Use the upstream version of libwebp, v0.4.3.

third_party/libwebp/dec/vp8l.c

+// Copyright 2012 Google Inc. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+// -----------------------------------------------------------------------------
+//
+// main entry for the decoder
+//
+// Authors: Vikas Arora (vikaas.arora@gmail.com)
+//          Jyrki Alakuijala (jyrki@google.com)
+
+#include <stdlib.h>
+
+#include "./alphai.h"
+#include "./vp8li.h"
+#include "../dsp/dsp.h"
+#include "../dsp/lossless.h"
+#include "../dsp/yuv.h"
+#include "../utils/huffman.h"
+#include "../utils/utils.h"
+
+#define NUM_ARGB_CACHE_ROWS          16
+
+static const int kCodeLengthLiterals = 16;
+static const int kCodeLengthRepeatCode = 16;
+static const int kCodeLengthExtraBits[3] = { 2, 3, 7 };
+static const int kCodeLengthRepeatOffsets[3] = { 3, 3, 11 };
+
+// -----------------------------------------------------------------------------
+//  Five Huffman codes are used at each meta code:
+//  1. green + length prefix codes + color cache codes,
+//  2. alpha,
+//  3. red,
+//  4. blue, and,
+//  5. distance prefix codes.
+typedef enum {
+  GREEN = 0,
+  RED   = 1,
+  BLUE  = 2,
+  ALPHA = 3,
+  DIST  = 4
+} HuffIndex;
+
+static const uint16_t kAlphabetSize[HUFFMAN_CODES_PER_META_CODE] = {
+  NUM_LITERAL_CODES + NUM_LENGTH_CODES,
+  NUM_LITERAL_CODES, NUM_LITERAL_CODES, NUM_LITERAL_CODES,
+  NUM_DISTANCE_CODES
+};
+
+
+#define NUM_CODE_LENGTH_CODES       19
+static const uint8_t kCodeLengthCodeOrder[NUM_CODE_LENGTH_CODES] = {
+  17, 18, 0, 1, 2, 3, 4, 5, 16, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15
+};
+
+#define CODE_TO_PLANE_CODES        120
+static const uint8_t kCodeToPlane[CODE_TO_PLANE_CODES] = {
+  0x18, 0x07, 0x17, 0x19, 0x28, 0x06, 0x27, 0x29, 0x16, 0x1a,
+  0x26, 0x2a, 0x38, 0x05, 0x37, 0x39, 0x15, 0x1b, 0x36, 0x3a,
+  0x25, 0x2b, 0x48, 0x04, 0x47, 0x49, 0x14, 0x1c, 0x35, 0x3b,
+  0x46, 0x4a, 0x24, 0x2c, 0x58, 0x45, 0x4b, 0x34, 0x3c, 0x03,
+  0x57, 0x59, 0x13, 0x1d, 0x56, 0x5a, 0x23, 0x2d, 0x44, 0x4c,
+  0x55, 0x5b, 0x33, 0x3d, 0x68, 0x02, 0x67, 0x69, 0x12, 0x1e,
+  0x66, 0x6a, 0x22, 0x2e, 0x54, 0x5c, 0x43, 0x4d, 0x65, 0x6b,
+  0x32, 0x3e, 0x78, 0x01, 0x77, 0x79, 0x53, 0x5d, 0x11, 0x1f,
+  0x64, 0x6c, 0x42, 0x4e, 0x76, 0x7a, 0x21, 0x2f, 0x75, 0x7b,
+  0x31, 0x3f, 0x63, 0x6d, 0x52, 0x5e, 0x00, 0x74, 0x7c, 0x41,
+  0x4f, 0x10, 0x20, 0x62, 0x6e, 0x30, 0x73, 0x7d, 0x51, 0x5f,
+  0x40, 0x72, 0x7e, 0x61, 0x6f, 0x50, 0x71, 0x7f, 0x60, 0x70
+};
+
+static int DecodeImageStream(int xsize, int ysize,
+                             int is_level0,
+                             VP8LDecoder* const dec,
+                             uint32_t** const decoded_data);
+
+//------------------------------------------------------------------------------
+
+int VP8LCheckSignature(const uint8_t* const data, size_t size) {
+  return (size >= VP8L_FRAME_HEADER_SIZE &&
+          data[0] == VP8L_MAGIC_BYTE &&
+          (data[4] >> 5) == 0);  // version
+}
+
+static int ReadImageInfo(VP8LBitReader* const br,
+                         int* const width, int* const height,
+                         int* const has_alpha) {
+  if (VP8LReadBits(br, 8) != VP8L_MAGIC_BYTE) return 0;
+  *width = VP8LReadBits(br, VP8L_IMAGE_SIZE_BITS) + 1;
+  *height = VP8LReadBits(br, VP8L_IMAGE_SIZE_BITS) + 1;
+  *has_alpha = VP8LReadBits(br, 1);
+  if (VP8LReadBits(br, VP8L_VERSION_BITS) != 0) return 0;
+  return 1;
+}
+
+int VP8LGetInfo(const uint8_t* data, size_t data_size,
+                int* const width, int* const height, int* const has_alpha) {
+  if (data == NULL || data_size < VP8L_FRAME_HEADER_SIZE) {
+    return 0;         // not enough data
+  } else if (!VP8LCheckSignature(data, data_size)) {
+    return 0;         // bad signature
+  } else {
+    int w, h, a;
+    VP8LBitReader br;
+    VP8LInitBitReader(&br, data, data_size);
+    if (!ReadImageInfo(&br, &w, &h, &a)) {
+      return 0;
+    }
+    if (width != NULL) *width = w;
+    if (height != NULL) *height = h;
+    if (has_alpha != NULL) *has_alpha = a;
+    return 1;
+  }
+}
+
+//------------------------------------------------------------------------------
+
+static WEBP_INLINE int GetCopyDistance(int distance_symbol,
+                                       VP8LBitReader* const br) {
+  int extra_bits, offset;
+  if (distance_symbol < 4) {
+    return distance_symbol + 1;
+  }
+  extra_bits = (distance_symbol - 2) >> 1;
+  offset = (2 + (distance_symbol & 1)) << extra_bits;
+  return offset + VP8LReadBits(br, extra_bits) + 1;
+}
+
+static WEBP_INLINE int GetCopyLength(int length_symbol,
+                                     VP8LBitReader* const br) {
+  // Length and distance prefixes are encoded the same way.
+  return GetCopyDistance(length_symbol, br);
+}
+
+static WEBP_INLINE int PlaneCodeToDistance(int xsize, int plane_code) {
+  if (plane_code > CODE_TO_PLANE_CODES) {
+    return plane_code - CODE_TO_PLANE_CODES;
+  } else {
+    const int dist_code = kCodeToPlane[plane_code - 1];
+    const int yoffset = dist_code >> 4;
+    const int xoffset = 8 - (dist_code & 0xf);
+    const int dist = yoffset * xsize + xoffset;
+    return (dist >= 1) ? dist : 1;  // dist<1 can happen if xsize is very small
+  }
+}
+
+//------------------------------------------------------------------------------
+// Decodes the next Huffman code from bit-stream.
