libwebp/src/dsp/lossless.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.
// -----------------------------------------------------------------------------
//
// 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)

#include "./dsp.h"

#include <math.h>
#include <stdlib.h>
#include "../dec/vp8li.h"
#include "../utils/endian_inl.h"
#include "./lossless.h"
#include "./yuv.h"

#define MAX_DIFF_COST (1e30f)

// lookup table for small values of log2(int)
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
};

const float kSLog2Table[LOG_LOOKUP_IDX_MAX] = {
  0.00000000f,    0.00000000f,  2.00000000f,   4.75488750f,
  8.00000000f,   11.60964047f,  15.50977500f,  19.65148445f,
  24.00000000f,  28.52932501f,  33.21928095f,  38.05374781f,
  43.01955001f,  48.10571634f,  53.30296891f,  58.60335893f,
  64.00000000f,  69.48686830f,  75.05865003f,  80.71062276f,
  86.43856190f,  92.23866588f,  98.10749561f,  104.04192499f,
  110.03910002f, 116.09640474f, 122.21143267f, 128.38196256f,
  134.60593782f, 140.88144886f, 147.20671787f, 153.58008562f,
  160.00000000f, 166.46500594f, 172.97373660f, 179.52490559f,
  186.11730005f, 192.74977453f, 199.42124551f, 206.13068654f,
  212.87712380f, 219.65963219f, 226.47733176f, 233.32938445f,
  240.21499122f, 247.13338933f, 254.08384998f, 261.06567603f,
  268.07820003f, 275.12078236f, 282.19280949f, 289.29369244f,
  296.42286534f, 303.57978409f, 310.76392512f, 317.97478424f,
  325.21187564f, 332.47473081f, 339.76289772f, 347.07593991f,
  354.41343574f, 361.77497759f, 369.16017124f, 376.56863518f,
  384.00000000f, 391.45390785f, 398.93001188f, 406.42797576f,
  413.94747321f, 421.48818752f, 429.04981119f, 436.63204548f,
  444.23460010f, 451.85719280f, 459.49954906f, 467.16140179f,
  474.84249102f, 482.54256363f, 490.26137307f, 497.99867911f,
  505.75424759f, 513.52785023f, 521.31926438f, 529.12827280f,
  536.95466351f, 544.79822957f, 552.65876890f, 560.53608414f,
  568.42998244f, 576.34027536f, 584.26677867f, 592.20931226f,
  600.16769996f, 608.14176943f, 616.13135206f, 624.13628279f,
  632.15640007f, 640.19154569f, 648.24156472f, 656.30630539f,
  664.38561898f, 672.47935976f, 680.58738488f, 688.70955430f,
  696.84573069f, 704.99577935f, 713.15956818f, 721.33696754f,
  729.52785023f, 737.73209140f, 745.94956849f, 754.18016116f,
  762.42375127f, 770.68022275f, 778.94946161f, 787.23135586f,
  795.52579543f, 803.83267219f, 812.15187982f, 820.48331383f,
  828.82687147f, 837.18245171f, 845.54995518f, 853.92928416f,
  862.32034249f, 870.72303558f, 879.13727036f, 887.56295522f,
  896.00000000f, 904.44831595f, 912.90781569f, 921.37841320f,
  929.86002376f, 938.35256392f, 946.85595152f, 955.37010560f,
  963.89494641f, 972.43039537f, 980.97637504f, 989.53280911f,
  998.09962237f, 1006.67674069f, 1015.26409097f, 1023.86160116f,
  1032.46920021f, 1041.08681805f, 1049.71438560f, 1058.35183469f,
  1066.99909811f, 1075.65610955f, 1084.32280357f, 1092.99911564f,
  1101.68498204f, 1110.38033993f, 1119.08512727f, 1127.79928282f,
  1136.52274614f, 1145.25545758f, 1153.99735821f, 1162.74838989f,
  1171.50849518f, 1180.27761738f, 1189.05570047f, 1197.84268914f,
  1206.63852876f, 1215.44316535f, 1224.25654560f, 1233.07861684f,
  1241.90932703f, 1250.74862473f, 1259.59645914f, 1268.45278005f,
  1277.31753781f, 1286.19068338f, 1295.07216828f, 1303.96194457f,
  1312.85996488f, 1321.76618236f, 1330.68055071f, 1339.60302413f,
  1348.53355734f, 1357.47210556f, 1366.41862452f, 1375.37307041f,
  1384.33539991f, 1393.30557020f, 1402.28353887f, 1411.26926400f,
  1420.26270412f, 1429.26381818f, 1438.27256558f, 1447.28890615f,
  1456.31280014f, 1465.34420819f, 1474.38309138f, 1483.42941118f,
  1492.48312945f, 1501.54420843f, 1510.61261078f, 1519.68829949f,
  1528.77123795f, 1537.86138993f, 1546.95871952f, 1556.06319119f,
  1565.17476976f, 1574.29342040f, 1583.41910860f, 1592.55180020f,
  1601.69146137f, 1610.83805860f, 1619.99155871f, 1629.15192882f,
  1638.31913637f, 1647.49314911f, 1656.67393509f, 1665.86146266f,
  1675.05570047f, 1684.25661744f, 1693.46418280f, 1702.67836605f,
  1711.89913698f, 1721.12646563f, 1730.36032233f, 1739.60067768f,
  1748.84750254f, 1758.10076802f, 1767.36044551f, 1776.62650662f,
  1785.89892323f, 1795.17766747f, 1804.46271172f, 1813.75402857f,
  1823.05159087f, 1832.35537170f, 1841.66534438f, 1850.98148244f,
  1860.30375965f, 1869.63214999f, 1878.96662767f, 1888.30716711f,
  1897.65374295f, 1907.00633003f, 1916.36490342f, 1925.72943838f,
  1935.09991037f, 1944.47629506f, 1953.85856831f, 1963.24670620f,
  1972.64068498f, 1982.04048108f, 1991.44607117f, 2000.85743204f,
  2010.27454072f, 2019.69737440f, 2029.12591044f, 2038.56012640f
};

