytes = (uint64_t)DS4_SESSION_PAYLOAD_U32_FIELDS * sizeof(uint32_t);
    bytes += (uint64_t)s->checkpoint.len * sizeof(uint32_t);
    bytes += (uint64_t)DS4_N_VOCAB * sizeof(float);
    bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
    bytes += (uint64_t)DS4_N_LAYER * sizeof(uint32_t);
    bytes += session_payload_live_tensor_bytes(g, (uint32_t)s->checkpoint.len);
    return bytes;
#endif
}

int ds4_session_save_payload(ds4_session *s, FILE *fp, char *err, size_t errlen) {
    if (!s || !fp || !s->checkpoint_valid) {
        payload_set_err(err, errlen, "session has no valid checkpoint to save");
        return 1;
    }
    if (ds4_session_is_cpu(s)) {
        const uint32_t raw_live = session_cpu_raw_live_rows(s);
        const uint32_t raw_cap = ds4_default_raw_cap((uint32_t)s->ctx_size);
        const uint32_t comp_cap = session_cpu_comp_cap(s);
        uint32_t header[DS4_SESSION_PAYLOAD_U32_FIELDS] = {
            DS4_SESSION_PAYLOAD_MAGIC,
            DS4_SESSION_PAYLOAD_VERSION,
            (uint32_t)s->ctx_size,
            s->prefill_cap,
            raw_cap,
            raw_cap,
            comp_cap,
            (uint32_t)s->checkpoint.len,
            DS4_N_LAYER,
            DS4_N_HEAD_DIM,
```<｜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.c

```c
s->prefill_cap,
            raw_cap,
            raw_cap,
            comp_cap,
            (uint32_t)s->checkpoint.len,
            DS4_N_LAYER,
            DS4_N_HEAD_DIM,
            DS4_N_INDEXER_HEAD_DIM,
            DS4_N_VOCAB,
            raw_live,
        };
        for (uint32_t i = 0; i < DS4_SESSION_PAYLOAD_U32_FIELDS; i++) {
            if (payload_write_u32(fp, header[i], err, errlen) != 0) return 1;
        }
        for (int i = 0; i < s->checkpoint.len; i++) {
            if (payload_write_u32(fp, (uint32_t)s->checkpoint.v[i], err, errlen) != 0) return 1;
        }
        if (payload_write_bytes(fp, s->logits, (uint64_t)DS4_N_VOCAB * sizeof(float), err, errlen) != 0) return 1;
        for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
            if (payload_write_u32(fp, s->cpu_cache.layer[il].n_comp, err, errlen) != 0) return 1;
        }
        for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
            if (payload_write_u32(fp, s->cpu_cache.layer[il].n_index_comp, err, errlen) != 0) return 1;
        }
        for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
            const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
            if (raw_live > layer->n_raw) {
                payload_set_err(err, errlen, "CPU session raw cache has fewer live rows than checkpoint");
                return 1;
            }
            const uint32_t raw_start = layer->n_raw - raw_live;
            if (payload_write_bytes(fp,
                                    layer->raw_kv + (uint64_t)raw_start * DS4_N_HEAD_DIM,
                                    (uint64_t)raw_live * DS4_N_HEAD_DIM * sizeof(float),
                                    err,
                                    errlen) != 0) return 1;
            const uint32_t ratio = layer->compress_ratio;
            if (ratio == 0) continue;
            if (payload_write_bytes(fp,
                                    layer->attn_comp_kv,
                                    (uint64_t)layer->n_comp * DS4_N_HEAD_DIM * sizeof(float),
                                    err,
                                    errlen) != 0) return 1;
            if (payload_write_bytes(fp, layer->attn_state_kv, layer_attn_state_bytes(ratio), err, errlen) != 0) return 1;
            if (payload_write_bytes(fp, layer->attn_state_score, layer_attn_state_bytes(ratio), err, errlen) != 0) return 1;
            if (ratio == 4) {
                if (payload_write_bytes(fp,
                                        layer->index_comp_kv,
```

<｜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.c