+// FillBitWindow(br) needs to be called at minimum every second call
+// to ReadSymbol, in order to pre-fetch enough bits.
+static WEBP_INLINE int ReadSymbol(const HuffmanTree* tree,
+                                  VP8LBitReader* const br) {
+  const HuffmanTreeNode* node = tree->root_;
+  uint32_t bits = VP8LPrefetchBits(br);
+  int bitpos = br->bit_pos_;
+  // Check if we find the bit combination from the Huffman lookup table.
+  const int lut_ix = bits & (HUFF_LUT - 1);
+  const int lut_bits = tree->lut_bits_[lut_ix];
+  if (lut_bits <= HUFF_LUT_BITS) {
+    VP8LSetBitPos(br, bitpos + lut_bits);
+    return tree->lut_symbol_[lut_ix];
+  }
+  node += tree->lut_jump_[lut_ix];
+  bitpos += HUFF_LUT_BITS;
+  bits >>= HUFF_LUT_BITS;
+
+  // Decode the value from a binary tree.
+  assert(node != NULL);
+  do {
+    node = HuffmanTreeNextNode(node, bits & 1);
+    bits >>= 1;
+    ++bitpos;
+  } while (HuffmanTreeNodeIsNotLeaf(node));
+  VP8LSetBitPos(br, bitpos);
+  return node->symbol_;
+}
+
+static int ReadHuffmanCodeLengths(
+    VP8LDecoder* const dec, const int* const code_length_code_lengths,
+    int num_symbols, int* const code_lengths) {
+  int ok = 0;
+  VP8LBitReader* const br = &dec->br_;
+  int symbol;
+  int max_symbol;
+  int prev_code_len = DEFAULT_CODE_LENGTH;
+  HuffmanTree tree;
+  int huff_codes[NUM_CODE_LENGTH_CODES] = { 0 };
+
+  if (!VP8LHuffmanTreeBuildImplicit(&tree, code_length_code_lengths,
+                                    huff_codes, NUM_CODE_LENGTH_CODES)) {
+    dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
+    return 0;
+  }
+
+  if (VP8LReadBits(br, 1)) {    // use length
+    const int length_nbits = 2 + 2 * VP8LReadBits(br, 3);
+    max_symbol = 2 + VP8LReadBits(br, length_nbits);
+    if (max_symbol > num_symbols) {
+      dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
+      goto End;
+    }
+  } else {
+    max_symbol = num_symbols;
+  }
+
+  symbol = 0;
+  while (symbol < num_symbols) {
+    int code_len;
+    if (max_symbol-- == 0) break;
+    VP8LFillBitWindow(br);
+    code_len = ReadSymbol(&tree, br);
+    if (code_len < kCodeLengthLiterals) {
+      code_lengths[symbol++] = code_len;
+      if (code_len != 0) prev_code_len = code_len;
+    } else {
+      const int use_prev = (code_len == kCodeLengthRepeatCode);
+      const int slot = code_len - kCodeLengthLiterals;
+      const int extra_bits = kCodeLengthExtraBits[slot];
+      const int repeat_offset = kCodeLengthRepeatOffsets[slot];
+      int repeat = VP8LReadBits(br, extra_bits) + repeat_offset;
+      if (symbol + repeat > num_symbols) {
+        dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
+        goto End;
+      } else {
+        const int length = use_prev ? prev_code_len : 0;
+        while (repeat-- > 0) code_lengths[symbol++] = length;
+      }
+    }
+  }
+  ok = 1;
+
+ End:
+  VP8LHuffmanTreeFree(&tree);
+  if (!ok) dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
+  return ok;
+}
+
+// 'code_lengths' is pre-allocated temporary buffer, used for creating Huffman
+// tree.
+static int ReadHuffmanCode(int alphabet_size, VP8LDecoder* const dec,
+                           int* const code_lengths, int* const huff_codes,
+                           HuffmanTree* const tree) {
+  int ok = 0;
+  VP8LBitReader* const br = &dec->br_;
+  const int simple_code = VP8LReadBits(br, 1);
+
+  if (simple_code) {  // Read symbols, codes & code lengths directly.
+    int symbols[2];
+    int codes[2];
+    const int num_symbols = VP8LReadBits(br, 1) + 1;
+    const int first_symbol_len_code = VP8LReadBits(br, 1);
+    // The first code is either 1 bit or 8 bit code.
+    symbols[0] = VP8LReadBits(br, (first_symbol_len_code == 0) ? 1 : 8);
+    codes[0] = 0;
+    code_lengths[0] = num_symbols - 1;
+    // The second code (if present), is always 8 bit long.
+    if (num_symbols == 2) {
+      symbols[1] = VP8LReadBits(br, 8);
+      codes[1] = 1;
+      code_lengths[1] = num_symbols - 1;
+    }
+    ok = VP8LHuffmanTreeBuildExplicit(tree, code_lengths, codes, symbols,
+                                      alphabet_size, num_symbols);
+  } else {  // Decode Huffman-coded code lengths.
+    int i;
+    int code_length_code_lengths[NUM_CODE_LENGTH_CODES] = { 0 };
+    const int num_codes = VP8LReadBits(br, 4) + 4;
+    if (num_codes > NUM_CODE_LENGTH_CODES) {
+      dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
+      return 0;
+    }
+
+    memset(code_lengths, 0, alphabet_size * sizeof(*code_lengths));
+
+    for (i = 0; i < num_codes; ++i) {
+      code_length_code_lengths[kCodeLengthCodeOrder[i]] = VP8LReadBits(br, 3);
+    }
+    ok = ReadHuffmanCodeLengths(dec, code_length_code_lengths, alphabet_size,
+                                code_lengths);
+    ok = ok && VP8LHuffmanTreeBuildImplicit(tree, code_lengths, huff_codes,
+                                            alphabet_size);
+  }
+  ok = ok && !br->error_;
+  if (!ok) {
+    dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
+    return 0;
+  }
+  return 1;
+}
+
+static int ReadHuffmanCodes(VP8LDecoder* const dec, int xsize, int ysize,
+                            int color_cache_bits, int allow_recursion) {
+  int i, j;
+  VP8LBitReader* const br = &dec->br_;
+  VP8LMetadata* const hdr = &dec->hdr_;
+  uint32_t* huffman_image = NULL;
+  HTreeGroup* htree_groups = NULL;
+  int num_htree_groups = 1;
+  int max_alphabet_size = 0;
+  int* code_lengths = NULL;
+  int* huff_codes = NULL;
+
+  if (allow_recursion && VP8LReadBits(br, 1)) {
+    // use meta Huffman codes.
+    const int huffman_precision = VP8LReadBits(br, 3) + 2;
+    const int huffman_xsize = VP8LSubSampleSize(xsize, huffman_precision);
+    const int huffman_ysize = VP8LSubSampleSize(ysize, huffman_precision);
+    const int huffman_pixs = huffman_xsize * huffman_ysize;
+    if (!DecodeImageStream(huffman_xsize, huffman_ysize, 0, dec,
+                           &huffman_image)) {
+      dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
+      goto Error;
+    }
+    hdr->huffman_subsample_bits_ = huffman_precision;
+    for (i = 0; i < huffman_pixs; ++i) {
+      // The huffman data is stored in red and green bytes.