const VP8LPrefixCode kPrefixEncodeCode[PREFIX_LOOKUP_IDX_MAX] = {
  { 0, 0}, { 0, 0}, { 1, 0}, { 2, 0}, { 3, 0}, { 4, 1}, { 4, 1}, { 5, 1},
  { 5, 1}, { 6, 2}, { 6, 2}, { 6, 2}, { 6, 2}, { 7, 2}, { 7, 2}, { 7, 2},
  { 7, 2}, { 8, 3}, { 8, 3}, { 8, 3}, { 8, 3}, { 8, 3}, { 8, 3}, { 8, 3},
  { 8, 3}, { 9, 3}, { 9, 3}, { 9, 3}, { 9, 3}, { 9, 3}, { 9, 3}, { 9, 3},
  { 9, 3}, {10, 4}, {10, 4}, {10, 4}, {10, 4}, {10, 4}, {10, 4}, {10, 4},
  {10, 4}, {10, 4}, {10, 4}, {10, 4}, {10, 4}, {10, 4}, {10, 4}, {10, 4},
  {10, 4}, {11, 4}, {11, 4}, {11, 4}, {11, 4}, {11, 4}, {11, 4}, {11, 4},
  {11, 4}, {11, 4}, {11, 4}, {11, 4}, {11, 4}, {11, 4}, {11, 4}, {11, 4},
  {11, 4}, {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5},
  {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5},
  {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5},
  {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5}, {12, 5},
  {12, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5},
  {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5},
  {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5},
  {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5}, {13, 5},
  {13, 5}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6},
  {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6},
  {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6},
  {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6},
  {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6},
  {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6},
  {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6},
  {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6}, {14, 6},
  {14, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6},
  {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6},
  {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6},
  {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6},
  {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6},
  {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6},
  {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6},
  {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6}, {15, 6},
  {15, 6}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7}, {16, 7},
  {16, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
  {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7}, {17, 7},
};

const uint8_t kPrefixEncodeExtraBitsValue[PREFIX_LOOKUP_IDX_MAX] = {
   0,  0,  0,  0,  0,  0,  1,  0,  1,  0,  1,  2,  3,  0,  1,  2,  3,
   0,  1,  2,  3,  4,  5,  6,  7,  0,  1,  2,  3,  4,  5,  6,  7,
   0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
   0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
   0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
  16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
   0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
  16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
   0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
  16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
  32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
  48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
   0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
  16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
  32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
  48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
   0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
  16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
  32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
  48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
  64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
  80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95,
  96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111,
  112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126,
  127,
   0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
  16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
  32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
  48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
  64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
  80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95,
  96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111,
  112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126
};

// The threshold till approximate version of log_2 can be used.
// Practically, we can get rid of the call to log() as the two values match to
// very high degree (the ratio of these two is 0.99999x).
// Keeping a high threshold for now.
#define APPROX_LOG_WITH_CORRECTION_MAX  65536
#define APPROX_LOG_MAX                   4096
#define LOG_2_RECIPROCAL 1.44269504088896338700465094007086
static float FastSLog2Slow(uint32_t v) {
  assert(v >= LOG_LOOKUP_IDX_MAX);
  if (v < APPROX_LOG_WITH_CORRECTION_MAX) {
    int log_cnt = 0;
    uint32_t y = 1;
    int correction = 0;
    const float v_f = (float)v;
    const uint32_t orig_v = v;
    do {
      ++log_cnt;
      v = v >> 1;
      y = y << 1;
    } while (v >= LOG_LOOKUP_IDX_MAX);
    // vf = (2^log_cnt) * Xf; where y = 2^log_cnt and Xf < 256
    // Xf = floor(Xf) * (1 + (v % y) / v)
    // log2(Xf) = log2(floor(Xf)) + log2(1 + (v % y) / v)
    // The correction factor: log(1 + d) ~ d; for very small d values, so
    // log2(1 + (v % y) / v) ~ LOG_2_RECIPROCAL * (v % y)/v
    // LOG_2_RECIPROCAL ~ 23/16
    correction = (23 * (orig_v & (y - 1))) >> 4;
    return v_f * (kLog2Table[v] + log_cnt) + correction;
  } else {
    return (float)(LOG_2_RECIPROCAL * v * log((double)v));
  }
}

static float FastLog2Slow(uint32_t v) {
  assert(v >= LOG_LOOKUP_IDX_MAX);
  if (v < APPROX_LOG_WITH_CORRECTION_MAX) {
    int log_cnt = 0;
    uint32_t y = 1;
    const uint32_t orig_v = v;
    double log_2;
    do {
      ++log_cnt;
      v = v >> 1;
      y = y << 1;
    } while (v >= LOG_LOOKUP_IDX_MAX);
    log_2 = kLog2Table[v] + log_cnt;
    if (orig_v >= APPROX_LOG_MAX) {
      // Since the division is still expensive, add this correction factor only
      // for large values of 'v'.
      const int correction = (23 * (orig_v & (y - 1))) >> 4;
      log_2 += (double)correction / orig_v;
    }
    return (float)log_2;
  } else {
    return (float)(LOG_2_RECIPROCAL * log((double)v));
  }
}

//------------------------------------------------------------------------------
// Image transforms.

