static int DecodeImageStream()

in Extended/libwebp/src/dec/vp8l_dec.c [1414:1501]
73 lines of code
18 McCabe index (conditional complexity)

static int DecodeImageStream(int xsize, int ysize,
                             int is_level0,
                             VP8LDecoder* const dec,
                             uint32_t** const decoded_data) {
  int ok = 1;
  int transform_xsize = xsize;
  int transform_ysize = ysize;
  VP8LBitReader* const br = &dec->br_;
  VP8LMetadata* const hdr = &dec->hdr_;
  uint32_t* data = NULL;
  int color_cache_bits = 0;

  // Read the transforms (may recurse).
  if (is_level0) {
    while (ok && VP8LReadBits(br, 1)) {
      ok = ReadTransform(&transform_xsize, &transform_ysize, dec);
    }
  }

  // Color cache
  if (ok && VP8LReadBits(br, 1)) {
    color_cache_bits = VP8LReadBits(br, 4);
    ok = (color_cache_bits >= 1 && color_cache_bits <= MAX_CACHE_BITS);
    if (!ok) {
      dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
      goto End;
    }
  }

  // Read the Huffman codes (may recurse).
  ok = ok && ReadHuffmanCodes(dec, transform_xsize, transform_ysize,
                              color_cache_bits, is_level0);
  if (!ok) {
    dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
    goto End;
  }

  // Finish setting up the color-cache
  if (color_cache_bits > 0) {
    hdr->color_cache_size_ = 1 << color_cache_bits;
    if (!VP8LColorCacheInit(&hdr->color_cache_, color_cache_bits)) {
      dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
      ok = 0;
      goto End;
    }
  } else {
    hdr->color_cache_size_ = 0;
  }
  UpdateDecoder(dec, transform_xsize, transform_ysize);

  if (is_level0) {   // level 0 complete
    dec->state_ = READ_HDR;
    goto End;
  }

  {
    const uint64_t total_size = (uint64_t)transform_xsize * transform_ysize;
    data = (uint32_t*)WebPSafeMalloc(total_size, sizeof(*data));
    if (data == NULL) {
      dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
      ok = 0;
      goto End;
    }
  }

  // Use the Huffman trees to decode the LZ77 encoded data.
  ok = DecodeImageData(dec, data, transform_xsize, transform_ysize,
                       transform_ysize, NULL);
  ok = ok && !br->eos_;

 End:
  if (!ok) {
    WebPSafeFree(data);
    ClearMetadata(hdr);
  } else {
    if (decoded_data != NULL) {
      *decoded_data = data;
    } else {
      // We allocate image data in this function only for transforms. At level 0
      // (that is: not the transforms), we shouldn't have allocated anything.
      assert(data == NULL);
      assert(is_level0);
    }
    dec->last_pixel_ = 0;  // Reset for future DECODE_DATA_FUNC() calls.
    if (!is_level0) ClearMetadata(hdr);  // Clean up temporary data behind.
  }
  return ok;
}