libwebp: update snapshot to v0.2.0-rc1

third_party/libwebp/dsp/lossless.c

Index: third_party/libwebp/dsp/lossless.c
diff --git a/third_party/libwebp/dsp/lossless.c b/third_party/libwebp/dsp/lossless.c
new file mode 100644
index 0000000000000000000000000000000000000000..472e641e450dd24ba80f11271abfe9ca9d929644
--- /dev/null
+++ b/third_party/libwebp/dsp/lossless.c
@@ -0,0 +1,1124 @@
+// Copyright 2012 Google Inc. All Rights Reserved.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// Image transforms and color space conversion methods for lossless decoder.
+//
+// Authors: Vikas Arora (vikaas.arora@gmail.com)
+//          Jyrki Alakuijala (jyrki@google.com)
+//          Urvang Joshi (urvang@google.com)
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+#include <math.h>
+#include <stdlib.h>
+#include "./lossless.h"
+#include "../dec/vp8li.h"
+#include "../dsp/yuv.h"
+#include "../dsp/dsp.h"
+#include "../enc/histogram.h"
+
+#define MAX_DIFF_COST (1e30f)
+
+// lookup table for small values of log2(int)
+#define APPROX_LOG_MAX  4096
+#define LOG_2_RECIPROCAL 1.44269504088896338700465094007086
+#define LOG_LOOKUP_IDX_MAX 256
+static const float kLog2Table[LOG_LOOKUP_IDX_MAX] = {
+  0.0000000000000000f, 0.0000000000000000f,
+  1.0000000000000000f, 1.5849625007211560f,
+  2.0000000000000000f, 2.3219280948873621f,
+  2.5849625007211560f, 2.8073549220576041f,
+  3.0000000000000000f, 3.1699250014423121f,
+  3.3219280948873621f, 3.4594316186372973f,
+  3.5849625007211560f, 3.7004397181410921f,
+  3.8073549220576041f, 3.9068905956085187f,
+  4.0000000000000000f, 4.0874628412503390f,
+  4.1699250014423121f, 4.2479275134435852f,
+  4.3219280948873626f, 4.3923174227787606f,
+  4.4594316186372973f, 4.5235619560570130f,
+  4.5849625007211560f, 4.6438561897747243f,
+  4.7004397181410917f, 4.7548875021634682f,
+  4.8073549220576037f, 4.8579809951275718f,
+  4.9068905956085187f, 4.9541963103868749f,
+  5.0000000000000000f, 5.0443941193584533f,
+  5.0874628412503390f, 5.1292830169449663f,
+  5.1699250014423121f, 5.2094533656289501f,
+  5.2479275134435852f, 5.2854022188622487f,
+  5.3219280948873626f, 5.3575520046180837f,
+  5.3923174227787606f, 5.4262647547020979f,
+  5.4594316186372973f, 5.4918530963296747f,
+  5.5235619560570130f, 5.5545888516776376f,
+  5.5849625007211560f, 5.6147098441152083f,
+  5.6438561897747243f, 5.6724253419714951f,
+  5.7004397181410917f, 5.7279204545631987f,
+  5.7548875021634682f, 5.7813597135246599f,
+  5.8073549220576037f, 5.8328900141647412f,
+  5.8579809951275718f, 5.8826430493618415f,
+  5.9068905956085187f, 5.9307373375628866f,
+  5.9541963103868749f, 5.9772799234999167f,
+  6.0000000000000000f, 6.0223678130284543f,
+  6.0443941193584533f, 6.0660891904577720f,
+  6.0874628412503390f, 6.1085244567781691f,
+  6.1292830169449663f, 6.1497471195046822f,
+  6.1699250014423121f, 6.1898245588800175f,
+  6.2094533656289501f, 6.2288186904958804f,
+  6.2479275134435852f, 6.2667865406949010f,
+  6.2854022188622487f, 6.3037807481771030f,
+  6.3219280948873626f, 6.3398500028846243f,
+  6.3575520046180837f, 6.3750394313469245f,
+  6.3923174227787606f, 6.4093909361377017f,
+  6.4262647547020979f, 6.4429434958487279f,
+  6.4594316186372973f, 6.4757334309663976f,
+  6.4918530963296747f, 6.5077946401986963f,
+  6.5235619560570130f, 6.5391588111080309f,
+  6.5545888516776376f, 6.5698556083309478f,
+  6.5849625007211560f, 6.5999128421871278f,
+  6.6147098441152083f, 6.6293566200796094f,
+  6.6438561897747243f, 6.6582114827517946f,
+  6.6724253419714951f, 6.6865005271832185f,
+  6.7004397181410917f, 6.7142455176661224f,
+  6.7279204545631987f, 6.7414669864011464f,
+  6.7548875021634682f, 6.7681843247769259f,
+  6.7813597135246599f, 6.7944158663501061f,
+  6.8073549220576037f, 6.8201789624151878f,
+  6.8328900141647412f, 6.8454900509443747f,
+  6.8579809951275718f, 6.8703647195834047f,
+  6.8826430493618415f, 6.8948177633079437f,
+  6.9068905956085187f, 6.9188632372745946f,
+  6.9307373375628866f, 6.9425145053392398f,
+  6.9541963103868749f, 6.9657842846620869f,
+  6.9772799234999167f, 6.9886846867721654f,
+  7.0000000000000000f, 7.0112272554232539f,
+  7.0223678130284543f, 7.0334230015374501f,