// Mostly used to reduce code size + readability
static WEBP_INLINE int GetMin(int a, int b) { return (a > b) ? b : a; }

// 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 ((uint32_t)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 ((uint32_t)a << 24) | (r << 16) | (g << 8) | b;
}

static WEBP_INLINE int Sub3(int a, int b, int c) {
  const int pb = b - c;
  const int pa = a - c;
  return abs(pb) - abs(pa);
}

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;
}

static const VP8LPredictorFunc kPredictorsC[16] = {
  Predictor0, Predictor1, Predictor2, Predictor3,
  Predictor4, Predictor5, Predictor6, Predictor7,
  Predictor8, Predictor9, Predictor10, Predictor11,
  Predictor12, Predictor13,
  Predictor0, Predictor0    // <- padding security sentinels
};

static float PredictionCostSpatial(const int counts[256], int weight_0,
                                   double exp_val) {
  const int significant_symbols = 256 >> 4;
  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 combined Shanon's entropy for distribution {X} and {X+Y}
static float CombinedShannonEntropy(const int X[256], const int Y[256]) {
  int i;
  double retval = 0.;
  int sumX = 0, sumXY = 0;
  for (i = 0; i < 256; ++i) {
    const int x = X[i];
    const int xy = x + Y[i];
    if (x != 0) {
      sumX += x;
      retval -= VP8LFastSLog2(x);
      sumXY += xy;
      retval -= VP8LFastSLog2(xy);
    } else if (xy != 0) {
      sumXY += xy;
      retval -= VP8LFastSLog2(xy);
    }
  }
  retval += VP8LFastSLog2(sumX) + VP8LFastSLog2(sumXY);
  return (float)retval;
}

static float PredictionCostSpatialHistogram(const int accumulated[4][256],
                                            const int tile[4][256]) {
  int i;
  double retval = 0;
  for (i = 0; i < 4; ++i) {
    const double kExpValue = 0.94;
    retval += PredictionCostSpatial(tile[i], 1, kExpValue);
    retval += CombinedShannonEntropy(tile[i], accumulated[i]);
  }
  return (float)retval;
}

static WEBP_INLINE void UpdateHisto(int histo_argb[4][256], uint32_t argb) {
  ++histo_argb[0][argb >> 24];
  ++histo_argb[1][(argb >> 16) & 0xff];
  ++histo_argb[2][(argb >> 8) & 0xff];
  ++histo_argb[3][argb & 0xff];
}

static int GetBestPredictorForTile(int width, int height,
                                   int tile_x, int tile_y, int bits,
                                   const 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 max_y = GetMin(tile_size, height - row_start);
  const int max_x = GetMin(tile_size, width - col_start);
  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 VP8LPredictorFunc pred_func = VP8LPredictors[mode];
    float cur_diff;
    int y;
    int histo_argb[4][256];
    memset(histo_argb, 0, sizeof(histo_argb));
    for (y = 0; y < max_y; ++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 < max_x; ++x) {
        const int col = col_start + x;
        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);
        }
        UpdateHisto(histo_argb, VP8LSubPixels(current_row[col], predict));
      }
    }
    cur_diff = PredictionCostSpatialHistogram(
        accumulated, (const int (*)[256])histo_argb);
    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 max_y = GetMin(tile_size, height - row_start);
  const int max_x = GetMin(tile_size, width - col_start);
  const VP8LPredictorFunc pred_func = VP8LPredictors[mode];
  const uint32_t* current_row = argb_scratch;

  int y;
  for (y = 0; y < max_y; ++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 < max_x; ++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,
                                     (const int (*)[256])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) {
          UpdateHisto(histo, argb[ix]);
        }
      }
    }
  }
}

// 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 tile_width = 1 << transform->bits_;
    const int mask = tile_width - 1;
    const int safe_width = width & ~mask;
    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) {
      const uint32_t pred2 = Predictor2(data[-1], data - width);
      const uint32_t* pred_mode_src = pred_mode_base;
      VP8LPredictorFunc pred_func;
      int x = 1;
      int t = 1;
      // First pixel follows the T (mode=2) mode.
      AddPixelsEq(data, pred2);
      // .. the rest:
      while (x < safe_width) {
        pred_func = VP8LPredictors[((*pred_mode_src++) >> 8) & 0xf];
        for (; t < tile_width; ++t, ++x) {
          const uint32_t pred = pred_func(data[x - 1], data + x - width);
          AddPixelsEq(data + x, pred);
        }
        t = 0;
      }
      if (x < width) {
        pred_func = VP8LPredictors[((*pred_mode_src++) >> 8) & 0xf];
        for (; x < width; ++x) {
          const uint32_t 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_C(uint32_t* argb_data, int num_pixels) {
  int i;
  for (i = 0; i < num_pixels; ++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').
void VP8LAddGreenToBlueAndRed_C(uint32_t* data, int num_pixels) {
  int i;
  for (i = 0; i < num_pixels; ++i) {
    const uint32_t argb = data[i];
    const uint32_t green = ((argb >> 8) & 0xff);
    uint32_t red_blue = (argb & 0x00ff00ffu);
    red_blue += (green << 16) | green;
    red_blue &= 0x00ff00ffu;
    data[i] = (argb & 0xff00ff00u) | red_blue;
  }
}