```c
s->prefill_cap,
            raw_cap,
            raw_cap,
            comp_cap,
            (uint32_t)s->checkpoint.len,
            DS4_N_LAYER,
            DS4_N_HEAD_DIM,
            DS4_N_INDEXER_HEAD_DIM,
            DS4_N_VOCAB,
            raw_live,
        };
        for (uint32_t i = 0; i < DS4_SESSION_PAYLOAD_U32_FIELDS; i++) {
            if (payload_write_u32(fp, header[i], err, errlen) != 0) return 1;
        }
        for (int i = 0; i < s->checkpoint.len; i++) {
            if (payload_write_u32(fp, (uint32_t)s->checkpoint.v[i], err, errlen) != 0) return 1;
        }
        if (payload_write_bytes(fp, s->logits, (uint64_t)DS4_N_VOCAB * sizeof(float), err, errlen) != 0) return 1;
        for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
            if (payload_write_u32(fp, s->cpu_cache.layer[il].n_comp, err, errlen) != 0) return 1;
        }
        for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
            if (payload_write_u32(fp, s->cpu_cache.layer[il].n_index_comp, err, errlen) != 0) return 1;
        }
        for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
            const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
            if (raw_live > layer->n_raw) {
                payload_set_err(err, errlen, "CPU session raw cache has fewer live rows than checkpoint");
                return 1;
            }
            const uint32_t raw_start = layer->n_raw - raw_live;
            if (payload_write_bytes(fp,
                                    layer->raw_kv + (uint64_t)raw_start * DS4_N_HEAD_DIM,
                                    (uint64_t)raw_live * DS4_N_HEAD_DIM * sizeof(float),
                                    err,
                                    errlen) != 0) return 1;
            const uint32_t ratio = layer->compress_ratio;
            if (ratio == 0) continue;
            if (payload_write_bytes(fp,
                                    layer->attn_comp_kv,
                                    (uint64_t)layer->n_comp * DS4_N_HEAD_DIM * sizeof(float),
                                    err,
                                    errlen) != 0) return 1;
            if (payload_write_bytes(fp, layer->attn_state_kv, layer_attn_state_bytes(ratio), err, errlen) != 0) return 1;
            if (payload_write_bytes(fp, layer->attn_state_score, layer_attn_state_bytes(ratio), err, errlen) != 0) return 1;
            if (ratio == 4) {
                if (payload_write_bytes(fp,
                                        layer->index_comp_kv,
```<｜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.c

```c
s->prefill_cap,
            raw_cap,
            raw_cap,
            comp_cap,
            (uint32_t)s->checkpoint.len,
            DS4_N_LAYER,
            DS4_N_HEAD_DIM,
            DS4_N_INDEXER_HEAD_DIM,
            DS4_N_VOCAB,
            raw_live,
        };
        for (uint32_t i = 0; i < DS4_SESSION_PAYLOAD_U32_FIELDS; i++) {
            if (payload_write_u32(fp, header[i], err, errlen) != 0) return 1;
        }
        for (int i = 0; i < s->checkpoint.len; i++) {
            if (payload_write_u32(fp, (uint32_t)s->checkpoint.v[i], err, errlen) != 0) return 1;
        }
        if (payload_write_bytes(fp, s->logits, (uint64_t)DS4_N_VOCAB * sizeof(float), err, errlen) != 0) return 1;
        for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
            if (payload_write_u32(fp, s->cpu_cache.layer[il].n_comp, err, errlen) != 0) return 1;
        }
        for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
            if (payload_write_u32(fp, s->cpu_cache.layer[il].n_index_comp, err, errlen) != 0) return 1;
        }
        for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
            const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
            if (raw_live > layer->n_raw) {
                payload_set_err(err, errlen, "CPU session raw cache has fewer live rows than checkpoint");
                return 1;
            }
            const uint32_t raw_start = layer->n_raw - raw_live;
            if (payload_write_bytes(fp,
                                    layer->raw_kv + (uint64_t)raw_start * DS4_N_HEAD_DIM,
                                    (uint64_t)raw_live * DS4_N_HEAD_DIM * sizeof(float),
                                    err,
                                    errlen) != 0) return 1;
            const uint32_t ratio = layer->compress_ratio;
            if (ratio == 0) continue;
            if (payload_write_bytes(fp,
                                    layer->attn_comp_kv,
                                    (uint64_t)layer->n_comp * DS4_N_HEAD_DIM * sizeof(float),
                                    err,
                                    errlen) != 0) return 1;
            if (payload_write_bytes(fp, layer->attn_state_kv, layer_attn_state_bytes(ratio), err, errlen) != 0) return 1;
            if (payload_write_bytes(fp, layer->attn_state_score, layer_attn_state_bytes(ratio), err, errlen) != 0) return 1;
            if (ratio == 4) {
                if (payload_write_bytes(fp,
                                        layer->index_comp_kv,
```

<｜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.c