+  7.0443941193584533f, 7.0552824355011898f,
+  7.0660891904577720f, 7.0768155970508308f,
+  7.0874628412503390f, 7.0980320829605263f,
+  7.1085244567781691f, 7.1189410727235076f,
+  7.1292830169449663f, 7.1395513523987936f,
+  7.1497471195046822f, 7.1598713367783890f,
+  7.1699250014423121f, 7.1799090900149344f,
+  7.1898245588800175f, 7.1996723448363644f,
+  7.2094533656289501f, 7.2191685204621611f,
+  7.2288186904958804f, 7.2384047393250785f,
+  7.2479275134435852f, 7.2573878426926521f,
+  7.2667865406949010f, 7.2761244052742375f,
+  7.2854022188622487f, 7.2946207488916270f,
+  7.3037807481771030f, 7.3128829552843557f,
+  7.3219280948873626f, 7.3309168781146167f,
+  7.3398500028846243f, 7.3487281542310771f,
+  7.3575520046180837f, 7.3663222142458160f,
+  7.3750394313469245f, 7.3837042924740519f,
+  7.3923174227787606f, 7.4008794362821843f,
+  7.4093909361377017f, 7.4178525148858982f,
+  7.4262647547020979f, 7.4346282276367245f,
+  7.4429434958487279f, 7.4512111118323289f,
+  7.4594316186372973f, 7.4676055500829976f,
+  7.4757334309663976f, 7.4838157772642563f,
+  7.4918530963296747f, 7.4998458870832056f,
+  7.5077946401986963f, 7.5156998382840427f,
+  7.5235619560570130f, 7.5313814605163118f,
+  7.5391588111080309f, 7.5468944598876364f,
+  7.5545888516776376f, 7.5622424242210728f,
+  7.5698556083309478f, 7.5774288280357486f,
+  7.5849625007211560f, 7.5924570372680806f,
+  7.5999128421871278f, 7.6073303137496104f,
+  7.6147098441152083f, 7.6220518194563764f,
+  7.6293566200796094f, 7.6366246205436487f,
+  7.6438561897747243f, 7.6510516911789281f,
+  7.6582114827517946f, 7.6653359171851764f,
+  7.6724253419714951f, 7.6794800995054464f,
+  7.6865005271832185f, 7.6934869574993252f,
+  7.7004397181410917f, 7.7073591320808825f,
+  7.7142455176661224f, 7.7210991887071855f,
+  7.7279204545631987f, 7.7347096202258383f,
+  7.7414669864011464f, 7.7481928495894605f,
+  7.7548875021634682f, 7.7615512324444795f,
+  7.7681843247769259f, 7.7747870596011736f,
+  7.7813597135246599f, 7.7879025593914317f,
+  7.7944158663501061f, 7.8008998999203047f,
+  7.8073549220576037f, 7.8137811912170374f,
+  7.8201789624151878f, 7.8265484872909150f,
+  7.8328900141647412f, 7.8392037880969436f,
+  7.8454900509443747f, 7.8517490414160571f,
+  7.8579809951275718f, 7.8641861446542797f,
+  7.8703647195834047f, 7.8765169465649993f,
+  7.8826430493618415f, 7.8887432488982591f,
+  7.8948177633079437f, 7.9008668079807486f,
+  7.9068905956085187f, 7.9128893362299619f,
+  7.9188632372745946f, 7.9248125036057812f,
+  7.9307373375628866f, 7.9366379390025709f,
+  7.9425145053392398f, 7.9483672315846778f,
+  7.9541963103868749f, 7.9600019320680805f,
+  7.9657842846620869f, 7.9715435539507719f,
+  7.9772799234999167f, 7.9829935746943103f,
+  7.9886846867721654f, 7.9943534368588577f
+};
+
+float VP8LFastLog2(int v) {
+  if (v < LOG_LOOKUP_IDX_MAX) {
+    return kLog2Table[v];
+  } else if (v < APPROX_LOG_MAX) {
+    int log_cnt = 0;
+    while (v >= LOG_LOOKUP_IDX_MAX) {
+      ++log_cnt;
+      v = v >> 1;
+    }
+    return kLog2Table[v] + (float)log_cnt;
+  } else {
+    return (float)(LOG_2_RECIPROCAL * log((double)v));
+  }
+}
+
+//------------------------------------------------------------------------------
+// Image transforms.
+
+// In-place sum of each component with mod 256.
+static WEBP_INLINE void AddPixelsEq(uint32_t* a, uint32_t b) {
+  const uint32_t alpha_and_green = (*a & 0xff00ff00u) + (b & 0xff00ff00u);
+  const uint32_t red_and_blue = (*a & 0x00ff00ffu) + (b & 0x00ff00ffu);
+  *a = (alpha_and_green & 0xff00ff00u) | (red_and_blue & 0x00ff00ffu);
+}
+
+static WEBP_INLINE uint32_t Average2(uint32_t a0, uint32_t a1) {
+  return (((a0 ^ a1) & 0xfefefefeL) >> 1) + (a0 & a1);
+}
+
+static WEBP_INLINE uint32_t Average3(uint32_t a0, uint32_t a1, uint32_t a2) {
+  return Average2(Average2(a0, a2), a1);
+}
+
+static WEBP_INLINE uint32_t Average4(uint32_t a0, uint32_t a1,
+                                     uint32_t a2, uint32_t a3) {
+  return Average2(Average2(a0, a1), Average2(a2, a3));
+}
+
+static WEBP_INLINE uint32_t Clip255(uint32_t a) {
+  if (a < 256) {
+    return a;
+  }
+  // return 0, when a is a negative integer.
+  // return 255, when a is positive.