static WEBP_INLINE void MultipliersClear(VP8LMultipliers* const 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,
                                               VP8LMultipliers* 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(
    const VP8LMultipliers* const m) {
  return 0xff000000u |
         ((uint32_t)(m->red_to_blue_) << 16) |
         ((uint32_t)(m->green_to_blue_) << 8) |
         m->green_to_red_;
}

void VP8LTransformColor_C(const VP8LMultipliers* const m, uint32_t* data,
                          int num_pixels) {
  int i;
  for (i = 0; i < num_pixels; ++i) {
    const uint32_t argb = data[i];
    const uint32_t green = argb >> 8;
    const uint32_t red = argb >> 16;
    uint32_t new_red = red;
    uint32_t new_blue = argb;
    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;
    data[i] = (argb & 0xff00ff00u) | (new_red << 16) | (new_blue);
  }
}

void VP8LTransformColorInverse_C(const VP8LMultipliers* const m, uint32_t* data,
                                 int num_pixels) {
  int i;
  for (i = 0; i < num_pixels; ++i) {
    const uint32_t argb = data[i];
    const uint32_t green = argb >> 8;
    const uint32_t red = argb >> 16;
    uint32_t new_red = red;
    uint32_t new_blue = argb;
    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;
    data[i] = (argb & 0xff00ff00u) | (new_red << 16) | (new_blue);
  }
}

static WEBP_INLINE uint8_t TransformColorRed(uint8_t green_to_red,
                                             uint32_t argb) {
  const uint32_t green = argb >> 8;
  uint32_t new_red = argb >> 16;
  new_red -= ColorTransformDelta(green_to_red, green);
  return (new_red & 0xff);
}

static WEBP_INLINE uint8_t TransformColorBlue(uint8_t green_to_blue,
                                              uint8_t red_to_blue,
                                              uint32_t argb) {
  const uint32_t green = argb >> 8;
  const uint32_t red = argb >> 16;
  uint8_t new_blue = argb;
  new_blue -= ColorTransformDelta(green_to_blue, green);
  new_blue -= ColorTransformDelta(red_to_blue, red);
  return (new_blue & 0xff);
}

static float PredictionCostCrossColor(const int accumulated[256],
                                      const int counts[256]) {
  // Favor low entropy, locally and globally.
  // Favor small absolute values for PredictionCostSpatial
  static const double kExpValue = 2.4;
  return CombinedShannonEntropy(counts, accumulated) +
         PredictionCostSpatial(counts, 3, kExpValue);
}

static float GetPredictionCostCrossColorRed(
    int tile_x_offset, int tile_y_offset, int all_x_max, int all_y_max,
    int xsize, VP8LMultipliers prev_x, VP8LMultipliers prev_y, int green_to_red,
    const int accumulated_red_histo[256], const uint32_t* const argb) {
  int all_y;
  int histo[256] = { 0 };
  float cur_diff;
  for (all_y = tile_y_offset; all_y < all_y_max; ++all_y) {
    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) {
      ++histo[TransformColorRed(green_to_red, argb[ix])];  // red.
    }
  }
  cur_diff = PredictionCostCrossColor(accumulated_red_histo, histo);
  if ((uint8_t)green_to_red == prev_x.green_to_red_) {
    cur_diff -= 3;  // favor keeping the areas locally similar
  }
  if ((uint8_t)green_to_red == prev_y.green_to_red_) {
    cur_diff -= 3;  // favor keeping the areas locally similar
  }
  if (green_to_red == 0) {
    cur_diff -= 3;
  }
  return cur_diff;
}

static void GetBestGreenToRed(
    int tile_x_offset, int tile_y_offset, int all_x_max, int all_y_max,
    int xsize, VP8LMultipliers prev_x, VP8LMultipliers prev_y,
    const int accumulated_red_histo[256], const uint32_t* const argb,
    VP8LMultipliers* const best_tx) {
  int min_green_to_red = -64;
  int max_green_to_red = 64;
  int green_to_red = 0;
  int eval_min = 1;
  int eval_max = 1;
  float cur_diff_min = MAX_DIFF_COST;
  float cur_diff_max = MAX_DIFF_COST;
  // Do a binary search to find the optimal green_to_red color transform.
  while (max_green_to_red - min_green_to_red > 2) {
    if (eval_min) {
      cur_diff_min = GetPredictionCostCrossColorRed(
          tile_x_offset, tile_y_offset, all_x_max, all_y_max, xsize,
          prev_x, prev_y, min_green_to_red, accumulated_red_histo, argb);
      eval_min = 0;
    }
    if (eval_max) {
      cur_diff_max = GetPredictionCostCrossColorRed(
          tile_x_offset, tile_y_offset, all_x_max, all_y_max, xsize,
          prev_x, prev_y, max_green_to_red, accumulated_red_histo, argb);
      eval_max = 0;
    }
    if (cur_diff_min < cur_diff_max) {
      green_to_red = min_green_to_red;
      max_green_to_red = (max_green_to_red + min_green_to_red) / 2;
      eval_max = 1;
    } else {
      green_to_red = max_green_to_red;
      min_green_to_red = (max_green_to_red + min_green_to_red) / 2;
      eval_min = 1;
    }
  }
  best_tx->green_to_red_ = green_to_red;
}