```c
s->prefill_cap,
            raw_cap,
            raw_cap,
            comp_cap,
            (uint32_t)s->checkpoint.len,
            DS4_N_LAYER,
            DS4_N_HEAD_DIM,
            DS4_N_INDEXER_HEAD_DIM,
            DS4_N_VOCAB,
            raw_live,
        };
        for (uint32_t i = 0; i < DS4_SESSION_PAYLOAD_U32_FIELDS; i++) {
            if (payload_write_u32(fp, header[i], err, errlen) != 0) return 1;
        }
        for (int i = 0; i < s->checkpoint.len; i++) {
            if (payload_write_u32(fp, (uint32_t)s->checkpoint.v[i], err, errlen) != 0) return 1;
        }
        if (payload_write_bytes(fp, s->logits, (uint64_t)DS4_N_VOCAB * sizeof(float), err, errlen) != 0) return 1;
        for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
            if (payload_write_u32(fp, s->cpu_cache.layer[il].n_comp, err, errlen) != 0) return 1;
        }
        for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
            if (payload_write_u32(fp, s->cpu_cache.layer[il].n_index_comp, err, errlen) != 0) return 1;
        }
        for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
            const ds4_layer_cache *layer = &s->cpu_cache.layer[il];
            if (raw_live > layer->n_raw) {
                payload_set_err(err, errlen, "CPU session raw cache has fewer live rows than checkpoint");
                return 1;
            }
            const uint32_t raw_start = layer->n_raw - raw_live;
            if (payload_write_bytes(fp,
                                    layer->raw_kv + (uint64_t)raw_start * DS4_N_HEAD_DIM,
                                    (uint64_t)raw_live * DS4_N_HEAD_DIM * sizeof(float),
                                    err,
                                    errlen) != 0) return 1;
            const uint32_t ratio = layer->compress_ratio;
            if (ratio == 0) continue;
            if (payload_write_bytes(fp,
                                    layer->attn_comp_kv,
                                    (uint64_t)layer->n_comp * DS4_N_HEAD_DIM * sizeof(float),
                                    err,
                                    errlen) != 0) return 1;
            if (payload_write_bytes(fp, layer->attn_state_kv, layer_attn_state_bytes(ratio), err, errlen) != 0) return 1;
            if (payload_write_bytes(fp, layer->attn_state_score, layer_attn_state_bytes(ratio), err, errlen) != 0) return 1;
            if (ratio == 4) {
                if (payload_write_bytes(fp,
                                        layer->index_comp_kv,
```<｜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.c