+      const int group = (huffman_image[i] >> 8) & 0xffff;
+      huffman_image[i] = group;
+      if (group >= num_htree_groups) {
+        num_htree_groups = group + 1;
+      }
+    }
+  }
+
+  if (br->error_) goto Error;
+
+  // Find maximum alphabet size for the htree group.
+  for (j = 0; j < HUFFMAN_CODES_PER_META_CODE; ++j) {
+    int alphabet_size = kAlphabetSize[j];
+    if (j == 0 && color_cache_bits > 0) {
+      alphabet_size += 1 << color_cache_bits;
+    }
+    if (max_alphabet_size < alphabet_size) {
+      max_alphabet_size = alphabet_size;
+    }
+  }
+
+  htree_groups = VP8LHtreeGroupsNew(num_htree_groups);
+  code_lengths =
+      (int*)WebPSafeCalloc((uint64_t)max_alphabet_size, sizeof(*code_lengths));
+  huff_codes =
+      (int*)WebPSafeMalloc((uint64_t)max_alphabet_size, sizeof(*huff_codes));
+
+  if (htree_groups == NULL || code_lengths == NULL || huff_codes == NULL) {
+    dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
+    goto Error;
+  }
+
+  for (i = 0; i < num_htree_groups; ++i) {
+    HuffmanTree* const htrees = htree_groups[i].htrees_;
+    for (j = 0; j < HUFFMAN_CODES_PER_META_CODE; ++j) {
+      int alphabet_size = kAlphabetSize[j];
+      HuffmanTree* const htree = htrees + j;
+      if (j == 0 && color_cache_bits > 0) {
+        alphabet_size += 1 << color_cache_bits;
+      }
+      if (!ReadHuffmanCode(alphabet_size, dec, code_lengths, huff_codes,
+                           htree)) {
+        goto Error;
+      }
+    }
+  }
+  WebPSafeFree(huff_codes);
+  WebPSafeFree(code_lengths);
+
+  // All OK. Finalize pointers and return.
+  hdr->huffman_image_ = huffman_image;
+  hdr->num_htree_groups_ = num_htree_groups;
+  hdr->htree_groups_ = htree_groups;
+  return 1;
+
+ Error:
+  WebPSafeFree(huff_codes);
+  WebPSafeFree(code_lengths);
+  WebPSafeFree(huffman_image);
+  VP8LHtreeGroupsFree(htree_groups, num_htree_groups);
+  return 0;
+}
+
+//------------------------------------------------------------------------------
+// Scaling.
+
+static int AllocateAndInitRescaler(VP8LDecoder* const dec, VP8Io* const io) {
+  const int num_channels = 4;
+  const int in_width = io->mb_w;
+  const int out_width = io->scaled_width;
+  const int in_height = io->mb_h;
+  const int out_height = io->scaled_height;
+  const uint64_t work_size = 2 * num_channels * (uint64_t)out_width;
+  int32_t* work;        // Rescaler work area.
+  const uint64_t scaled_data_size = num_channels * (uint64_t)out_width;
+  uint32_t* scaled_data;  // Temporary storage for scaled BGRA data.
+  const uint64_t memory_size = sizeof(*dec->rescaler) +
+                               work_size * sizeof(*work) +
+                               scaled_data_size * sizeof(*scaled_data);
+  uint8_t* memory = (uint8_t*)WebPSafeCalloc(memory_size, sizeof(*memory));
+  if (memory == NULL) {
+    dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
+    return 0;
+  }
+  assert(dec->rescaler_memory == NULL);
+  dec->rescaler_memory = memory;
+
+  dec->rescaler = (WebPRescaler*)memory;
+  memory += sizeof(*dec->rescaler);
+  work = (int32_t*)memory;
+  memory += work_size * sizeof(*work);
+  scaled_data = (uint32_t*)memory;
+
+  WebPRescalerInit(dec->rescaler, in_width, in_height, (uint8_t*)scaled_data,
+                   out_width, out_height, 0, num_channels,
+                   in_width, out_width, in_height, out_height, work);
+  return 1;
+}
+
+//------------------------------------------------------------------------------
+// Export to ARGB
+
+// We have special "export" function since we need to convert from BGRA
+static int Export(WebPRescaler* const rescaler, WEBP_CSP_MODE colorspace,
+                  int rgba_stride, uint8_t* const rgba) {
+  uint32_t* const src = (uint32_t*)rescaler->dst;
+  const int dst_width = rescaler->dst_width;
+  int num_lines_out = 0;
+  while (WebPRescalerHasPendingOutput(rescaler)) {
+    uint8_t* const dst = rgba + num_lines_out * rgba_stride;
+    WebPRescalerExportRow(rescaler, 0);
+    WebPMultARGBRow(src, dst_width, 1);
+    VP8LConvertFromBGRA(src, dst_width, colorspace, dst);
+    ++num_lines_out;
+  }
+  return num_lines_out;
+}
+
+// Emit scaled rows.
+static int EmitRescaledRowsRGBA(const VP8LDecoder* const dec,
+                                uint8_t* in, int in_stride, int mb_h,
+                                uint8_t* const out, int out_stride) {
+  const WEBP_CSP_MODE colorspace = dec->output_->colorspace;
+  int num_lines_in = 0;
+  int num_lines_out = 0;
+  while (num_lines_in < mb_h) {
+    uint8_t* const row_in = in + num_lines_in * in_stride;
+    uint8_t* const row_out = out + num_lines_out * out_stride;
+    const int lines_left = mb_h - num_lines_in;
+    const int needed_lines = WebPRescaleNeededLines(dec->rescaler, lines_left);
+    assert(needed_lines > 0 && needed_lines <= lines_left);
+    WebPMultARGBRows(row_in, in_stride,
+                     dec->rescaler->src_width, needed_lines, 0);
+    WebPRescalerImport(dec->rescaler, lines_left, row_in, in_stride);
+    num_lines_in += needed_lines;
+    num_lines_out += Export(dec->rescaler, colorspace, out_stride, row_out);
+  }
+  return num_lines_out;
+}
+
+// Emit rows without any scaling.
+static int EmitRows(WEBP_CSP_MODE colorspace,
+                    const uint8_t* row_in, int in_stride,
+                    int mb_w, int mb_h,
+                    uint8_t* const out, int out_stride) {
+  int lines = mb_h;
+  uint8_t* row_out = out;
+  while (lines-- > 0) {
+    VP8LConvertFromBGRA((const uint32_t*)row_in, mb_w, colorspace, row_out);
+    row_in += in_stride;
+    row_out += out_stride;
+  }
+  return mb_h;  // Num rows out == num rows in.