static float GetPredictionCostCrossColorBlue(
    int tile_x_offset, int tile_y_offset, int all_x_max, int all_y_max,
    int xsize, VP8LMultipliers prev_x, VP8LMultipliers prev_y,
    int green_to_blue, int red_to_blue, const int accumulated_blue_histo[256],
    const uint32_t* const argb) {
  int all_y;
  int histo[256] = { 0 };
  float cur_diff;
  for (all_y = tile_y_offset; all_y < all_y_max; ++all_y) {
    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) {
      ++histo[TransformColorBlue(green_to_blue, red_to_blue, argb[ix])];
    }
  }
  cur_diff = PredictionCostCrossColor(accumulated_blue_histo, histo);
  if ((uint8_t)green_to_blue == prev_x.green_to_blue_) {
    cur_diff -= 3;  // favor keeping the areas locally similar
  }
  if ((uint8_t)green_to_blue == prev_y.green_to_blue_) {
    cur_diff -= 3;  // favor keeping the areas locally similar
  }
  if ((uint8_t)red_to_blue == prev_x.red_to_blue_) {
    cur_diff -= 3;  // favor keeping the areas locally similar
  }
  if ((uint8_t)red_to_blue == prev_y.red_to_blue_) {
    cur_diff -= 3;  // favor keeping the areas locally similar
  }
  if (green_to_blue == 0) {
    cur_diff -= 3;
  }
  if (red_to_blue == 0) {
    cur_diff -= 3;
  }
  return cur_diff;
}

static void GetBestGreenRedToBlue(
    int tile_x_offset, int tile_y_offset, int all_x_max, int all_y_max,
    int xsize, VP8LMultipliers prev_x, VP8LMultipliers prev_y, int quality,
    const int accumulated_blue_histo[256], const uint32_t* const argb,
    VP8LMultipliers* const best_tx) {
  float best_diff = MAX_DIFF_COST;
  float cur_diff;
  const int step = (quality < 25) ? 32 : (quality > 50) ? 8 : 16;
  const int min_green_to_blue = -32;
  const int max_green_to_blue = 32;
  const int min_red_to_blue = -32;
  const int max_red_to_blue = 32;
  const int num_iters =
      (1 + (max_green_to_blue - min_green_to_blue) / step) *
      (1 + (max_red_to_blue - min_red_to_blue) / step);
  // Number of tries to get optimal green_to_blue & red_to_blue color transforms
  // after finding a local minima.
  const int max_tries_after_min = 4 + (num_iters >> 2);
  int num_tries_after_min = 0;
  int green_to_blue;
  for (green_to_blue = min_green_to_blue;
       green_to_blue <= max_green_to_blue &&
       num_tries_after_min < max_tries_after_min;
       green_to_blue += step) {
    int red_to_blue;
    for (red_to_blue = min_red_to_blue;
         red_to_blue <= max_red_to_blue &&
         num_tries_after_min < max_tries_after_min;
         red_to_blue += step) {
      cur_diff = GetPredictionCostCrossColorBlue(
          tile_x_offset, tile_y_offset, all_x_max, all_y_max, xsize, prev_x,
          prev_y, green_to_blue, red_to_blue, accumulated_blue_histo, argb);
      if (cur_diff < best_diff) {
        best_diff = cur_diff;
        best_tx->green_to_blue_ = green_to_blue;
        best_tx->red_to_blue_ = red_to_blue;
        num_tries_after_min = 0;
      } else {
        ++num_tries_after_min;
      }
    }
  }
}

static VP8LMultipliers GetBestColorTransformForTile(
    int tile_x, int tile_y, int bits,
    VP8LMultipliers prev_x,
    VP8LMultipliers prev_y,
    int quality, int xsize, int ysize,
    const int accumulated_red_histo[256],
    const int accumulated_blue_histo[256],
    const uint32_t* const argb) {
  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;
  const int all_x_max = GetMin(tile_x_offset + max_tile_size, xsize);
  const int all_y_max = GetMin(tile_y_offset + max_tile_size, ysize);
  VP8LMultipliers best_tx;
  MultipliersClear(&best_tx);

  GetBestGreenToRed(tile_x_offset, tile_y_offset, all_x_max, all_y_max, xsize,
                    prev_x, prev_y, accumulated_red_histo, argb, &best_tx);
  GetBestGreenRedToBlue(tile_x_offset, tile_y_offset, all_x_max, all_y_max,
                        xsize, prev_x, prev_y, quality, accumulated_blue_histo,
                        argb, &best_tx);
  return best_tx;
}

static void CopyTileWithColorTransform(int xsize, int ysize,
                                       int tile_x, int tile_y,
                                       int max_tile_size,
                                       VP8LMultipliers color_transform,
                                       uint32_t* argb) {
  const int xscan = GetMin(max_tile_size, xsize - tile_x);
  int yscan = GetMin(max_tile_size, ysize - tile_y);
  argb += tile_y * xsize + tile_x;
  while (yscan-- > 0) {
    VP8LTransformColor(&color_transform, argb, xscan);
    argb += xsize;
  }
}

