static int FinishRow()

in Extended/libwebp/src/dec/frame_dec.c [402:495]
86 lines of code
17 McCabe index (conditional complexity)

static int FinishRow(void* arg1, void* arg2) {
  VP8Decoder* const dec = (VP8Decoder*)arg1;
  VP8Io* const io = (VP8Io*)arg2;
  int ok = 1;
  const VP8ThreadContext* const ctx = &dec->thread_ctx_;
  const int cache_id = ctx->id_;
  const int extra_y_rows = kFilterExtraRows[dec->filter_type_];
  const int ysize = extra_y_rows * dec->cache_y_stride_;
  const int uvsize = (extra_y_rows / 2) * dec->cache_uv_stride_;
  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 ydst = dec->cache_y_ - ysize + y_offset;
  uint8_t* const udst = dec->cache_u_ - uvsize + uv_offset;
  uint8_t* const vdst = dec->cache_v_ - uvsize + uv_offset;
  const int mb_y = ctx->mb_y_;
  const int is_first_row = (mb_y == 0);
  const int is_last_row = (mb_y >= dec->br_mb_y_ - 1);

  if (dec->mt_method_ == 2) {
    ReconstructRow(dec, ctx);
  }

  if (ctx->filter_row_) {
    FilterRow(dec);
  }

  if (dec->dither_) {
    DitherRow(dec);
  }

  if (io->put != NULL) {
    int y_start = MACROBLOCK_VPOS(mb_y);
    int y_end = MACROBLOCK_VPOS(mb_y + 1);
    if (!is_first_row) {
      y_start -= extra_y_rows;
      io->y = ydst;
      io->u = udst;
      io->v = vdst;
    } else {
      io->y = dec->cache_y_ + y_offset;
      io->u = dec->cache_u_ + uv_offset;
      io->v = dec->cache_v_ + uv_offset;
    }

    if (!is_last_row) {
      y_end -= extra_y_rows;
    }
    if (y_end > io->crop_bottom) {
      y_end = io->crop_bottom;    // make sure we don't overflow on last row.
    }
    // If dec->alpha_data_ is not NULL, we have some alpha plane present.
    io->a = NULL;
    if (dec->alpha_data_ != NULL && y_start < y_end) {
      io->a = VP8DecompressAlphaRows(dec, io, y_start, y_end - y_start);
      if (io->a == NULL) {
        return VP8SetError(dec, VP8_STATUS_BITSTREAM_ERROR,
                           "Could not decode alpha data.");
      }
    }
    if (y_start < io->crop_top) {
      const int delta_y = io->crop_top - y_start;
      y_start = io->crop_top;
      assert(!(delta_y & 1));
      io->y += dec->cache_y_stride_ * delta_y;
      io->u += dec->cache_uv_stride_ * (delta_y >> 1);
      io->v += dec->cache_uv_stride_ * (delta_y >> 1);
      if (io->a != NULL) {
        io->a += io->width * delta_y;
      }
    }
    if (y_start < y_end) {
      io->y += io->crop_left;
      io->u += io->crop_left >> 1;
      io->v += io->crop_left >> 1;
      if (io->a != NULL) {
        io->a += io->crop_left;
      }
      io->mb_y = y_start - io->crop_top;
      io->mb_w = io->crop_right - io->crop_left;
      io->mb_h = y_end - y_start;
      ok = io->put(io);
    }
  }
  // rotate top samples if needed
  if (cache_id + 1 == dec->num_caches_) {
    if (!is_last_row) {
      memcpy(dec->cache_y_ - ysize, ydst + 16 * dec->cache_y_stride_, ysize);
      memcpy(dec->cache_u_ - uvsize, udst + 8 * dec->cache_uv_stride_, uvsize);
      memcpy(dec->cache_v_ - uvsize, vdst + 8 * dec->cache_uv_stride_, uvsize);
    }
  }

  return ok;
}