+}
+
+//------------------------------------------------------------------------------
+// Export to YUVA
+
+// TODO(skal): should be in yuv.c
+static void ConvertToYUVA(const uint32_t* const src, int width, int y_pos,
+                          const WebPDecBuffer* const output) {
+  const WebPYUVABuffer* const buf = &output->u.YUVA;
+  // first, the luma plane
+  {
+    int i;
+    uint8_t* const y = buf->y + y_pos * buf->y_stride;
+    for (i = 0; i < width; ++i) {
+      const uint32_t p = src[i];
+      y[i] = VP8RGBToY((p >> 16) & 0xff, (p >> 8) & 0xff, (p >> 0) & 0xff,
+                       YUV_HALF);
+    }
+  }
+
+  // then U/V planes
+  {
+    uint8_t* const u = buf->u + (y_pos >> 1) * buf->u_stride;
+    uint8_t* const v = buf->v + (y_pos >> 1) * buf->v_stride;
+    const int uv_width = width >> 1;
+    int i;
+    for (i = 0; i < uv_width; ++i) {
+      const uint32_t v0 = src[2 * i + 0];
+      const uint32_t v1 = src[2 * i + 1];
+      // VP8RGBToU/V expects four accumulated pixels. Hence we need to
+      // scale r/g/b value by a factor 2. We just shift v0/v1 one bit less.
+      const int r = ((v0 >> 15) & 0x1fe) + ((v1 >> 15) & 0x1fe);
+      const int g = ((v0 >>  7) & 0x1fe) + ((v1 >>  7) & 0x1fe);
+      const int b = ((v0 <<  1) & 0x1fe) + ((v1 <<  1) & 0x1fe);
+      if (!(y_pos & 1)) {  // even lines: store values
+        u[i] = VP8RGBToU(r, g, b, YUV_HALF << 2);
+        v[i] = VP8RGBToV(r, g, b, YUV_HALF << 2);
+      } else {             // odd lines: average with previous values
+        const int tmp_u = VP8RGBToU(r, g, b, YUV_HALF << 2);
+        const int tmp_v = VP8RGBToV(r, g, b, YUV_HALF << 2);
+        // Approximated average-of-four. But it's an acceptable diff.
+        u[i] = (u[i] + tmp_u + 1) >> 1;
+        v[i] = (v[i] + tmp_v + 1) >> 1;
+      }
+    }
+    if (width & 1) {       // last pixel
+      const uint32_t v0 = src[2 * i + 0];
+      const int r = (v0 >> 14) & 0x3fc;
+      const int g = (v0 >>  6) & 0x3fc;
+      const int b = (v0 <<  2) & 0x3fc;
+      if (!(y_pos & 1)) {  // even lines
+        u[i] = VP8RGBToU(r, g, b, YUV_HALF << 2);
+        v[i] = VP8RGBToV(r, g, b, YUV_HALF << 2);
+      } else {             // odd lines (note: we could just skip this)
+        const int tmp_u = VP8RGBToU(r, g, b, YUV_HALF << 2);
+        const int tmp_v = VP8RGBToV(r, g, b, YUV_HALF << 2);
+        u[i] = (u[i] + tmp_u + 1) >> 1;
+        v[i] = (v[i] + tmp_v + 1) >> 1;
+      }
+    }
+  }
+  // Lastly, store alpha if needed.
+  if (buf->a != NULL) {
+    int i;
+    uint8_t* const a = buf->a + y_pos * buf->a_stride;
+    for (i = 0; i < width; ++i) a[i] = (src[i] >> 24);
+  }
+}
+
+static int ExportYUVA(const VP8LDecoder* const dec, int y_pos) {
+  WebPRescaler* const rescaler = dec->rescaler;
+  uint32_t* const src = (uint32_t*)rescaler->dst;
+  const int dst_width = rescaler->dst_width;
+  int num_lines_out = 0;
+  while (WebPRescalerHasPendingOutput(rescaler)) {
+    WebPRescalerExportRow(rescaler, 0);
+    WebPMultARGBRow(src, dst_width, 1);
+    ConvertToYUVA(src, dst_width, y_pos, dec->output_);
+    ++y_pos;
+    ++num_lines_out;
+  }
+  return num_lines_out;
+}
+
+static int EmitRescaledRowsYUVA(const VP8LDecoder* const dec,
+                                uint8_t* in, int in_stride, int mb_h) {
+  int num_lines_in = 0;
+  int y_pos = dec->last_out_row_;
+  while (num_lines_in < mb_h) {
+    const int lines_left = mb_h - num_lines_in;
+    const int needed_lines = WebPRescaleNeededLines(dec->rescaler, lines_left);
+    WebPMultARGBRows(in, in_stride, dec->rescaler->src_width, needed_lines, 0);
+    WebPRescalerImport(dec->rescaler, lines_left, in, in_stride);
+    num_lines_in += needed_lines;
+    in += needed_lines * in_stride;
+    y_pos += ExportYUVA(dec, y_pos);
+  }
+  return y_pos;
+}
+
+static int EmitRowsYUVA(const VP8LDecoder* const dec,
+                        const uint8_t* in, int in_stride,
+                        int mb_w, int num_rows) {
+  int y_pos = dec->last_out_row_;
+  while (num_rows-- > 0) {
+    ConvertToYUVA((const uint32_t*)in, mb_w, y_pos, dec->output_);
+    in += in_stride;
+    ++y_pos;
+  }
+  return y_pos;
+}
+
+//------------------------------------------------------------------------------
+// Cropping.
+
+// Sets io->mb_y, io->mb_h & io->mb_w according to start row, end row and
+// crop options. Also updates the input data pointer, so that it points to the
+// start of the cropped window. Note that pixels are in ARGB format even if
+// 'in_data' is uint8_t*.
+// Returns true if the crop window is not empty.
+static int SetCropWindow(VP8Io* const io, int y_start, int y_end,
+                         uint8_t** const in_data, int pixel_stride) {
+  assert(y_start < y_end);
+  assert(io->crop_left < io->crop_right);
+  if (y_end > io->crop_bottom) {
+    y_end = io->crop_bottom;  // make sure we don't overflow on last row.
+  }
+  if (y_start < io->crop_top) {
+    const int delta = io->crop_top - y_start;
+    y_start = io->crop_top;
+    *in_data += delta * pixel_stride;
+  }
+  if (y_start >= y_end) return 0;  // Crop window is empty.
+
+  *in_data += io->crop_left * sizeof(uint32_t);
+
+  io->mb_y = y_start - io->crop_top;
+  io->mb_w = io->crop_right - io->crop_left;
+  io->mb_h = y_end - y_start;
+  return 1;  // Non-empty crop window.
+}
+
+//------------------------------------------------------------------------------
+
+static WEBP_INLINE int GetMetaIndex(
+    const uint32_t* const image, int xsize, int bits, int x, int y) {
+  if (bits == 0) return 0;
+  return image[xsize * (y >> bits) + (x >> bits)];
+}
+
+static WEBP_INLINE HTreeGroup* GetHtreeGroupForPos(VP8LMetadata* const hdr,
+                                                   int x, int y) {
+  const int meta_index = GetMetaIndex(hdr->huffman_image_, hdr->huffman_xsize_,
+                                      hdr->huffman_subsample_bits_, x, y);
+  assert(meta_index < hdr->num_htree_groups_);
+  return hdr->htree_groups_ + meta_index;
+}
+
+//------------------------------------------------------------------------------
+// Main loop, with custom row-processing function
+
+typedef void (*ProcessRowsFunc)(VP8LDecoder* const dec, int row);
+
+static void ApplyInverseTransforms(VP8LDecoder* const dec, int num_rows,
+                                   const uint32_t* const rows) {
+  int n = dec->next_transform_;
+  const int cache_pixs = dec->width_ * num_rows;
+  const int start_row = dec->last_row_;
+  const int end_row = start_row + num_rows;
+  const uint32_t* rows_in = rows;
+  uint32_t* const rows_out = dec->argb_cache_;
+
+  // Inverse transforms.