+  return ~a >> 24;
+}
+
+static WEBP_INLINE int AddSubtractComponentFull(int a, int b, int c) {
+  return Clip255(a + b - c);
+}
+
+static WEBP_INLINE uint32_t ClampedAddSubtractFull(uint32_t c0, uint32_t c1,
+                                                   uint32_t c2) {
+  const int a = AddSubtractComponentFull(c0 >> 24, c1 >> 24, c2 >> 24);
+  const int r = AddSubtractComponentFull((c0 >> 16) & 0xff,
+                                         (c1 >> 16) & 0xff,
+                                         (c2 >> 16) & 0xff);
+  const int g = AddSubtractComponentFull((c0 >> 8) & 0xff,
+                                         (c1 >> 8) & 0xff,
+                                         (c2 >> 8) & 0xff);
+  const int b = AddSubtractComponentFull(c0 & 0xff, c1 & 0xff, c2 & 0xff);
+  return (a << 24) | (r << 16) | (g << 8) | b;
+}
+
+static WEBP_INLINE int AddSubtractComponentHalf(int a, int b) {
+  return Clip255(a + (a - b) / 2);
+}
+
+static WEBP_INLINE uint32_t ClampedAddSubtractHalf(uint32_t c0, uint32_t c1,
+                                                   uint32_t c2) {
+  const uint32_t ave = Average2(c0, c1);
+  const int a = AddSubtractComponentHalf(ave >> 24, c2 >> 24);
+  const int r = AddSubtractComponentHalf((ave >> 16) & 0xff, (c2 >> 16) & 0xff);
+  const int g = AddSubtractComponentHalf((ave >> 8) & 0xff, (c2 >> 8) & 0xff);
+  const int b = AddSubtractComponentHalf((ave >> 0) & 0xff, (c2 >> 0) & 0xff);
+  return (a << 24) | (r << 16) | (g << 8) | b;
+}
+
+static WEBP_INLINE int Sub3(int a, int b, int c) {
+  const int pa = b - c;
+  const int pb = a - c;
+  return abs(pa) - abs(pb);
+}
+
+static WEBP_INLINE uint32_t Select(uint32_t a, uint32_t b, uint32_t c) {
+  const int pa_minus_pb =
+      Sub3((a >> 24)       , (b >> 24)       , (c >> 24)       ) +
+      Sub3((a >> 16) & 0xff, (b >> 16) & 0xff, (c >> 16) & 0xff) +
+      Sub3((a >>  8) & 0xff, (b >>  8) & 0xff, (c >>  8) & 0xff) +
+      Sub3((a      ) & 0xff, (b      ) & 0xff, (c      ) & 0xff);
+
+  return (pa_minus_pb <= 0) ? a : b;
+}
+
+//------------------------------------------------------------------------------
+// Predictors
+
+static uint32_t Predictor0(uint32_t left, const uint32_t* const top) {
+  (void)top;
+  (void)left;
+  return ARGB_BLACK;
+}
+static uint32_t Predictor1(uint32_t left, const uint32_t* const top) {
+  (void)top;
+  return left;
+}
+static uint32_t Predictor2(uint32_t left, const uint32_t* const top) {
+  (void)left;
+  return top[0];
+}
+static uint32_t Predictor3(uint32_t left, const uint32_t* const top) {
+  (void)left;
+  return top[1];
+}
+static uint32_t Predictor4(uint32_t left, const uint32_t* const top) {
+  (void)left;
+  return top[-1];
+}
+static uint32_t Predictor5(uint32_t left, const uint32_t* const top) {
+  const uint32_t pred = Average3(left, top[0], top[1]);
+  return pred;
+}
+static uint32_t Predictor6(uint32_t left, const uint32_t* const top) {
+  const uint32_t pred = Average2(left, top[-1]);
+  return pred;
+}
+static uint32_t Predictor7(uint32_t left, const uint32_t* const top) {
+  const uint32_t pred = Average2(left, top[0]);
+  return pred;
+}
+static uint32_t Predictor8(uint32_t left, const uint32_t* const top) {
+  const uint32_t pred = Average2(top[-1], top[0]);
+  (void)left;
+  return pred;
+}
+static uint32_t Predictor9(uint32_t left, const uint32_t* const top) {
+  const uint32_t pred = Average2(top[0], top[1]);
+  (void)left;
+  return pred;
+}
+static uint32_t Predictor10(uint32_t left, const uint32_t* const top) {
+  const uint32_t pred = Average4(left, top[-1], top[0], top[1]);
+  return pred;
+}
+static uint32_t Predictor11(uint32_t left, const uint32_t* const top) {
+  const uint32_t pred = Select(top[0], left, top[-1]);
+  return pred;
+}
+static uint32_t Predictor12(uint32_t left, const uint32_t* const top) {
+  const uint32_t pred = ClampedAddSubtractFull(left, top[0], top[-1]);
+  return pred;
+}
+static uint32_t Predictor13(uint32_t left, const uint32_t* const top) {
+  const uint32_t pred = ClampedAddSubtractHalf(left, top[0], top[-1]);
+  return pred;
+}
+
+typedef uint32_t (*PredictorFunc)(uint32_t left, const uint32_t* const top);
+static const PredictorFunc kPredictors[16] = {
+  Predictor0, Predictor1, Predictor2, Predictor3,
+  Predictor4, Predictor5, Predictor6, Predictor7,
+  Predictor8, Predictor9, Predictor10, Predictor11,
+  Predictor12, Predictor13,
+  Predictor0, Predictor0    // <- padding security sentinels
+};
+
+// TODO(vikasa): Replace 256 etc with defines.
+static float PredictionCostSpatial(const int* counts,
+                                   int weight_0, double exp_val) {
+  const int significant_symbols = 16;
+  const double exp_decay_factor = 0.6;
+  double bits = weight_0 * counts[0];
+  int i;
+  for (i = 1; i < significant_symbols; ++i) {
+    bits += exp_val * (counts[i] + counts[256 - i]);
+    exp_val *= exp_decay_factor;
+  }
+  return (float)(-0.1 * bits);
+}
+
+// Compute the Shanon's entropy: Sum(p*log2(p))
+static float ShannonEntropy(const int* const array, int n) {
+  int i;
+  float retval = 0.f;
+  int sum = 0;
+  for (i = 0; i < n; ++i) {
+    if (array[i] != 0) {
+      sum += array[i];
+      retval -= VP8LFastSLog2(array[i]);
+    }
+  }
+  retval += VP8LFastSLog2(sum);
+  return retval;
+}
+
+static float PredictionCostSpatialHistogram(int accumulated[4][256],
+                                            int tile[4][256]) {
+  int i;
+  int k;
+  int combo[256];
+  double retval = 0;
+  for (i = 0; i < 4; ++i) {
+    const double exp_val = 0.94;
+    retval += PredictionCostSpatial(&tile[i][0], 1, exp_val);
+    retval += ShannonEntropy(&tile[i][0], 256);
+    for (k = 0; k < 256; ++k) {
+      combo[k] = accumulated[i][k] + tile[i][k];
+    }
+    retval += ShannonEntropy(&combo[0], 256);
+  }
+  return (float)retval;
+}
+
+static int GetBestPredictorForTile(int width, int height,
+                                   int tile_x, int tile_y, int bits,
+                                   int accumulated[4][256],
+                                   const uint32_t* const argb_scratch) {
+  const int kNumPredModes = 14;
+  const int col_start = tile_x << bits;
+  const int row_start = tile_y << bits;
+  const int tile_size = 1 << bits;
+  const int ymax = (tile_size <= height - row_start) ?