```c
e_bytes(ratio), err, errlen) != 0) return 1;
            if (ratio == 4) {
                if (payload_write_bytes(fp,
                                        layer->index_comp_kv,
                                        (uint64_t)layer->n_index_comp * DS4_N_INDEXER_HEAD_DIM * sizeof(float),
                                        err,
                                        errlen) != 0) return 1;
                if (payload_write_bytes(fp, layer->index_state_kv, layer_index_state_bytes(ratio), err, errlen) != 0) return 1;
                if (payload_write_bytes(fp, layer->index_state_score, layer_index_state_bytes(ratio), err, errlen) != 0) return 1;
            }
        }
        return 0;
    }
#ifdef DS4_NO_GPU
    payload_set_err(err, errlen, "graph backend support is not compiled in");
    return 1;
#else
    if (ds4_gpu_synchronize() == 0) {
        payload_set_err(err, errlen, "failed to synchronize Metal before snapshot");
        return 1;
    }

    ds4_gpu_graph *g = &s->graph;
    const uint32_t raw_live = session_raw_live_rows(g, (uint32_t)s->checkpoint.len);
    /* Header fields:
     *   0 magic, 1 version, 2 ctx, 3 prefill chunk, 4 raw cap,
     *   5 raw window, 6 compressed cap, 7 token count,
     *   8 layers, 9 raw head dim, 10 indexer head dim, 11 vocab,
     *   12 live raw rows serialized below.
     */
    uint32_t header[DS4_SESSION_PAYLOAD_U32_FIELDS] = {
        DS4_SESSION_PAYLOAD_MAGIC,
        DS4_SESSION_PAYLOAD_VERSION,
        (uint32_t)s->ctx_size,
        s->prefill_cap,
        g->raw_cap,
        g->raw_window,
        g->comp_cap,
        (uint32_t)s->checkpoint.len,
        DS4_N_LAYER,
        DS4_N_HEAD_DIM,
        DS4_N_INDEXER_HEAD_DIM,
        DS4_N_VOCAB,
        raw_live,
    };
    for (uint32_t i = 0; i < DS4_SESSION_PAYLOAD_U32_FIELDS; i++) {
        if (payload_write_u32(fp, header[i], err, errlen) != 0) return 1;
    }
    for (int i = 0; i < s->checkpoint.len; i++) {
        if (payload_write_u32(fp, (uint32_t)s->checkpoint.v[i], err, errlen) != 0) return 1;
    }
    if (payload_write_bytes(fp, s->logits, (uint64_t)DS4_N_VOCAB * sizeof(float), err, errlen) != 0) return 1;
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        if (payload_write_u32(fp, g->layer_n_comp[il], err, errlen) != 0) return 1;
    }
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        if (payload_write_u32(fp, g->layer_n_index_comp[il], err, errlen) != 0) return 1;
    }

    uint8_t *buf = xmalloc(DS4_SESSION_IO_CHUNK);
    int rc = 0;
    for (uint32_t il = 0; rc == 0 && il < DS4_N_LAYER; il++) {
```

<｜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.c

```c
e_bytes(ratio), err, errlen) != 0) return 1;
            if (ratio == 4) {
                if (payload_write_bytes(fp,
                                        layer->index_comp_kv,
                                        (uint64_t)layer->n_index_comp * DS4_N_INDEXER_HEAD_DIM * sizeof(float),
                                        err,
                                        errlen) != 0) return 1;
                if (payload_write_bytes(fp, layer->index_state_kv, layer_index_state_bytes(ratio), err, errlen) != 0) return 1;
                if (payload_write_bytes(fp, layer->index_state_score, layer_index_state_bytes(ratio), err, errlen) != 0) return 1;
            }
        }
        return 0;
    }
#ifdef DS4_NO_GPU
    payload_set_err(err, errlen, "graph backend support is not compiled in");
    return 1;
#else
    if (ds4_gpu_synchronize() == 0) {
        payload_set_err(err, errlen, "failed to synchronize Metal before snapshot");
        return 1;
    }