+  // TODO: most transforms only need to operate on the cropped region only.
+  memcpy(rows_out, rows_in, cache_pixs * sizeof(*rows_out));
+  while (n-- > 0) {
+    VP8LTransform* const transform = &dec->transforms_[n];
+    VP8LInverseTransform(transform, start_row, end_row, rows_in, rows_out);
+    rows_in = rows_out;
+  }
+}
+
+// Special method for paletted alpha data.
+static void ApplyInverseTransformsAlpha(VP8LDecoder* const dec, int num_rows,
+                                        const uint8_t* const rows) {
+  const int start_row = dec->last_row_;
+  const int end_row = start_row + num_rows;
+  const uint8_t* rows_in = rows;
+  uint8_t* rows_out = (uint8_t*)dec->io_->opaque + dec->io_->width * start_row;
+  VP8LTransform* const transform = &dec->transforms_[0];
+  assert(dec->next_transform_ == 1);
+  assert(transform->type_ == COLOR_INDEXING_TRANSFORM);
+  VP8LColorIndexInverseTransformAlpha(transform, start_row, end_row, rows_in,
+                                      rows_out);
+}
+
+// Processes (transforms, scales & color-converts) the rows decoded after the
+// last call.
+static void ProcessRows(VP8LDecoder* const dec, int row) {
+  const uint32_t* const rows = dec->pixels_ + dec->width_ * dec->last_row_;
+  const int num_rows = row - dec->last_row_;
+
+  if (num_rows <= 0) return;  // Nothing to be done.
+  ApplyInverseTransforms(dec, num_rows, rows);
+
+  // Emit output.
+  {
+    VP8Io* const io = dec->io_;
+    uint8_t* rows_data = (uint8_t*)dec->argb_cache_;
+    const int in_stride = io->width * sizeof(uint32_t);  // in unit of RGBA
+    if (!SetCropWindow(io, dec->last_row_, row, &rows_data, in_stride)) {
+      // Nothing to output (this time).
+    } else {
+      const WebPDecBuffer* const output = dec->output_;
+      if (output->colorspace < MODE_YUV) {  // convert to RGBA
+        const WebPRGBABuffer* const buf = &output->u.RGBA;
+        uint8_t* const rgba = buf->rgba + dec->last_out_row_ * buf->stride;
+        const int num_rows_out = io->use_scaling ?
+            EmitRescaledRowsRGBA(dec, rows_data, in_stride, io->mb_h,
+                                 rgba, buf->stride) :
+            EmitRows(output->colorspace, rows_data, in_stride,
+                     io->mb_w, io->mb_h, rgba, buf->stride);
+        // Update 'last_out_row_'.
+        dec->last_out_row_ += num_rows_out;
+      } else {                              // convert to YUVA
+        dec->last_out_row_ = io->use_scaling ?
+            EmitRescaledRowsYUVA(dec, rows_data, in_stride, io->mb_h) :
+            EmitRowsYUVA(dec, rows_data, in_stride, io->mb_w, io->mb_h);
+      }
+      assert(dec->last_out_row_ <= output->height);
+    }
+  }
+
+  // Update 'last_row_'.
+  dec->last_row_ = row;
+  assert(dec->last_row_ <= dec->height_);
+}
+
+// Row-processing for the special case when alpha data contains only one
+// transform (color indexing), and trivial non-green literals.
+static int Is8bOptimizable(const VP8LMetadata* const hdr) {
+  int i;
+  if (hdr->color_cache_size_ > 0) return 0;
+  // When the Huffman tree contains only one symbol, we can skip the
+  // call to ReadSymbol() for red/blue/alpha channels.
+  for (i = 0; i < hdr->num_htree_groups_; ++i) {
+    const HuffmanTree* const htrees = hdr->htree_groups_[i].htrees_;
+    if (htrees[RED].num_nodes_ > 1) return 0;
+    if (htrees[BLUE].num_nodes_ > 1) return 0;
+    if (htrees[ALPHA].num_nodes_ > 1) return 0;
+  }
+  return 1;
+}
+
+static void ExtractPalettedAlphaRows(VP8LDecoder* const dec, int row) {
+  const int num_rows = row - dec->last_row_;
+  const uint8_t* const in =
+      (uint8_t*)dec->pixels_ + dec->width_ * dec->last_row_;
+  if (num_rows > 0) {
+    ApplyInverseTransformsAlpha(dec, num_rows, in);
+  }
+  dec->last_row_ = dec->last_out_row_ = row;
+}
+
+static int DecodeAlphaData(VP8LDecoder* const dec, uint8_t* const data,
+                           int width, int height, int last_row) {
+  int ok = 1;
+  int row = dec->last_pixel_ / width;
+  int col = dec->last_pixel_ % width;
+  VP8LBitReader* const br = &dec->br_;
+  VP8LMetadata* const hdr = &dec->hdr_;
+  const HTreeGroup* htree_group = GetHtreeGroupForPos(hdr, col, row);
+  int pos = dec->last_pixel_;         // current position
+  const int end = width * height;     // End of data
+  const int last = width * last_row;  // Last pixel to decode
+  const int len_code_limit = NUM_LITERAL_CODES + NUM_LENGTH_CODES;
+  const int mask = hdr->huffman_mask_;
+  assert(htree_group != NULL);
+  assert(pos < end);
+  assert(last_row <= height);
+  assert(Is8bOptimizable(hdr));
+
+  while (!br->eos_ && pos < last) {
+    int code;
+    // Only update when changing tile.
+    if ((col & mask) == 0) {
+      htree_group = GetHtreeGroupForPos(hdr, col, row);
+    }
+    VP8LFillBitWindow(br);
+    code = ReadSymbol(&htree_group->htrees_[GREEN], br);
+    if (code < NUM_LITERAL_CODES) {  // Literal
+      data[pos] = code;
+      ++pos;
+      ++col;
+      if (col >= width) {
+        col = 0;
+        ++row;
+        if (row % NUM_ARGB_CACHE_ROWS == 0) {
+          ExtractPalettedAlphaRows(dec, row);
+        }
+      }
+    } else if (code < len_code_limit) {  // Backward reference
+      int dist_code, dist;
+      const int length_sym = code - NUM_LITERAL_CODES;
+      const int length = GetCopyLength(length_sym, br);
+      const int dist_symbol = ReadSymbol(&htree_group->htrees_[DIST], br);
+      VP8LFillBitWindow(br);
+      dist_code = GetCopyDistance(dist_symbol, br);
+      dist = PlaneCodeToDistance(width, dist_code);
+      if (pos >= dist && end - pos >= length) {
+        int i;
+        for (i = 0; i < length; ++i) data[pos + i] = data[pos + i - dist];
+      } else {
+        ok = 0;
+        goto End;
+      }
+      pos += length;
+      col += length;
+      while (col >= width) {
+        col -= width;
+        ++row;
+        if (row % NUM_ARGB_CACHE_ROWS == 0) {
+          ExtractPalettedAlphaRows(dec, row);
+        }
+      }
+      if (pos < last && (col & mask)) {
+        htree_group = GetHtreeGroupForPos(hdr, col, row);
+      }
+    } else {  // Not reached
+      ok = 0;
+      goto End;
+    }
+    assert(br->eos_ == VP8LIsEndOfStream(br));
+    ok = !br->error_;
+    if (!ok) goto End;
+  }
+  // Process the remaining rows corresponding to last row-block.