+      tile_size : height - row_start;
+  const int xmax = (tile_size <= width - col_start) ?
+      tile_size : width - col_start;
+  int histo[4][256];
+  float best_diff = MAX_DIFF_COST;
+  int best_mode = 0;
+
+  int mode;
+  for (mode = 0; mode < kNumPredModes; ++mode) {
+    const uint32_t* current_row = argb_scratch;
+    const PredictorFunc pred_func = kPredictors[mode];
+    float cur_diff;
+    int y;
+    memset(&histo[0][0], 0, sizeof(histo));
+    for (y = 0; y < ymax; ++y) {
+      int x;
+      const int row = row_start + y;
+      const uint32_t* const upper_row = current_row;
+      current_row = upper_row + width;
+      for (x = 0; x < xmax; ++x) {
+        const int col = col_start + x;
+        uint32_t predict;
+        uint32_t predict_diff;
+        if (row == 0) {
+          predict = (col == 0) ? ARGB_BLACK : current_row[col - 1];  // Left.
+        } else if (col == 0) {
+          predict = upper_row[col];  // Top.
+        } else {
+          predict = pred_func(current_row[col - 1], upper_row + col);
+        }
+        predict_diff = VP8LSubPixels(current_row[col], predict);
+        ++histo[0][predict_diff >> 24];
+        ++histo[1][((predict_diff >> 16) & 0xff)];
+        ++histo[2][((predict_diff >> 8) & 0xff)];
+        ++histo[3][(predict_diff & 0xff)];
+      }
+    }
+    cur_diff = PredictionCostSpatialHistogram(accumulated, histo);
+    if (cur_diff < best_diff) {
+      best_diff = cur_diff;
+      best_mode = mode;
+    }
+  }
+
+  return best_mode;
+}
+
+static void CopyTileWithPrediction(int width, int height,
+                                   int tile_x, int tile_y, int bits, int mode,
+                                   const uint32_t* const argb_scratch,
+                                   uint32_t* const argb) {
+  const int col_start = tile_x << bits;
+  const int row_start = tile_y << bits;
+  const int tile_size = 1 << bits;
+  const int ymax = (tile_size <= height - row_start) ?
+      tile_size : height - row_start;
+  const int xmax = (tile_size <= width - col_start) ?
+      tile_size : width - col_start;
+  const PredictorFunc pred_func = kPredictors[mode];
+  const uint32_t* current_row = argb_scratch;
+
+  int y;
+  for (y = 0; y < ymax; ++y) {
+    int x;
+    const int row = row_start + y;
+    const uint32_t* const upper_row = current_row;
+    current_row = upper_row + width;
+    for (x = 0; x < xmax; ++x) {
+      const int col = col_start + x;
+      const int pix = row * width + col;
+      uint32_t predict;
+      if (row == 0) {
+        predict = (col == 0) ? ARGB_BLACK : current_row[col - 1];  // Left.
+      } else if (col == 0) {
+        predict = upper_row[col];  // Top.
+      } else {
+        predict = pred_func(current_row[col - 1], upper_row + col);
+      }
+      argb[pix] = VP8LSubPixels(current_row[col], predict);
+    }
+  }
+}
+
+void VP8LResidualImage(int width, int height, int bits,
+                       uint32_t* const argb, uint32_t* const argb_scratch,
+                       uint32_t* const image) {
+  const int max_tile_size = 1 << bits;
+  const int tiles_per_row = VP8LSubSampleSize(width, bits);
+  const int tiles_per_col = VP8LSubSampleSize(height, bits);
+  uint32_t* const upper_row = argb_scratch;
+  uint32_t* const current_tile_rows = argb_scratch + width;
+  int tile_y;
+  int histo[4][256];
+  memset(histo, 0, sizeof(histo));
+  for (tile_y = 0; tile_y < tiles_per_col; ++tile_y) {
+    const int tile_y_offset = tile_y * max_tile_size;
+    const int this_tile_height =
+        (tile_y < tiles_per_col - 1) ? max_tile_size : height - tile_y_offset;
+    int tile_x;
+    if (tile_y > 0) {
+      memcpy(upper_row, current_tile_rows + (max_tile_size - 1) * width,
+             width * sizeof(*upper_row));
+    }
+    memcpy(current_tile_rows, &argb[tile_y_offset * width],
+           this_tile_height * width * sizeof(*current_tile_rows));
+    for (tile_x = 0; tile_x < tiles_per_row; ++tile_x) {
+      int pred;
+      int y;
+      const int tile_x_offset = tile_x * max_tile_size;
+      int all_x_max = tile_x_offset + max_tile_size;
+      if (all_x_max > width) {
+        all_x_max = width;
+      }
+      pred = GetBestPredictorForTile(width, height, tile_x, tile_y, bits, histo,
+                                     argb_scratch);
+      image[tile_y * tiles_per_row + tile_x] = 0xff000000u | (pred << 8);
+      CopyTileWithPrediction(width, height, tile_x, tile_y, bits, pred,
+                             argb_scratch, argb);
+      for (y = 0; y < max_tile_size; ++y) {
+        int ix;
+        int all_x;
+        int all_y = tile_y_offset + y;
+        if (all_y >= height) {
+          break;
+        }
+        ix = all_y * width + tile_x_offset;
+        for (all_x = tile_x_offset; all_x < all_x_max; ++all_x, ++ix) {
+          const uint32_t a = argb[ix];
+          ++histo[0][a >> 24];
+          ++histo[1][((a >> 16) & 0xff)];
+          ++histo[2][((a >> 8) & 0xff)];
+          ++histo[3][(a & 0xff)];
+        }
+      }
+    }
+  }
+}
+
+// Inverse prediction.
+static void PredictorInverseTransform(const VP8LTransform* const transform,
+                                      int y_start, int y_end, uint32_t* data) {
+  const int width = transform->xsize_;
+  if (y_start == 0) {  // First Row follows the L (mode=1) mode.