    ds4_gpu_graph *g = &s->graph;
    const uint32_t raw_live = session_raw_live_rows(g, (uint32_t)s->checkpoint.len);
    /* Header fields:
     *   0 magic, 1 version, 2 ctx, 3 prefill chunk, 4 raw cap,
     *   5 raw window, 6 compressed cap, 7 token count,
     *   8 layers, 9 raw head dim, 10 indexer head dim, 11 vocab,
     *   12 live raw rows serialized below.
     */
    uint32_t header[DS4_SESSION_PAYLOAD_U32_FIELDS] = {
        DS4_SESSION_PAYLOAD_MAGIC,
        DS4_SESSION_PAYLOAD_VERSION,
        (uint32_t)s->ctx_size,
        s->prefill_cap,
        g->raw_cap,
        g->raw_window,
        g->comp_cap,
        (uint32_t)s->checkpoint.len,
        DS4_N_LAYER,
        DS4_N_HEAD_DIM,
        DS4_N_INDEXER_HEAD_DIM,
        DS4_N_VOCAB,
        raw_live,
    };
    for (uint32_t i = 0; i < DS4_SESSION_PAYLOAD_U32_FIELDS; i++) {
        if (payload_write_u32(fp, header[i], err, errlen) != 0) return 1;
    }
    for (int i = 0; i < s->checkpoint.len; i++) {
        if (payload_write_u32(fp, (uint32_t)s->checkpoint.v[i], err, errlen) != 0) return 1;
    }
    if (payload_write_bytes(fp, s->logits, (uint64_t)DS4_N_VOCAB * sizeof(float), err, errlen) != 0) return 1;
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        if (payload_write_u32(fp, g->layer_n_comp[il], err, errlen) != 0) return 1;
    }
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        if (payload_write_u32(fp, g->layer_n_index_comp[il], err, errlen) != 0) return 1;
    }

    uint8_t *buf = xmalloc(DS4_SESSION_IO_CHUNK);
    int rc = 0;
    for (uint32_t il = 0; rc == 0 && il < DS4_N_LAYER; il++) {
```<｜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.c

```c
e_bytes(ratio), err, errlen) != 0) return 1;
            if (ratio == 4) {
                if (payload_write_bytes(fp,
                                        layer->index_comp_kv,
                                        (uint64_t)layer->n_index_comp * DS4_N_INDEXER_HEAD_DIM * sizeof(float),
                                        err,
                                        errlen) != 0) return 1;
                if (payload_write_bytes(fp, layer->index_state_kv, layer_index_state_bytes(ratio), err, errlen) != 0) return 1;
                if (payload_write_bytes(fp, layer->index_state_score, layer_index_state_bytes(ratio), err, errlen) != 0) return 1;
            }
        }
        return 0;
    }
#ifdef DS4_NO_GPU
    payload_set_err(err, errlen, "graph backend support is not compiled in");
    return 1;
#else
    if (ds4_gpu_synchronize() == 0) {
        payload_set_err(err, errlen, "failed to synchronize Metal before snapshot");
        return 1;
    }

    ds4_gpu_graph *g = &s->graph;
    const uint32_t raw_live = session_raw_live_rows(g, (uint32_t)s->checkpoint.len);
    /* Header fields:
     *   0 magic, 1 version, 2 ctx, 3 prefill chunk, 4 raw cap,
     *   5 raw window, 6 compressed cap, 7 token count,
     *   8 layers, 9 raw head dim, 10 indexer head dim, 11 vocab,
     *   12 live raw rows serialized below.
     */
    uint32_t header[DS4_SESSION_PAYLOAD_U32_FIELDS] = {
        DS4_SESSION_PAYLOAD_MAGIC,
        DS4_SESSION_PAYLOAD_VERSION,
        (uint32_t)s->ctx_size,
        s->prefill_cap,
        g->raw_cap,
        g->raw_window,
        g->comp_cap,
        (uint32_t)s->checkpoint.len,
        DS4_N_LAYER,
        DS4_N_HEAD_DIM,
        DS4_N_INDEXER_HEAD_DIM,
        DS4_N_VOCAB,
        raw_live,
    };
    for (uint32_t i = 0; i < DS4_SESSION_PAYLOAD_U32_FIELDS; i++) {
        if (payload_write_u32(fp, header[i], err, errlen) != 0) return 1;
    }
    for (int i = 0; i < s->checkpoint.len; i++) {
        if (payload_write_u32(fp, (uint32_t)s->checkpoint.v[i], err, errlen) != 0) return 1;
    }
    if (payload_write_bytes(fp, s->logits, (uint64_t)DS4_N_VOCAB * sizeof(float), err, errlen) != 0) return 1;
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        if (payload_write_u32(fp, g->layer_n_comp[il], err, errlen) != 0) return 1;
    }
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        if (payload_write_u32(fp, g->layer_n_index_comp[il], err, errlen) != 0) return 1;
    }