+  ExtractPalettedAlphaRows(dec, row);
+
+ End:
+  if (br->error_ || !ok || (br->eos_ && pos < end)) {
+    ok = 0;
+    dec->status_ = br->eos_ ? VP8_STATUS_SUSPENDED
+                            : VP8_STATUS_BITSTREAM_ERROR;
+  } else {
+    dec->last_pixel_ = (int)pos;
+    if (pos == end) dec->state_ = READ_DATA;
+  }
+  return ok;
+}
+
+static int DecodeImageData(VP8LDecoder* const dec, uint32_t* const data,
+                           int width, int height, int last_row,
+                           ProcessRowsFunc process_func) {
+  int ok = 1;
+  int row = dec->last_pixel_ / width;
+  int col = dec->last_pixel_ % width;
+  VP8LBitReader* const br = &dec->br_;
+  VP8LMetadata* const hdr = &dec->hdr_;
+  HTreeGroup* htree_group = GetHtreeGroupForPos(hdr, col, row);
+  uint32_t* src = data + dec->last_pixel_;
+  uint32_t* last_cached = src;
+  uint32_t* const src_end = data + width * height;     // End of data
+  uint32_t* const src_last = data + width * last_row;  // Last pixel to decode
+  const int len_code_limit = NUM_LITERAL_CODES + NUM_LENGTH_CODES;
+  const int color_cache_limit = len_code_limit + hdr->color_cache_size_;
+  VP8LColorCache* const color_cache =
+      (hdr->color_cache_size_ > 0) ? &hdr->color_cache_ : NULL;
+  const int mask = hdr->huffman_mask_;
+  assert(htree_group != NULL);
+  assert(src < src_end);
+  assert(src_last <= src_end);
+
+  while (!br->eos_ && src < src_last) {
+    int code;
+    // Only update when changing tile. Note we could use this test:
+    // if "((((prev_col ^ col) | prev_row ^ row)) > mask)" -> tile changed
+    // but that's actually slower and needs storing the previous col/row.
+    if ((col & mask) == 0) {
+      htree_group = GetHtreeGroupForPos(hdr, col, row);
+    }
+    VP8LFillBitWindow(br);
+    code = ReadSymbol(&htree_group->htrees_[GREEN], br);
+    if (code < NUM_LITERAL_CODES) {  // Literal
+      int red, green, blue, alpha;
+      red = ReadSymbol(&htree_group->htrees_[RED], br);
+      green = code;
+      VP8LFillBitWindow(br);
+      blue = ReadSymbol(&htree_group->htrees_[BLUE], br);
+      alpha = ReadSymbol(&htree_group->htrees_[ALPHA], br);
+      *src = ((uint32_t)alpha << 24) | (red << 16) | (green << 8) | blue;
+    AdvanceByOne:
+      ++src;
+      ++col;
+      if (col >= width) {
+        col = 0;
+        ++row;
+        if ((row % NUM_ARGB_CACHE_ROWS == 0) && (process_func != NULL)) {
+          process_func(dec, row);
+        }
+        if (color_cache != NULL) {
+          while (last_cached < src) {
+            VP8LColorCacheInsert(color_cache, *last_cached++);
+          }
+        }
+      }
+    } else if (code < len_code_limit) {  // Backward reference
+      int dist_code, dist;
+      const int length_sym = code - NUM_LITERAL_CODES;
+      const int length = GetCopyLength(length_sym, br);
+      const int dist_symbol = ReadSymbol(&htree_group->htrees_[DIST], br);
+      VP8LFillBitWindow(br);
+      dist_code = GetCopyDistance(dist_symbol, br);
+      dist = PlaneCodeToDistance(width, dist_code);
+      if (src - data < (ptrdiff_t)dist || src_end - src < (ptrdiff_t)length) {
+        ok = 0;
+        goto End;
+      } else {
+        int i;
+        for (i = 0; i < length; ++i) src[i] = src[i - dist];
+        src += length;
+      }
+      col += length;
+      while (col >= width) {
+        col -= width;
+        ++row;
+        if ((row % NUM_ARGB_CACHE_ROWS == 0) && (process_func != NULL)) {
+          process_func(dec, row);
+        }
+      }
+      if (src < src_end) {
+        if (col & mask) htree_group = GetHtreeGroupForPos(hdr, col, row);
+        if (color_cache != NULL) {
+          while (last_cached < src) {
+            VP8LColorCacheInsert(color_cache, *last_cached++);
+          }
+        }
+      }
+    } else if (code < color_cache_limit) {  // Color cache
+      const int key = code - len_code_limit;
+      assert(color_cache != NULL);
+      while (last_cached < src) {
+        VP8LColorCacheInsert(color_cache, *last_cached++);
+      }
+      *src = VP8LColorCacheLookup(color_cache, key);
+      goto AdvanceByOne;
+    } else {  // Not reached
+      ok = 0;
+      goto End;
+    }
+    assert(br->eos_ == VP8LIsEndOfStream(br));
+    ok = !br->error_;
+    if (!ok) goto End;
+  }
+  // Process the remaining rows corresponding to last row-block.
+  if (process_func != NULL) process_func(dec, row);
+
+ End:
+  if (br->error_ || !ok || (br->eos_ && src < src_end)) {
+    ok = 0;
+    dec->status_ = br->eos_ ? VP8_STATUS_SUSPENDED
+                            : VP8_STATUS_BITSTREAM_ERROR;
+  } else {
+    dec->last_pixel_ = (int)(src - data);
+    if (src == src_end) dec->state_ = READ_DATA;
+  }
+  return ok;
+}
+
+// -----------------------------------------------------------------------------
+// VP8LTransform
+
+static void ClearTransform(VP8LTransform* const transform) {
+  WebPSafeFree(transform->data_);
+  transform->data_ = NULL;
+}
+
+// For security reason, we need to remap the color map to span
+// the total possible bundled values, and not just the num_colors.
+static int ExpandColorMap(int num_colors, VP8LTransform* const transform) {
+  int i;
+  const int final_num_colors = 1 << (8 >> transform->bits_);
+  uint32_t* const new_color_map =
+      (uint32_t*)WebPSafeMalloc((uint64_t)final_num_colors,
+                                sizeof(*new_color_map));
+  if (new_color_map == NULL) {
+    return 0;
+  } else {
+    uint8_t* const data = (uint8_t*)transform->data_;
+    uint8_t* const new_data = (uint8_t*)new_color_map;
+    new_color_map[0] = transform->data_[0];
+    for (i = 4; i < 4 * num_colors; ++i) {
+      // Equivalent to AddPixelEq(), on a byte-basis.