+    int x;
+    const uint32_t pred0 = Predictor0(data[-1], NULL);
+    AddPixelsEq(data, pred0);
+    for (x = 1; x < width; ++x) {
+      const uint32_t pred1 = Predictor1(data[x - 1], NULL);
+      AddPixelsEq(data + x, pred1);
+    }
+    data += width;
+    ++y_start;
+  }
+
+  {
+    int y = y_start;
+    const int mask = (1 << transform->bits_) - 1;
+    const int tiles_per_row = VP8LSubSampleSize(width, transform->bits_);
+    const uint32_t* pred_mode_base =
+        transform->data_ + (y >> transform->bits_) * tiles_per_row;
+
+    while (y < y_end) {
+      int x;
+      const uint32_t pred2 = Predictor2(data[-1], data - width);
+      const uint32_t* pred_mode_src = pred_mode_base;
+      PredictorFunc pred_func;
+
+      // First pixel follows the T (mode=2) mode.
+      AddPixelsEq(data, pred2);
+
+      // .. the rest:
+      pred_func = kPredictors[((*pred_mode_src++) >> 8) & 0xf];
+      for (x = 1; x < width; ++x) {
+        uint32_t pred;
+        if ((x & mask) == 0) {    // start of tile. Read predictor function.
+          pred_func = kPredictors[((*pred_mode_src++) >> 8) & 0xf];
+        }
+        pred = pred_func(data[x - 1], data + x - width);
+        AddPixelsEq(data + x, pred);
+      }
+      data += width;
+      ++y;
+      if ((y & mask) == 0) {   // Use the same mask, since tiles are squares.
+        pred_mode_base += tiles_per_row;
+      }
+    }
+  }
+}
+
+void VP8LSubtractGreenFromBlueAndRed(uint32_t* argb_data, int num_pixs) {
+  int i;
+  for (i = 0; i < num_pixs; ++i) {
+    const uint32_t argb = argb_data[i];
+    const uint32_t green = (argb >> 8) & 0xff;
+    const uint32_t new_r = (((argb >> 16) & 0xff) - green) & 0xff;
+    const uint32_t new_b = ((argb & 0xff) - green) & 0xff;
+    argb_data[i] = (argb & 0xff00ff00) | (new_r << 16) | new_b;
+  }
+}
+
+// Add green to blue and red channels (i.e. perform the inverse transform of
+// 'subtract green').
+static void AddGreenToBlueAndRed(const VP8LTransform* const transform,
+                                 int y_start, int y_end, uint32_t* data) {
+  const int width = transform->xsize_;
+  const uint32_t* const data_end = data + (y_end - y_start) * width;
+  while (data < data_end) {
+    const uint32_t argb = *data;
+    // "* 0001001u" is equivalent to "(green << 16) + green)"
+    const uint32_t green = ((argb >> 8) & 0xff);
+    uint32_t red_blue = (argb & 0x00ff00ffu);
+    red_blue += (green << 16) | green;
+    red_blue &= 0x00ff00ffu;
+    *data++ = (argb & 0xff00ff00u) | red_blue;
+  }
+}
+
+typedef struct {
+  // Note: the members are uint8_t, so that any negative values are
+  // automatically converted to "mod 256" values.
+  uint8_t green_to_red_;
+  uint8_t green_to_blue_;
+  uint8_t red_to_blue_;
+} Multipliers;
+
+static WEBP_INLINE void MultipliersClear(Multipliers* m) {
+  m->green_to_red_ = 0;
+  m->green_to_blue_ = 0;
+  m->red_to_blue_ = 0;
+}
+
+static WEBP_INLINE uint32_t ColorTransformDelta(int8_t color_pred,
+                                                int8_t color) {
+  return (uint32_t)((int)(color_pred) * color) >> 5;
+}
+
+static WEBP_INLINE void ColorCodeToMultipliers(uint32_t color_code,
+                                               Multipliers* const m) {
+  m->green_to_red_  = (color_code >>  0) & 0xff;
+  m->green_to_blue_ = (color_code >>  8) & 0xff;
+  m->red_to_blue_   = (color_code >> 16) & 0xff;
+}
+
+static WEBP_INLINE uint32_t MultipliersToColorCode(Multipliers* const m) {
+  return 0xff000000u |
+         ((uint32_t)(m->red_to_blue_) << 16) |
+         ((uint32_t)(m->green_to_blue_) << 8) |
+         m->green_to_red_;
+}
+
+static WEBP_INLINE uint32_t TransformColor(const Multipliers* const m,
+                                           uint32_t argb, int inverse) {
+  const uint32_t green = argb >> 8;
+  const uint32_t red = argb >> 16;
+  uint32_t new_red = red;
+  uint32_t new_blue = argb;
+
+  if (inverse) {
+    new_red += ColorTransformDelta(m->green_to_red_, green);
+    new_red &= 0xff;
+    new_blue += ColorTransformDelta(m->green_to_blue_, green);
+    new_blue += ColorTransformDelta(m->red_to_blue_, new_red);
+    new_blue &= 0xff;
+  } else {
+    new_red -= ColorTransformDelta(m->green_to_red_, green);
+    new_red &= 0xff;
+    new_blue -= ColorTransformDelta(m->green_to_blue_, green);
+    new_blue -= ColorTransformDelta(m->red_to_blue_, red);
+    new_blue &= 0xff;
+  }
+  return (argb & 0xff00ff00u) | (new_red << 16) | (new_blue);
+}
+
+static WEBP_INLINE int SkipRepeatedPixels(const uint32_t* const argb,
+                                          int ix, int xsize) {
+  const uint32_t v = argb[ix];
+  if (ix >= xsize + 3) {
+    if (v == argb[ix - xsize] &&
+        argb[ix - 1] == argb[ix - xsize - 1] &&
+        argb[ix - 2] == argb[ix - xsize - 2] &&
+        argb[ix - 3] == argb[ix - xsize - 3]) {
+      return 1;
+    }
+    return v == argb[ix - 3] && v == argb[ix - 2] && v == argb[ix - 1];
+  } else if (ix >= 3) {
+    return v == argb[ix - 3] && v == argb[ix - 2] && v == argb[ix - 1];
+  }
+  return 0;
+}
+
+static float PredictionCostCrossColor(const int accumulated[256],
+                                      const int counts[256]) {
+  // Favor low entropy, locally and globally.