    uint8_t *buf = xmalloc(DS4_SESSION_IO_CHUNK);
    int rc = 0;
    for (uint32_t il = 0; rc == 0 && il < DS4_N_LAYER; il++) {
```

<｜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.c

```c
e_bytes(ratio), err, errlen) != 0) return 1;
            if (ratio == 4) {
                if (payload_write_bytes(fp,
                                        layer->index_comp_kv,
                                        (uint64_t)layer->n_index_comp * DS4_N_INDEXER_HEAD_DIM * sizeof(float),
                                        err,
                                        errlen) != 0) return 1;
                if (payload_write_bytes(fp, layer->index_state_kv, layer_index_state_bytes(ratio), err, errlen) != 0) return 1;
                if (payload_write_bytes(fp, layer->index_state_score, layer_index_state_bytes(ratio), err, errlen) != 0) return 1;
            }
        }
        return 0;
    }
#ifdef DS4_NO_GPU
    payload_set_err(err, errlen, "graph backend support is not compiled in");
    return 1;
#else
    if (ds4_gpu_synchronize() == 0) {
        payload_set_err(err, errlen, "failed to synchronize Metal before snapshot");
        return 1;
    }

    ds4_gpu_graph *g = &s->graph;
    const uint32_t raw_live = session_raw_live_rows(g, (uint32_t)s->checkpoint.len);
    /* Header fields:
     *   0 magic, 1 version, 2 ctx, 3 prefill chunk, 4 raw cap,
     *   5 raw window, 6 compressed cap, 7 token count,
     *   8 layers, 9 raw head dim, 10 indexer head dim, 11 vocab,
     *   12 live raw rows serialized below.
     */
    uint32_t header[DS4_SESSION_PAYLOAD_U32_FIELDS] = {
        DS4_SESSION_PAYLOAD_MAGIC,
        DS4_SESSION_PAYLOAD_VERSION,
        (uint32_t)s->ctx_size,
        s->prefill_cap,
        g->raw_cap,
        g->raw_window,
        g->comp_cap,
        (uint32_t)s->checkpoint.len,
        DS4_N_LAYER,
        DS4_N_HEAD_DIM,
        DS4_N_INDEXER_HEAD_DIM,
        DS4_N_VOCAB,
        raw_live,
    };
    for (uint32_t i = 0; i < DS4_SESSION_PAYLOAD_U32_FIELDS; i++) {
        if (payload_write_u32(fp, header[i], err, errlen) != 0) return 1;
    }
    for (int i = 0; i < s->checkpoint.len; i++) {
        if (payload_write_u32(fp, (uint32_t)s->checkpoint.v[i], err, errlen) != 0) return 1;
    }
    if (payload_write_bytes(fp, s->logits, (uint64_t)DS4_N_VOCAB * sizeof(float), err, errlen) != 0) return 1;
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        if (payload_write_u32(fp, g->layer_n_comp[il], err, errlen) != 0) return 1;
    }
    for (uint32_t il = 0; il < DS4_N_LAYER; il++) {
        if (payload_write_u32(fp, g->layer_n_index_comp[il], err, errlen) != 0) return 1;
    }

    uint8_t *buf = xmalloc(DS4_SESSION_IO_CHUNK);
    int rc = 0;
    for (uint32_t il = 0; rc == 0 && il < DS4_N_LAYER; il++) {
```<｜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.c