+      new_data[i] = (data[i] + new_data[i - 4]) & 0xff;
+    }
+    for (; i < 4 * final_num_colors; ++i)
+      new_data[i] = 0;  // black tail.
+    WebPSafeFree(transform->data_);
+    transform->data_ = new_color_map;
+  }
+  return 1;
+}
+
+static int ReadTransform(int* const xsize, int const* ysize,
+                         VP8LDecoder* const dec) {
+  int ok = 1;
+  VP8LBitReader* const br = &dec->br_;
+  VP8LTransform* transform = &dec->transforms_[dec->next_transform_];
+  const VP8LImageTransformType type =
+      (VP8LImageTransformType)VP8LReadBits(br, 2);
+
+  // Each transform type can only be present once in the stream.
+  if (dec->transforms_seen_ & (1U << type)) {
+    return 0;  // Already there, let's not accept the second same transform.
+  }
+  dec->transforms_seen_ |= (1U << type);
+
+  transform->type_ = type;
+  transform->xsize_ = *xsize;
+  transform->ysize_ = *ysize;
+  transform->data_ = NULL;
+  ++dec->next_transform_;
+  assert(dec->next_transform_ <= NUM_TRANSFORMS);
+
+  switch (type) {
+    case PREDICTOR_TRANSFORM:
+    case CROSS_COLOR_TRANSFORM:
+      transform->bits_ = VP8LReadBits(br, 3) + 2;
+      ok = DecodeImageStream(VP8LSubSampleSize(transform->xsize_,
+                                               transform->bits_),
+                             VP8LSubSampleSize(transform->ysize_,
+                                               transform->bits_),
+                             0, dec, &transform->data_);
+      break;
+    case COLOR_INDEXING_TRANSFORM: {
+       const int num_colors = VP8LReadBits(br, 8) + 1;
+       const int bits = (num_colors > 16) ? 0
+                      : (num_colors > 4) ? 1
+                      : (num_colors > 2) ? 2
+                      : 3;
+       *xsize = VP8LSubSampleSize(transform->xsize_, bits);
+       transform->bits_ = bits;
+       ok = DecodeImageStream(num_colors, 1, 0, dec, &transform->data_);
+       ok = ok && ExpandColorMap(num_colors, transform);
+      break;
+    }
+    case SUBTRACT_GREEN:
+      break;
+    default:
+      assert(0);    // can't happen
+      break;
+  }
+
+  return ok;
+}
+
+// -----------------------------------------------------------------------------
+// VP8LMetadata
+
+static void InitMetadata(VP8LMetadata* const hdr) {
+  assert(hdr);
+  memset(hdr, 0, sizeof(*hdr));
+}
+
+static void ClearMetadata(VP8LMetadata* const hdr) {
+  assert(hdr);
+
+  WebPSafeFree(hdr->huffman_image_);
+  VP8LHtreeGroupsFree(hdr->htree_groups_, hdr->num_htree_groups_);
+  VP8LColorCacheClear(&hdr->color_cache_);
+  InitMetadata(hdr);
+}
+
+// -----------------------------------------------------------------------------
+// VP8LDecoder
+
+VP8LDecoder* VP8LNew(void) {
+  VP8LDecoder* const dec = (VP8LDecoder*)WebPSafeCalloc(1ULL, sizeof(*dec));
+  if (dec == NULL) return NULL;
+  dec->status_ = VP8_STATUS_OK;
+  dec->action_ = READ_DIM;
+  dec->state_ = READ_DIM;
+
+  VP8LDspInit();  // Init critical function pointers.
+
+  return dec;
+}
+
+void VP8LClear(VP8LDecoder* const dec) {
+  int i;
+  if (dec == NULL) return;
+  ClearMetadata(&dec->hdr_);
+
+  WebPSafeFree(dec->pixels_);
+  dec->pixels_ = NULL;
+  for (i = 0; i < dec->next_transform_; ++i) {
+    ClearTransform(&dec->transforms_[i]);
+  }
+  dec->next_transform_ = 0;
+  dec->transforms_seen_ = 0;
+
+  WebPSafeFree(dec->rescaler_memory);
+  dec->rescaler_memory = NULL;
+
+  dec->output_ = NULL;   // leave no trace behind
+}
+
+void VP8LDelete(VP8LDecoder* const dec) {
+  if (dec != NULL) {
+    VP8LClear(dec);
+    WebPSafeFree(dec);
+  }
+}
+
+static void UpdateDecoder(VP8LDecoder* const dec, int width, int height) {
+  VP8LMetadata* const hdr = &dec->hdr_;
+  const int num_bits = hdr->huffman_subsample_bits_;
+  dec->width_ = width;
+  dec->height_ = height;
+
+  hdr->huffman_xsize_ = VP8LSubSampleSize(width, num_bits);
+  hdr->huffman_mask_ = (num_bits == 0) ? ~0 : (1 << num_bits) - 1;
+}
+
+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->error_;
+
+ End:
+
+  if (!ok) {
+    WebPSafeFree(data);
+    ClearMetadata(hdr);
+    // If not enough data (br.eos_) resulted in BIT_STREAM_ERROR, update the
+    // status appropriately.
+    if (dec->status_ == VP8_STATUS_BITSTREAM_ERROR && dec->br_.eos_) {
+      dec->status_ = VP8_STATUS_SUSPENDED;
+    }
+  } 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;
+}
+
+//------------------------------------------------------------------------------
+// Allocate internal buffers dec->pixels_ and dec->argb_cache_.
+static int AllocateInternalBuffers32b(VP8LDecoder* const dec, int final_width) {
+  const uint64_t num_pixels = (uint64_t)dec->width_ * dec->height_;
+  // Scratch buffer corresponding to top-prediction row for transforming the
+  // first row in the row-blocks. Not needed for paletted alpha.
+  const uint64_t cache_top_pixels = (uint16_t)final_width;
+  // Scratch buffer for temporary BGRA storage. Not needed for paletted alpha.
+  const uint64_t cache_pixels = (uint64_t)final_width * NUM_ARGB_CACHE_ROWS;
+  const uint64_t total_num_pixels =
+      num_pixels + cache_top_pixels + cache_pixels;
+
+  assert(dec->width_ <= final_width);
+  dec->pixels_ = (uint32_t*)WebPSafeMalloc(total_num_pixels, sizeof(uint32_t));
+  if (dec->pixels_ == NULL) {
+    dec->argb_cache_ = NULL;    // for sanity check
+    dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
+    return 0;
+  }
+  dec->argb_cache_ = dec->pixels_ + num_pixels + cache_top_pixels;
+  return 1;
+}
+
+static int AllocateInternalBuffers8b(VP8LDecoder* const dec) {
+  const uint64_t total_num_pixels = (uint64_t)dec->width_ * dec->height_;
+  dec->argb_cache_ = NULL;    // for sanity check
+  dec->pixels_ = (uint32_t*)WebPSafeMalloc(total_num_pixels, sizeof(uint8_t));
+  if (dec->pixels_ == NULL) {
+    dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
+    return 0;
+  }
+  return 1;
+}
+
+//------------------------------------------------------------------------------
+
+// Special row-processing that only stores the alpha data.
