third_party/libwebp/dec/vp8l.c

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This source file includes following definitions.
VP8LCheckSignature
ReadImageInfo
VP8LGetInfo
GetCopyDistance
GetCopyLength
PlaneCodeToDistance
ReadSymbol
ReadHuffmanCodeLengths
ReadHuffmanCode
DeleteHtreeGroups
ReadHuffmanCodes
AllocateAndInitRescaler
Export
EmitRescaledRowsRGBA
EmitRows
ConvertToYUVA
ExportYUVA
EmitRescaledRowsYUVA
EmitRowsYUVA
SetCropWindow
GetMetaIndex
GetHtreeGroupForPos
ApplyInverseTransforms
ApplyInverseTransformsAlpha
ProcessRows
Is8bOptimizable
ExtractPalettedAlphaRows
DecodeAlphaData
DecodeImageData
ClearTransform
ExpandColorMap
ReadTransform
InitMetadata
ClearMetadata
VP8LNew
VP8LClear
VP8LDelete
UpdateDecoder
DecodeImageStream
AllocateInternalBuffers32b
AllocateInternalBuffers8b
ExtractAlphaRows
VP8LDecodeAlphaHeader
VP8LDecodeAlphaImageStream
VP8LDecodeHeader
VP8LDecodeImage
// 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/lossless.h"
#include "../dsp/yuv.h"
#include "../utils/alpha_processing.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;

  if (!HuffmanTreeBuildImplicit(&tree, code_length_code_lengths,
                                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:
  HuffmanTreeRelease(&tree);
  return ok;
}

static int ReadHuffmanCode(int alphabet_size, VP8LDecoder* const dec,
                           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];
    int code_lengths[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 = HuffmanTreeBuildExplicit(tree, code_lengths, codes, symbols,
                                  alphabet_size, num_symbols);
  } else {  // Decode Huffman-coded code lengths.
    int* code_lengths = NULL;
    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;
    }

    code_lengths =
        (int*)WebPSafeCalloc((uint64_t)alphabet_size, sizeof(*code_lengths));
    if (code_lengths == NULL) {
      dec->status_ = VP8_STATUS_OUT_OF_MEMORY;
      return 0;
    }

    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);
    if (ok) {
      ok = HuffmanTreeBuildImplicit(tree, code_lengths, alphabet_size);
    }
    free(code_lengths);
  }
  ok = ok && !br->error_;
  if (!ok) {
    dec->status_ = VP8_STATUS_BITSTREAM_ERROR;
    return 0;
  }
  return 1;
}

static void DeleteHtreeGroups(HTreeGroup* htree_groups, int num_htree_groups) {
  if (htree_groups != NULL) {
    int i, j;
    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) {
        HuffmanTreeRelease(&htrees[j]);
      }
    }
    free(htree_groups);
  }
}

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;

  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;

  assert(num_htree_groups <= 0x10000);
  htree_groups =
      (HTreeGroup*)WebPSafeCalloc((uint64_t)num_htree_groups,
                                  sizeof(*htree_groups));
  if (htree_groups == 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];
      if (j == 0 && color_cache_bits > 0) {
        alphabet_size += 1 << color_cache_bits;
      }
      if (!ReadHuffmanCode(alphabet_size, dec, htrees + j)) goto Error;
    }
  }

  // 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:
  free(huffman_image);
  DeleteHtreeGroups(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);
    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

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);
    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;
    }
    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 = (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_last) {
        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;
    }
    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) {
  free(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.
    free(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);

  free(hdr->huffman_image_);
  DeleteHtreeGroups(hdr->htree_groups_, hdr->num_htree_groups_);
  VP8LColorCacheClear(&hdr->color_cache_);
  InitMetadata(hdr);
}

// -----------------------------------------------------------------------------
// VP8LDecoder

VP8LDecoder* VP8LNew(void) {
  VP8LDecoder* const dec = (VP8LDecoder*)calloc(1, 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_);

  free(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;

  free(dec->rescaler_memory);
  dec->rescaler_memory = NULL;

  dec->output_ = NULL;   // leave no trace behind
}

void VP8LDelete(VP8LDecoder* const dec) {
  if (dec != NULL) {
    VP8LClear(dec);
    free(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) {
    free(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;

  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;

  // 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;
}

//------------------------------------------------------------------------------
/* [<][>][^][v][top][bottom][index][help] */
root/third_party/libwebp/dec/vp8l.c

DEFINITIONS
