static void ReconstructRow()

in Extended/libwebp/src/dec/frame_dec.c [71:191]
98 lines of code
18 McCabe index (conditional complexity)

static void ReconstructRow(const VP8Decoder* const dec,
                           const VP8ThreadContext* ctx) {
  int j;
  int mb_x;
  const int mb_y = ctx->mb_y_;
  const int cache_id = ctx->id_;
  uint8_t* const y_dst = dec->yuv_b_ + Y_OFF;
  uint8_t* const u_dst = dec->yuv_b_ + U_OFF;
  uint8_t* const v_dst = dec->yuv_b_ + V_OFF;

  // Initialize left-most block.
  for (j = 0; j < 16; ++j) {
    y_dst[j * BPS - 1] = 129;
  }
  for (j = 0; j < 8; ++j) {
    u_dst[j * BPS - 1] = 129;
    v_dst[j * BPS - 1] = 129;
  }

  // Init top-left sample on left column too.
  if (mb_y > 0) {
    y_dst[-1 - BPS] = u_dst[-1 - BPS] = v_dst[-1 - BPS] = 129;
  } else {
    // we only need to do this init once at block (0,0).
    // Afterward, it remains valid for the whole topmost row.
    memset(y_dst - BPS - 1, 127, 16 + 4 + 1);
    memset(u_dst - BPS - 1, 127, 8 + 1);
    memset(v_dst - BPS - 1, 127, 8 + 1);
  }

  // Reconstruct one row.
  for (mb_x = 0; mb_x < dec->mb_w_; ++mb_x) {
    const VP8MBData* const block = ctx->mb_data_ + mb_x;

    // Rotate in the left samples from previously decoded block. We move four
    // pixels at a time for alignment reason, and because of in-loop filter.
    if (mb_x > 0) {
      for (j = -1; j < 16; ++j) {
        Copy32b(&y_dst[j * BPS - 4], &y_dst[j * BPS + 12]);
      }
      for (j = -1; j < 8; ++j) {
        Copy32b(&u_dst[j * BPS - 4], &u_dst[j * BPS + 4]);
        Copy32b(&v_dst[j * BPS - 4], &v_dst[j * BPS + 4]);
      }
    }
    {
      // bring top samples into the cache
      VP8TopSamples* const top_yuv = dec->yuv_t_ + mb_x;
      const int16_t* const coeffs = block->coeffs_;
      uint32_t bits = block->non_zero_y_;
      int n;

      if (mb_y > 0) {
        memcpy(y_dst - BPS, top_yuv[0].y, 16);
        memcpy(u_dst - BPS, top_yuv[0].u, 8);
        memcpy(v_dst - BPS, top_yuv[0].v, 8);
      }

      // predict and add residuals
      if (block->is_i4x4_) {   // 4x4
        uint32_t* const top_right = (uint32_t*)(y_dst - BPS + 16);

        if (mb_y > 0) {
          if (mb_x >= dec->mb_w_ - 1) {    // on rightmost border
            memset(top_right, top_yuv[0].y[15], sizeof(*top_right));
          } else {
            memcpy(top_right, top_yuv[1].y, sizeof(*top_right));
          }
        }
        // replicate the top-right pixels below
        top_right[BPS] = top_right[2 * BPS] = top_right[3 * BPS] = top_right[0];

        // predict and add residuals for all 4x4 blocks in turn.
        for (n = 0; n < 16; ++n, bits <<= 2) {
          uint8_t* const dst = y_dst + kScan[n];
          VP8PredLuma4[block->imodes_[n]](dst);
          DoTransform(bits, coeffs + n * 16, dst);
        }
      } else {    // 16x16
        const int pred_func = CheckMode(mb_x, mb_y, block->imodes_[0]);
        VP8PredLuma16[pred_func](y_dst);
        if (bits != 0) {
          for (n = 0; n < 16; ++n, bits <<= 2) {
            DoTransform(bits, coeffs + n * 16, y_dst + kScan[n]);
          }
        }
      }
      {
        // Chroma
        const uint32_t bits_uv = block->non_zero_uv_;
        const int pred_func = CheckMode(mb_x, mb_y, block->uvmode_);
        VP8PredChroma8[pred_func](u_dst);
        VP8PredChroma8[pred_func](v_dst);
        DoUVTransform(bits_uv >> 0, coeffs + 16 * 16, u_dst);
        DoUVTransform(bits_uv >> 8, coeffs + 20 * 16, v_dst);
      }

      // stash away top samples for next block
      if (mb_y < dec->mb_h_ - 1) {
        memcpy(top_yuv[0].y, y_dst + 15 * BPS, 16);
        memcpy(top_yuv[0].u, u_dst +  7 * BPS,  8);
        memcpy(top_yuv[0].v, v_dst +  7 * BPS,  8);
      }
    }
    // Transfer reconstructed samples from yuv_b_ cache to final destination.
    {
      const int y_offset = cache_id * 16 * dec->cache_y_stride_;
      const int uv_offset = cache_id * 8 * dec->cache_uv_stride_;
      uint8_t* const y_out = dec->cache_y_ + mb_x * 16 + y_offset;
      uint8_t* const u_out = dec->cache_u_ + mb_x * 8 + uv_offset;
      uint8_t* const v_out = dec->cache_v_ + mb_x * 8 + uv_offset;
      for (j = 0; j < 16; ++j) {
        memcpy(y_out + j * dec->cache_y_stride_, y_dst + j * BPS, 16);
      }
      for (j = 0; j < 8; ++j) {
        memcpy(u_out + j * dec->cache_uv_stride_, u_dst + j * BPS, 8);
        memcpy(v_out + j * dec->cache_uv_stride_, v_dst + j * BPS, 8);
      }
    }
  }
}