void VP8LColorSpaceTransform(int width, int height, int bits, int quality,
                             uint32_t* const argb, uint32_t* image) {
  const int max_tile_size = 1 << bits;
  const int tile_xsize = VP8LSubSampleSize(width, bits);
  const int tile_ysize = VP8LSubSampleSize(height, bits);
  int accumulated_red_histo[256] = { 0 };
  int accumulated_blue_histo[256] = { 0 };
  int tile_x, tile_y;
  VP8LMultipliers prev_x, prev_y;
  MultipliersClear(&prev_y);
  MultipliersClear(&prev_x);
  for (tile_y = 0; tile_y < tile_ysize; ++tile_y) {
    for (tile_x = 0; tile_x < tile_xsize; ++tile_x) {
      int y;
      const int tile_x_offset = tile_x * max_tile_size;
      const int tile_y_offset = tile_y * max_tile_size;
      const int all_x_max = GetMin(tile_x_offset + max_tile_size, width);
      const int all_y_max = GetMin(tile_y_offset + max_tile_size, height);
      const int offset = tile_y * tile_xsize + tile_x;
      if (tile_y != 0) {
        ColorCodeToMultipliers(image[offset - tile_xsize], &prev_y);
      }
      prev_x = GetBestColorTransformForTile(tile_x, tile_y, bits,
                                            prev_x, prev_y,
                                            quality, width, height,
                                            accumulated_red_histo,
                                            accumulated_blue_histo,
                                            argb);
      image[offset] = MultipliersToColorCode(&prev_x);
      CopyTileWithColorTransform(width, height, tile_x_offset, tile_y_offset,
                                 max_tile_size, prev_x, argb);

      // Gather accumulated histogram data.
      for (y = tile_y_offset; y < all_y_max; ++y) {
        int ix = y * width + tile_x_offset;
        const int ix_end = ix + all_x_max - tile_x_offset;
        for (; ix < ix_end; ++ix) {
          const uint32_t pix = argb[ix];
          if (ix >= 2 &&
              pix == argb[ix - 2] &&
              pix == 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] &&
              pix == argb[ix - width]) {
            continue;  // repeated pixels are handled by backward references
          }
          ++accumulated_red_histo[(pix >> 16) & 0xff];
          ++accumulated_blue_histo[(pix >> 0) & 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 tile_width = 1 << transform->bits_;
  const int mask = tile_width - 1;
  const int safe_width = width & ~mask;
  const int remaining_width = width - safe_width;
  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;
    VP8LMultipliers m = { 0, 0, 0 };
    const uint32_t* const data_safe_end = data + safe_width;
    const uint32_t* const data_end = data + width;
    while (data < data_safe_end) {
      ColorCodeToMultipliers(*pred++, &m);
      VP8LTransformColorInverse(&m, data, tile_width);
      data += tile_width;
    }
    if (data < data_end) {  // Left-overs using C-version.
      ColorCodeToMultipliers(*pred++, &m);
      VP8LTransformColorInverse(&m, data, remaining_width);
      data += remaining_width;
    }
    ++y;
    if ((y & mask) == 0) pred_row += tiles_per_row;;
  }
}

// Separate out pixels packed together using pixel-bundling.
// We define two methods for ARGB data (uint32_t) and alpha-only data (uint8_t).
#define COLOR_INDEX_INVERSE(FUNC_NAME, TYPE, GET_INDEX, GET_VALUE)             \
void FUNC_NAME(const VP8LTransform* const transform,                           \
               int y_start, int y_end, const TYPE* src, TYPE* 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                */  \
        /* 'pixels_per_byte' 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 = GET_INDEX(*src++);          \
        *dst++ = GET_VALUE(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++ = GET_VALUE(color_map[GET_INDEX(*src++)]);                      \
      }                                                                        \
    }                                                                          \
  }                                                                            \
}

static WEBP_INLINE uint32_t GetARGBIndex(uint32_t idx) {
  return (idx >> 8) & 0xff;
}

static WEBP_INLINE uint8_t GetAlphaIndex(uint8_t idx) {
  return idx;
}

static WEBP_INLINE uint32_t GetARGBValue(uint32_t val) {
  return val;
}

static WEBP_INLINE uint8_t GetAlphaValue(uint32_t val) {
  return (val >> 8) & 0xff;
}

static COLOR_INDEX_INVERSE(ColorIndexInverseTransform, uint32_t, GetARGBIndex,
                           GetARGBValue)
COLOR_INDEX_INVERSE(VP8LColorIndexInverseTransformAlpha, uint8_t, GetAlphaIndex,
                    GetAlphaValue)

#undef COLOR_INDEX_INVERSE

void VP8LInverseTransform(const VP8LTransform* const transform,
                          int row_start, int row_end,
                          const uint32_t* const in, uint32_t* const out) {
  const int width = transform->xsize_;
  assert(row_start < row_end);
  assert(row_end <= transform->ysize_);
  switch (transform->type_) {
    case SUBTRACT_GREEN:
      VP8LAddGreenToBlueAndRed(out, (row_end - row_start) * width);
      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.
        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:
      if (in == out && transform->bits_ > 0) {
        // Move packed pixels to the end of unpacked region, so that unpacking
        // can occur seamlessly.
        // Also, note that this is the only transform that applies on
        // the effective width of VP8LSubSampleSize(xsize_, bits_). All other
        // transforms work on effective width of xsize_.
        const int out_stride = (row_end - row_start) * width;
        const int in_stride = (row_end - row_start) *
            VP8LSubSampleSize(transform->xsize_, transform->bits_);
        uint32_t* const src = out + out_stride - in_stride;
        memmove(src, out, in_stride * sizeof(*src));
        ColorIndexInverseTransform(transform, row_start, row_end, src, out);
      } else {
        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);
}