+  int i;
+  int combo[256];
+  for (i = 0; i < 256; ++i) {
+    combo[i] = accumulated[i] + counts[i];
+  }
+  return ShannonEntropy(combo, 256) +
+         ShannonEntropy(counts, 256) +
+         PredictionCostSpatial(counts, 3, 2.4);  // Favor small absolute values.
+}
+
+static Multipliers GetBestColorTransformForTile(
+    int tile_x, int tile_y, int bits,
+    Multipliers prevX,
+    Multipliers prevY,
+    int step, int xsize, int ysize,
+    int* accumulated_red_histo,
+    int* accumulated_blue_histo,
+    const uint32_t* const argb) {
+  float best_diff = MAX_DIFF_COST;
+  float cur_diff;
+  const int halfstep = step / 2;
+  const int max_tile_size = 1 << bits;
+  const int tile_y_offset = tile_y * max_tile_size;
+  const int tile_x_offset = tile_x * max_tile_size;
+  int green_to_red;
+  int green_to_blue;
+  int red_to_blue;
+  int all_x_max = tile_x_offset + max_tile_size;
+  int all_y_max = tile_y_offset + max_tile_size;
+  Multipliers best_tx;
+  MultipliersClear(&best_tx);
+  if (all_x_max > xsize) {
+    all_x_max = xsize;
+  }
+  if (all_y_max > ysize) {
+    all_y_max = ysize;
+  }
+  for (green_to_red = -64; green_to_red <= 64; green_to_red += halfstep) {
+    int histo[256] = { 0 };
+    int all_y;
+    Multipliers tx;
+    MultipliersClear(&tx);
+    tx.green_to_red_ = green_to_red & 0xff;
+
+    for (all_y = tile_y_offset; all_y < all_y_max; ++all_y) {
+      uint32_t predict;
+      int ix = all_y * xsize + tile_x_offset;
+      int all_x;
+      for (all_x = tile_x_offset; all_x < all_x_max; ++all_x, ++ix) {
+        if (SkipRepeatedPixels(argb, ix, xsize)) {
+          continue;
+        }
+        predict = TransformColor(&tx, argb[ix], 0);
+        ++histo[(predict >> 16) & 0xff];  // red.
+      }
+    }
+    cur_diff = PredictionCostCrossColor(&accumulated_red_histo[0], &histo[0]);
+    if (tx.green_to_red_ == prevX.green_to_red_) {
+      cur_diff -= 3;  // favor keeping the areas locally similar
+    }
+    if (tx.green_to_red_ == prevY.green_to_red_) {
+      cur_diff -= 3;  // favor keeping the areas locally similar
+    }
+    if (tx.green_to_red_ == 0) {
+      cur_diff -= 3;
+    }
+    if (cur_diff < best_diff) {
+      best_diff = cur_diff;
+      best_tx = tx;
+    }
+  }
+  best_diff = MAX_DIFF_COST;
+  green_to_red = best_tx.green_to_red_;
+  for (green_to_blue = -32; green_to_blue <= 32; green_to_blue += step) {
+    for (red_to_blue = -32; red_to_blue <= 32; red_to_blue += step) {
+      int all_y;
+      int histo[256] = { 0 };
+      Multipliers tx;
+      tx.green_to_red_ = green_to_red;
+      tx.green_to_blue_ = green_to_blue;
+      tx.red_to_blue_ = red_to_blue;
+      for (all_y = tile_y_offset; all_y < all_y_max; ++all_y) {
+        uint32_t predict;
+        int all_x;
+        int ix = all_y * xsize + tile_x_offset;
+        for (all_x = tile_x_offset; all_x < all_x_max; ++all_x, ++ix) {
+          if (SkipRepeatedPixels(argb, ix, xsize)) {
+            continue;
+          }
+          predict = TransformColor(&tx, argb[ix], 0);
+          ++histo[predict & 0xff];  // blue.
+        }
+      }
+      cur_diff =
+        PredictionCostCrossColor(&accumulated_blue_histo[0], &histo[0]);
+      if (tx.green_to_blue_ == prevX.green_to_blue_) {
+        cur_diff -= 3;  // favor keeping the areas locally similar
+      }
+      if (tx.green_to_blue_ == prevY.green_to_blue_) {
+        cur_diff -= 3;  // favor keeping the areas locally similar
+      }
+      if (tx.red_to_blue_ == prevX.red_to_blue_) {
+        cur_diff -= 3;  // favor keeping the areas locally similar
+      }
+      if (tx.red_to_blue_ == prevY.red_to_blue_) {
+        cur_diff -= 3;  // favor keeping the areas locally similar
+      }
+      if (tx.green_to_blue_ == 0) {
+        cur_diff -= 3;
+      }
+      if (tx.red_to_blue_ == 0) {
+        cur_diff -= 3;
+      }
+      if (cur_diff < best_diff) {
+        best_diff = cur_diff;
+        best_tx = tx;
+      }
+    }
+  }
+  return best_tx;
+}
+
+static void CopyTileWithColorTransform(int xsize, int ysize,
+                                       int tile_x, int tile_y, int bits,
+                                       Multipliers color_transform,
+                                       uint32_t* const argb) {
+  int y;
+  int xscan = 1 << bits;
+  int yscan = 1 << bits;
+  tile_x <<= bits;
+  tile_y <<= bits;
+  if (xscan > xsize - tile_x) {
+    xscan = xsize - tile_x;
+  }
+  if (yscan > ysize - tile_y) {
+    yscan = ysize - tile_y;
+  }
+  yscan += tile_y;
+  for (y = tile_y; y < yscan; ++y) {
+    int ix = y * xsize + tile_x;
+    const int end_ix = ix + xscan;
+    for (; ix < end_ix; ++ix) {
+      argb[ix] = TransformColor(&color_transform, argb[ix], 0);
+    }
+  }
+}
+
+void VP8LColorSpaceTransform(int width, int height, int bits, int step,
+                             uint32_t* const argb, uint32_t* image) {
+  const int max_tile_size = 1 << bits;
+  int tile_xsize = VP8LSubSampleSize(width, bits);
+  int tile_ysize = VP8LSubSampleSize(height, bits);
+  int accumulated_red_histo[256] = { 0 };
+  int accumulated_blue_histo[256] = { 0 };
+  int tile_y;
+  int tile_x;
+  Multipliers prevX;
+  Multipliers prevY;
+  MultipliersClear(&prevY);
+  MultipliersClear(&prevX);
+  for (tile_y = 0; tile_y < tile_ysize; ++tile_y) {
+    for (tile_x = 0; tile_x < tile_xsize; ++tile_x) {
+      Multipliers color_transform;
+      int all_x_max;
+      int y;
+      const int tile_y_offset = tile_y * max_tile_size;
+      const int tile_x_offset = tile_x * max_tile_size;
+      if (tile_y != 0) {
+        ColorCodeToMultipliers(image[tile_y * tile_xsize + tile_x - 1], &prevX);
+        ColorCodeToMultipliers(image[(tile_y - 1) * tile_xsize + tile_x],
+                               &prevY);
+      } else if (tile_x != 0) {
+        ColorCodeToMultipliers(image[tile_y * tile_xsize + tile_x - 1], &prevX);
+      }
+      color_transform =
+          GetBestColorTransformForTile(tile_x, tile_y, bits,
+                                       prevX, prevY,
+                                       step, width, height,
+                                       &accumulated_red_histo[0],
+                                       &accumulated_blue_histo[0],
+                                       argb);
+      image[tile_y * tile_xsize + tile_x] =
+          MultipliersToColorCode(&color_transform);
+      CopyTileWithColorTransform(width, height, tile_x, tile_y, bits,
+                                 color_transform, argb);
+
+      // Gather accumulated histogram data.