```c
index_comp[il], err, errlen) != 0) return 1;
    }

    uint8_t *buf = xmalloc(DS4_SESSION_IO_CHUNK);
    int rc = 0;
    for (uint32_t il = 0; rc == 0 && il < DS4_N_LAYER; il++) {
        /* Write the raw ring in logical position order.  The file does not care
         * where the rows happened to live physically in the source graph. */
        const uint32_t raw_first = (uint32_t)s->checkpoint.len - raw_live;
        for (uint32_t r = 0; rc == 0 && r < raw_live; r++) {
            const uint32_t pos = raw_first + r;
            const uint32_t phys = pos % g->raw_cap;
            rc = payload_write_tensor_span(fp,
                                           g->layer_raw_cache[il],
                                           (uint64_t)phys * DS4_N_HEAD_DIM * sizeof(float),
                                           (uint64_t)DS4_N_HEAD_DIM * sizeof(float),
                                           buf,
                                           DS4_SESSION_IO_CHUNK,
                                           err,
                                           errlen);
        }
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (rc != 0 || ratio == 0) continue;
        /* Compressed rows are append-only from row zero, so the live prefix is
         * contiguous.  The two compressor state tensors hold the partial window
         * that will become the next compressed row. */
        rc = payload_write_tensor_span(fp,
                                       g->layer_attn_comp_cache[il],
                                       0,
                                       (uint64_t)g->layer_n_comp[il] * DS4_N_HEAD_DIM * sizeof(float),
                                       buf,
                                       DS4_SESSION_IO_CHUNK,
                                       err,
                                       errlen);
        if (rc == 0) rc = payload_write_tensor_span(fp,
                                                    g->layer_attn_state_kv[il],
                                                    0,
                                                    layer_attn_state_bytes(ratio),
                                                    buf,
                                                    DS4_SESSION_IO_CHUNK,
                                                    err,
                                                    errlen);
        if (rc == 0) rc = payload_write_tensor_span(fp,
                                                    g->layer_attn_state_score[il],
                                                    0,
```

<｜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.c

```c
index_comp[il], err, errlen) != 0) return 1;
    }

    uint8_t *buf = xmalloc(DS4_SESSION_IO_CHUNK);
    int rc = 0;
    for (uint32_t il = 0; rc == 0 && il < DS4_N_LAYER; il++) {
        /* Write the raw ring in logical position order.  The file does not care
         * where the rows happened to live physically in the source graph. */
        const uint32_t raw_first = (uint32_t)s->checkpoint.len - raw_live;
        for (uint32_t r = 0; rc == 0 && r < raw_live; r++) {
            const uint32_t pos = raw_first + r;
            const uint32_t phys = pos % g->raw_cap;
            rc = payload_write_tensor_span(fp,
                                           g->layer_raw_cache[il],
                                           (uint64_t)phys * DS4_N_HEAD_DIM * sizeof(float),
                                           (uint64_t)DS4_N_HEAD_DIM * sizeof(float),
                                           buf,
                                           DS4_SESSION_IO_CHUNK,
                                           err,
                                           errlen);
        }
        const uint32_t ratio = ds4_layer_compress_ratio(il);
        if (rc != 0 || ratio == 0) continue;
        /* Compressed rows are append-only from row zero, so the live prefix is
         * contiguous.  The two compressor state tensors hold the partial window
         * that will become the next compressed row. */
        rc = payload_write_tensor_span(fp,
                                       g->layer_attn_comp_cache[il],
                                       0,
                                       (uint64_t)g->layer_n_comp[il] * DS4_N_HEAD_DIM * sizeof(float),
                                       buf,
                                       DS4_SESSION_IO_CHUNK,
                                       err,
                                       errlen);
        if (rc == 0) rc = payload_write_tensor_span(fp,
                                                    g->layer_attn_state_kv[il],
                                                    0,
                                                    layer_attn_state_bytes(ratio),
                                                    buf,
                                                    DS4_SESSION_IO_CHUNK,
                                                    err,
                                                    errlen);
        if (rc == 0) rc = payload_write_tensor_span(fp,
                                                    g->layer_attn_state_score[il],
                                                    0,
```<｜Assistant｜></think>