void VP8LConvertBGRAToRGB_C(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;
  }
}

void VP8LConvertBGRAToRGBA_C(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;
  }
}

void VP8LConvertBGRAToRGBA4444_C(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++;
    const uint8_t rg = ((argb >> 16) & 0xf0) | ((argb >> 12) & 0xf);
    const uint8_t ba = ((argb >>  0) & 0xf0) | ((argb >> 28) & 0xf);
#ifdef WEBP_SWAP_16BIT_CSP
    *dst++ = ba;
    *dst++ = rg;
#else
    *dst++ = rg;
    *dst++ = ba;
#endif
  }
}

void VP8LConvertBGRAToRGB565_C(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++;
    const uint8_t rg = ((argb >> 16) & 0xf8) | ((argb >> 13) & 0x7);
    const uint8_t gb = ((argb >>  5) & 0xe0) | ((argb >>  3) & 0x1f);
#ifdef WEBP_SWAP_16BIT_CSP
    *dst++ = gb;
    *dst++ = rg;
#else
    *dst++ = rg;
    *dst++ = gb;
#endif
  }
}

void VP8LConvertBGRAToBGR_C(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) {
      const uint32_t argb = *src++;

#if !defined(WORDS_BIGENDIAN)
#if !defined(WEBP_REFERENCE_IMPLEMENTATION)
      *(uint32_t*)dst = BSwap32(argb);
#else  // WEBP_REFERENCE_IMPLEMENTATION
      dst[0] = (argb >> 24) & 0xff;
      dst[1] = (argb >> 16) & 0xff;
      dst[2] = (argb >>  8) & 0xff;
      dst[3] = (argb >>  0) & 0xff;
#endif
#else  // WORDS_BIGENDIAN
      dst[0] = (argb >>  0) & 0xff;
      dst[1] = (argb >>  8) & 0xff;
      dst[2] = (argb >> 16) & 0xff;
      dst[3] = (argb >> 24) & 0xff;
#endif
      dst += sizeof(argb);
    }
  } 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:
      VP8LConvertBGRAToRGB(in_data, num_pixels, rgba);
      break;
    case MODE_RGBA:
      VP8LConvertBGRAToRGBA(in_data, num_pixels, rgba);
      break;
    case MODE_rgbA:
      VP8LConvertBGRAToRGBA(in_data, num_pixels, rgba);
      WebPApplyAlphaMultiply(rgba, 0, num_pixels, 1, 0);
      break;
    case MODE_BGR:
      VP8LConvertBGRAToBGR(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:
      VP8LConvertBGRAToRGBA4444(in_data, num_pixels, rgba);
      break;
    case MODE_rgbA_4444:
      VP8LConvertBGRAToRGBA4444(in_data, num_pixels, rgba);
      WebPApplyAlphaMultiply4444(rgba, num_pixels, 1, 0);
      break;
    case MODE_RGB_565:
      VP8LConvertBGRAToRGB565(in_data, num_pixels, rgba);
      break;
    default:
      assert(0);          // Code flow should not reach here.
  }
}

//------------------------------------------------------------------------------
// Bundles multiple (1, 2, 4 or 8) pixels into a single pixel.
void VP8LBundleColorMap(const uint8_t* const row, int width,
                        int xbits, uint32_t* const dst) {
  int x;
  if (xbits > 0) {
    const int bit_depth = 1 << (3 - xbits);
    const int mask = (1 << xbits) - 1;
    uint32_t code = 0xff000000;
    for (x = 0; x < width; ++x) {
      const int xsub = x & mask;
      if (xsub == 0) {
        code = 0xff000000;
      }
      code |= row[x] << (8 + bit_depth * xsub);
      dst[x >> xbits] = code;
    }
  } else {
    for (x = 0; x < width; ++x) dst[x] = 0xff000000 | (row[x] << 8);
  }
}

//------------------------------------------------------------------------------

static double ExtraCost(const uint32_t* population, int length) {
  int i;
  double cost = 0.;
  for (i = 2; i < length - 2; ++i) cost += (i >> 1) * population[i + 2];
  return cost;
}

static double ExtraCostCombined(const uint32_t* X, const uint32_t* Y,
                                int length) {
  int i;
  double cost = 0.;
  for (i = 2; i < length - 2; ++i) {
    const int xy = X[i + 2] + Y[i + 2];
    cost += (i >> 1) * xy;
  }
  return cost;
}

// Returns the various RLE counts
static VP8LStreaks HuffmanCostCount(const uint32_t* population, int length) {
  int i;
  int streak = 0;
  VP8LStreaks stats;
  memset(&stats, 0, sizeof(stats));
  for (i = 0; i < length - 1; ++i) {
    ++streak;
    if (population[i] == population[i + 1]) {
      continue;
    }
    stats.counts[population[i] != 0] += (streak > 3);
    stats.streaks[population[i] != 0][(streak > 3)] += streak;
    streak = 0;
  }
  ++streak;
  stats.counts[population[i] != 0] += (streak > 3);
  stats.streaks[population[i] != 0][(streak > 3)] += streak;
  return stats;
}

static VP8LStreaks HuffmanCostCombinedCount(const uint32_t* X,
                                            const uint32_t* Y, int length) {
  int i;
  int streak = 0;
  VP8LStreaks stats;
  memset(&stats, 0, sizeof(stats));
  for (i = 0; i < length - 1; ++i) {
    const int xy = X[i] + Y[i];
    const int xy_next = X[i + 1] + Y[i + 1];
    ++streak;
    if (xy == xy_next) {
      continue;
    }
    stats.counts[xy != 0] += (streak > 3);
    stats.streaks[xy != 0][(streak > 3)] += streak;
    streak = 0;
  }
  {
    const int xy = X[i] + Y[i];
    ++streak;
    stats.counts[xy != 0] += (streak > 3);
    stats.streaks[xy != 0][(streak > 3)] += streak;
  }
  return stats;
}