+      all_x_max = tile_x_offset + max_tile_size;
+      if (all_x_max > width) {
+        all_x_max = width;
+      }
+      for (y = 0; y < max_tile_size; ++y) {
+        int ix;
+        int all_x;
+        int all_y = tile_y_offset + y;
+        if (all_y >= height) {
+          break;
+        }
+        ix = all_y * width + tile_x_offset;
+        for (all_x = tile_x_offset; all_x < all_x_max; ++all_x, ++ix) {
+          if (ix >= 2 &&
+              argb[ix] == argb[ix - 2] &&
+              argb[ix] == argb[ix - 1]) {
+            continue;  // repeated pixels are handled by backward references
+          }
+          if (ix >= width + 2 &&
+              argb[ix - 2] == argb[ix - width - 2] &&
+              argb[ix - 1] == argb[ix - width - 1] &&
+              argb[ix] == argb[ix - width]) {
+            continue;  // repeated pixels are handled by backward references
+          }
+          ++accumulated_red_histo[(argb[ix] >> 16) & 0xff];
+          ++accumulated_blue_histo[argb[ix] & 0xff];
+        }
+      }
+    }
+  }
+}
+
+// Color space inverse transform.
+static void ColorSpaceInverseTransform(const VP8LTransform* const transform,
+                                       int y_start, int y_end, uint32_t* data) {
+  const int width = transform->xsize_;
+  const int mask = (1 << transform->bits_) - 1;
+  const int tiles_per_row = VP8LSubSampleSize(width, transform->bits_);
+  int y = y_start;
+  const uint32_t* pred_row =
+      transform->data_ + (y >> transform->bits_) * tiles_per_row;
+
+  while (y < y_end) {
+    const uint32_t* pred = pred_row;
+    Multipliers m = { 0, 0, 0 };
+    int x;
+
+    for (x = 0; x < width; ++x) {
+      if ((x & mask) == 0) ColorCodeToMultipliers(*pred++, &m);
+      data[x] = TransformColor(&m, data[x], 1);
+    }
+    data += width;
+    ++y;
+    if ((y & mask) == 0) pred_row += tiles_per_row;;
+  }
+}
+
+// Separate out pixels packed together using pixel-bundling.
+static void ColorIndexInverseTransform(
+    const VP8LTransform* const transform,
+    int y_start, int y_end, const uint32_t* src, uint32_t* dst) {
+  int y;
+  const int bits_per_pixel = 8 >> transform->bits_;
+  const int width = transform->xsize_;
+  const uint32_t* const color_map = transform->data_;
+  if (bits_per_pixel < 8) {
+    const int pixels_per_byte = 1 << transform->bits_;
+    const int count_mask = pixels_per_byte - 1;
+    const uint32_t bit_mask = (1 << bits_per_pixel) - 1;
+    for (y = y_start; y < y_end; ++y) {
+      uint32_t packed_pixels = 0;
+      int x;
+      for (x = 0; x < width; ++x) {
+        // We need to load fresh 'packed_pixels' once every 'bytes_per_pixels'
+        // increments of x. Fortunately, pixels_per_byte is a power of 2, so
+        // can just use a mask for that, instead of decrementing a counter.
+        if ((x & count_mask) == 0) packed_pixels = ((*src++) >> 8) & 0xff;
+        *dst++ = color_map[packed_pixels & bit_mask];
+        packed_pixels >>= bits_per_pixel;
+      }
+    }
+  } else {
+    for (y = y_start; y < y_end; ++y) {
+      int x;
+      for (x = 0; x < width; ++x) {
+        *dst++ = color_map[((*src++) >> 8) & 0xff];
+      }
+    }
+  }
+}
+
+void VP8LInverseTransform(const VP8LTransform* const transform,
+                          int row_start, int row_end,
+                          const uint32_t* const in, uint32_t* const out) {
+  assert(row_start < row_end);
+  assert(row_end <= transform->ysize_);
+  switch (transform->type_) {
+    case SUBTRACT_GREEN:
+      AddGreenToBlueAndRed(transform, row_start, row_end, out);
+      break;
+    case PREDICTOR_TRANSFORM:
+      PredictorInverseTransform(transform, row_start, row_end, out);
+      if (row_end != transform->ysize_) {
+        // The last predicted row in this iteration will be the top-pred row
+        // for the first row in next iteration.