+static void ExtractAlphaRows(VP8LDecoder* const dec, int row) {
+  const int num_rows = row - dec->last_row_;
+  const uint32_t* const in = dec->pixels_ + dec->width_ * dec->last_row_;
+
+  if (num_rows <= 0) return;  // Nothing to be done.
+  ApplyInverseTransforms(dec, num_rows, in);
+
+  // Extract alpha (which is stored in the green plane).
+  {
+    const int width = dec->io_->width;      // the final width (!= dec->width_)
+    const int cache_pixs = width * num_rows;
+    uint8_t* const dst = (uint8_t*)dec->io_->opaque + width * dec->last_row_;
+    const uint32_t* const src = dec->argb_cache_;
+    int i;
+    for (i = 0; i < cache_pixs; ++i) dst[i] = (src[i] >> 8) & 0xff;
+  }
+  dec->last_row_ = dec->last_out_row_ = row;
+}
+
+int VP8LDecodeAlphaHeader(ALPHDecoder* const alph_dec,
+                          const uint8_t* const data, size_t data_size,
+                          uint8_t* const output) {
+  int ok = 0;
+  VP8LDecoder* dec;
+  VP8Io* io;
+  assert(alph_dec != NULL);
+  alph_dec->vp8l_dec_ = VP8LNew();
+  if (alph_dec->vp8l_dec_ == NULL) return 0;
+  dec = alph_dec->vp8l_dec_;
+
+  dec->width_ = alph_dec->width_;
+  dec->height_ = alph_dec->height_;
+  dec->io_ = &alph_dec->io_;
+  io = dec->io_;
+
+  VP8InitIo(io);
+  WebPInitCustomIo(NULL, io);  // Just a sanity Init. io won't be used.
+  io->opaque = output;
+  io->width = alph_dec->width_;
+  io->height = alph_dec->height_;
+
+  dec->status_ = VP8_STATUS_OK;
+  VP8LInitBitReader(&dec->br_, data, data_size);
+
+  dec->action_ = READ_HDR;
+  if (!DecodeImageStream(alph_dec->width_, alph_dec->height_, 1, dec, NULL)) {
+    goto Err;
+  }
+
+  // Special case: if alpha data uses only the color indexing transform and
+  // doesn't use color cache (a frequent case), we will use DecodeAlphaData()
+  // method that only needs allocation of 1 byte per pixel (alpha channel).
+  if (dec->next_transform_ == 1 &&
+      dec->transforms_[0].type_ == COLOR_INDEXING_TRANSFORM &&
+      Is8bOptimizable(&dec->hdr_)) {
+    alph_dec->use_8b_decode = 1;
+    ok = AllocateInternalBuffers8b(dec);
+  } else {
+    // Allocate internal buffers (note that dec->width_ may have changed here).
+    alph_dec->use_8b_decode = 0;
+    ok = AllocateInternalBuffers32b(dec, alph_dec->width_);
+  }
+
+  if (!ok) goto Err;
+
+  dec->action_ = READ_DATA;
+  return 1;
+
+ Err:
+  VP8LDelete(alph_dec->vp8l_dec_);
+  alph_dec->vp8l_dec_ = NULL;
+  return 0;
+}
+
+int VP8LDecodeAlphaImageStream(ALPHDecoder* const alph_dec, int last_row) {
+  VP8LDecoder* const dec = alph_dec->vp8l_dec_;
+  assert(dec != NULL);
+  assert(dec->action_ == READ_DATA);
+  assert(last_row <= dec->height_);
+
+  if (dec->last_pixel_ == dec->width_ * dec->height_) {
+    return 1;  // done
+  }
+
+  // Decode (with special row processing).
+  return alph_dec->use_8b_decode ?
+      DecodeAlphaData(dec, (uint8_t*)dec->pixels_, dec->width_, dec->height_,
+                      last_row) :
+      DecodeImageData(dec, dec->pixels_, dec->width_, dec->height_,
+                      last_row, ExtractAlphaRows);
+}
+
+//------------------------------------------------------------------------------
+
+int VP8LDecodeHeader(VP8LDecoder* const dec, VP8Io* const io) {
+  int width, height, has_alpha;
+
+  if (dec == NULL) return 0;
+  if (io == NULL) {
+    dec->status_ = VP8_STATUS_INVALID_PARAM;
+    return 0;
+  }
+
+  dec->io_ = io;
+  dec->status_ = VP8_STATUS_OK;
+  VP8LInitBitReader(&dec->br_, io->data, io->data_size);
+  if (!ReadImageInfo(&dec->br_, &width, &height, &has_alpha)) {
+    dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
+    goto Error;
+  }
+  dec->state_ = READ_DIM;
+  io->width = width;
+  io->height = height;
+
+  dec->action_ = READ_HDR;
+  if (!DecodeImageStream(width, height, 1, dec, NULL)) goto Error;
+  return 1;
+
+ Error:
+  VP8LClear(dec);
+  assert(dec->status_ != VP8_STATUS_OK);
+  return 0;
+}
+
+int VP8LDecodeImage(VP8LDecoder* const dec) {
+  VP8Io* io = NULL;
+  WebPDecParams* params = NULL;
+
+  // Sanity checks.
+  if (dec == NULL) return 0;
+
+  dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
+  assert(dec->hdr_.htree_groups_ != NULL);
+  assert(dec->hdr_.num_htree_groups_ > 0);
+
+  io = dec->io_;
+  assert(io != NULL);
+  params = (WebPDecParams*)io->opaque;
+  assert(params != NULL);
+  dec->output_ = params->output;
+  assert(dec->output_ != NULL);
+
+  // Initialization.
+  if (!WebPIoInitFromOptions(params->options, io, MODE_BGRA)) {
+    dec->status_ = VP8_STATUS_INVALID_PARAM;
+    goto Err;
+  }
+
+  if (!AllocateInternalBuffers32b(dec, io->width)) goto Err;
+
+  if (io->use_scaling && !AllocateAndInitRescaler(dec, io)) goto Err;
+
+  if (io->use_scaling || WebPIsPremultipliedMode(dec->output_->colorspace)) {
+    // need the alpha-multiply functions for premultiplied output or rescaling
+    WebPInitAlphaProcessing();
+  }
+
+  // Decode.
+  dec->action_ = READ_DATA;
+  if (!DecodeImageData(dec, dec->pixels_, dec->width_, dec->height_,
+                       dec->height_, ProcessRows)) {
+    goto Err;
+  }
+
+  // Cleanup.
+  params->last_y = dec->last_out_row_;
+  VP8LClear(dec);
+  return 1;
+
+ Err:
+  VP8LClear(dec);
+  assert(dec->status_ != VP8_STATUS_OK);
+  return 0;
+}
+
+//------------------------------------------------------------------------------