//------------------------------------------------------------------------------

static void HistogramAdd(const VP8LHistogram* const a,
                         const VP8LHistogram* const b,
                         VP8LHistogram* const out) {
  int i;
  const int literal_size = VP8LHistogramNumCodes(a->palette_code_bits_);
  assert(a->palette_code_bits_ == b->palette_code_bits_);
  if (b != out) {
    for (i = 0; i < literal_size; ++i) {
      out->literal_[i] = a->literal_[i] + b->literal_[i];
    }
    for (i = 0; i < NUM_DISTANCE_CODES; ++i) {
      out->distance_[i] = a->distance_[i] + b->distance_[i];
    }
    for (i = 0; i < NUM_LITERAL_CODES; ++i) {
      out->red_[i] = a->red_[i] + b->red_[i];
      out->blue_[i] = a->blue_[i] + b->blue_[i];
      out->alpha_[i] = a->alpha_[i] + b->alpha_[i];
    }
  } else {
    for (i = 0; i < literal_size; ++i) {
      out->literal_[i] += a->literal_[i];
    }
    for (i = 0; i < NUM_DISTANCE_CODES; ++i) {
      out->distance_[i] += a->distance_[i];
    }
    for (i = 0; i < NUM_LITERAL_CODES; ++i) {
      out->red_[i] += a->red_[i];
      out->blue_[i] += a->blue_[i];
      out->alpha_[i] += a->alpha_[i];
    }
  }
}

//------------------------------------------------------------------------------

VP8LProcessBlueAndRedFunc VP8LSubtractGreenFromBlueAndRed;
VP8LProcessBlueAndRedFunc VP8LAddGreenToBlueAndRed;
VP8LPredictorFunc VP8LPredictors[16];

VP8LTransformColorFunc VP8LTransformColor;
VP8LTransformColorFunc VP8LTransformColorInverse;

VP8LConvertFunc VP8LConvertBGRAToRGB;
VP8LConvertFunc VP8LConvertBGRAToRGBA;
VP8LConvertFunc VP8LConvertBGRAToRGBA4444;
VP8LConvertFunc VP8LConvertBGRAToRGB565;
VP8LConvertFunc VP8LConvertBGRAToBGR;

VP8LFastLog2SlowFunc VP8LFastLog2Slow;
VP8LFastLog2SlowFunc VP8LFastSLog2Slow;

VP8LCostFunc VP8LExtraCost;
VP8LCostCombinedFunc VP8LExtraCostCombined;

VP8LCostCountFunc VP8LHuffmanCostCount;
VP8LCostCombinedCountFunc VP8LHuffmanCostCombinedCount;

VP8LHistogramAddFunc VP8LHistogramAdd;

extern void VP8LDspInitSSE2(void);
extern void VP8LDspInitNEON(void);
extern void VP8LDspInitMIPS32(void);

void VP8LDspInit(void) {
  memcpy(VP8LPredictors, kPredictorsC, sizeof(VP8LPredictors));

  VP8LSubtractGreenFromBlueAndRed = VP8LSubtractGreenFromBlueAndRed_C;
  VP8LAddGreenToBlueAndRed = VP8LAddGreenToBlueAndRed_C;

  VP8LTransformColor = VP8LTransformColor_C;
  VP8LTransformColorInverse = VP8LTransformColorInverse_C;

  VP8LConvertBGRAToRGB = VP8LConvertBGRAToRGB_C;
  VP8LConvertBGRAToRGBA = VP8LConvertBGRAToRGBA_C;
  VP8LConvertBGRAToRGBA4444 = VP8LConvertBGRAToRGBA4444_C;
  VP8LConvertBGRAToRGB565 = VP8LConvertBGRAToRGB565_C;
  VP8LConvertBGRAToBGR = VP8LConvertBGRAToBGR_C;

  VP8LFastLog2Slow = FastLog2Slow;
  VP8LFastSLog2Slow = FastSLog2Slow;

  VP8LExtraCost = ExtraCost;
  VP8LExtraCostCombined = ExtraCostCombined;

  VP8LHuffmanCostCount = HuffmanCostCount;
  VP8LHuffmanCostCombinedCount = HuffmanCostCombinedCount;

  VP8LHistogramAdd = HistogramAdd;

  // If defined, use CPUInfo() to overwrite some pointers with faster versions.
  if (VP8GetCPUInfo != NULL) {
#if defined(WEBP_USE_SSE2)
    if (VP8GetCPUInfo(kSSE2)) {
      VP8LDspInitSSE2();
    }
#endif
#if defined(WEBP_USE_NEON)
    if (VP8GetCPUInfo(kNEON)) {
      VP8LDspInitNEON();
    }
#endif
#if defined(WEBP_USE_MIPS32)
    if (VP8GetCPUInfo(kMIPS32)) {
      VP8LDspInitMIPS32();
    }
#endif
  }
}

//------------------------------------------------------------------------------