+        const int width = transform->xsize_;
+        memcpy(out - width, out + (row_end - row_start - 1) * width,
+               width * sizeof(*out));
+      }
+      break;
+    case CROSS_COLOR_TRANSFORM:
+      ColorSpaceInverseTransform(transform, row_start, row_end, out);
+      break;
+    case COLOR_INDEXING_TRANSFORM:
+      ColorIndexInverseTransform(transform, row_start, row_end, in, out);
+      break;
+  }
+}
+
+//------------------------------------------------------------------------------
+// Color space conversion.
+
+static int is_big_endian(void) {
+  static const union {
+    uint16_t w;
+    uint8_t b[2];
+  } tmp = { 1 };
+  return (tmp.b[0] != 1);
+}
+
+static void ConvertBGRAToRGB(const uint32_t* src,
+                             int num_pixels, uint8_t* dst) {
+  const uint32_t* const src_end = src + num_pixels;
+  while (src < src_end) {
+    const uint32_t argb = *src++;
+    *dst++ = (argb >> 16) & 0xff;
+    *dst++ = (argb >>  8) & 0xff;
+    *dst++ = (argb >>  0) & 0xff;
+  }
+}
+
+static void ConvertBGRAToRGBA(const uint32_t* src,
+                              int num_pixels, uint8_t* dst) {
+  const uint32_t* const src_end = src + num_pixels;
+  while (src < src_end) {
+    const uint32_t argb = *src++;
+    *dst++ = (argb >> 16) & 0xff;
+    *dst++ = (argb >>  8) & 0xff;
+    *dst++ = (argb >>  0) & 0xff;
+    *dst++ = (argb >> 24) & 0xff;
+  }
+}
+
+static void ConvertBGRAToRGBA4444(const uint32_t* src,
+                                  int num_pixels, uint8_t* dst) {
+  const uint32_t* const src_end = src + num_pixels;
+  while (src < src_end) {
+    const uint32_t argb = *src++;
+    *dst++ = ((argb >> 16) & 0xf0) | ((argb >> 12) & 0xf);
+    *dst++ = ((argb >>  0) & 0xf0) | ((argb >> 28) & 0xf);
+  }
+}
+
+static void ConvertBGRAToRGB565(const uint32_t* src,
+                                int num_pixels, uint8_t* dst) {
+  const uint32_t* const src_end = src + num_pixels;
+  while (src < src_end) {
+    const uint32_t argb = *src++;
+    *dst++ = ((argb >> 16) & 0xf8) | ((argb >> 13) & 0x7);
+    *dst++ = ((argb >>  5) & 0xe0) | ((argb >>  3) & 0x1f);
+  }
+}
+
+static void ConvertBGRAToBGR(const uint32_t* src,
+                             int num_pixels, uint8_t* dst) {
+  const uint32_t* const src_end = src + num_pixels;
+  while (src < src_end) {
+    const uint32_t argb = *src++;
+    *dst++ = (argb >>  0) & 0xff;
+    *dst++ = (argb >>  8) & 0xff;
+    *dst++ = (argb >> 16) & 0xff;
+  }
+}
+
+static void CopyOrSwap(const uint32_t* src, int num_pixels, uint8_t* dst,
+                       int swap_on_big_endian) {
+  if (is_big_endian() == swap_on_big_endian) {
+    const uint32_t* const src_end = src + num_pixels;
+    while (src < src_end) {
+      uint32_t argb = *src++;
+#if !defined(__BIG_ENDIAN__) && (defined(__i386__) || defined(__x86_64__))
+      __asm__ volatile("bswap %0" : "=r"(argb) : "0"(argb));
+      *(uint32_t*)dst = argb;
+      dst += sizeof(argb);
+#elif !defined(__BIG_ENDIAN__) && defined(_MSC_VER)
+      argb = _byteswap_ulong(argb);
+      *(uint32_t*)dst = argb;
+      dst += sizeof(argb);
+#else
+      *dst++ = (argb >> 24) & 0xff;
+      *dst++ = (argb >> 16) & 0xff;
+      *dst++ = (argb >>  8) & 0xff;
+      *dst++ = (argb >>  0) & 0xff;
+#endif
+    }
+  } else {
+    memcpy(dst, src, num_pixels * sizeof(*src));
+  }
+}
+
+void VP8LConvertFromBGRA(const uint32_t* const in_data, int num_pixels,
+                         WEBP_CSP_MODE out_colorspace, uint8_t* const rgba) {
+  switch (out_colorspace) {
+    case MODE_RGB:
+      ConvertBGRAToRGB(in_data, num_pixels, rgba);
+      break;
+    case MODE_RGBA:
+      ConvertBGRAToRGBA(in_data, num_pixels, rgba);
+      break;
+    case MODE_rgbA:
+      ConvertBGRAToRGBA(in_data, num_pixels, rgba);
+      WebPApplyAlphaMultiply(rgba, 0, num_pixels, 1, 0);
+      break;
+    case MODE_BGR:
+      ConvertBGRAToBGR(in_data, num_pixels, rgba);
+      break;
+    case MODE_BGRA:
+      CopyOrSwap(in_data, num_pixels, rgba, 1);
+      break;
+    case MODE_bgrA:
+      CopyOrSwap(in_data, num_pixels, rgba, 1);
+      WebPApplyAlphaMultiply(rgba, 0, num_pixels, 1, 0);
+      break;
+    case MODE_ARGB:
+      CopyOrSwap(in_data, num_pixels, rgba, 0);
+      break;
+    case MODE_Argb:
+      CopyOrSwap(in_data, num_pixels, rgba, 0);
+      WebPApplyAlphaMultiply(rgba, 1, num_pixels, 1, 0);
+      break;
+    case MODE_RGBA_4444:
+      ConvertBGRAToRGBA4444(in_data, num_pixels, rgba);
+      break;
+    case MODE_rgbA_4444:
+      ConvertBGRAToRGBA4444(in_data, num_pixels, rgba);
+      WebPApplyAlphaMultiply4444(rgba, num_pixels, 1, 0);
+      break;
+    case MODE_RGB_565:
+      ConvertBGRAToRGB565(in_data, num_pixels, rgba);
+      break;
+    default:
+      assert(0);          // Code flow should not reach here.
+  }
+}
+
+//------------------------------------------------------------------------------
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}    // extern "C"
+#endif