BaseTools/Source/C/BrotliCompress/enc/bit_cost_inc.h

   1 /* NOLINT(build/header_guard) */
   2 /* Copyright 2013 Google Inc. All Rights Reserved.
   3
   4    Distributed under MIT license.
   5    See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
   6 */
   7
   8 /* template parameters: FN */
   9
  10 #define HistogramType FN(Histogram)
  11
  12 double FN(BrotliPopulationCost)(const HistogramType* histogram) {
  13   static const double kOneSymbolHistogramCost = 12;
  14   static const double kTwoSymbolHistogramCost = 20;
  15   static const double kThreeSymbolHistogramCost = 28;
  16   static const double kFourSymbolHistogramCost = 37;
  17   const size_t data_size = FN(HistogramDataSize)();
  18   int count = 0;
  19   size_t s[5];
  20   double bits = 0.0;
  21   size_t i;
  22   if (histogram->total_count_ == 0) {
  23     return kOneSymbolHistogramCost;
  24   }
  25   for (i = 0; i < data_size; ++i) {
  26     if (histogram->data_[i] > 0) {
  27       s[count] = i;
  28       ++count;
  29       if (count > 4) break;
  30     }
  31   }
  32   if (count == 1) {
  33     return kOneSymbolHistogramCost;
  34   }
  35   if (count == 2) {
  36     return (kTwoSymbolHistogramCost + (double)histogram->total_count_);
  37   }
  38   if (count == 3) {
  39     const uint32_t histo0 = histogram->data_[s[0]];
  40     const uint32_t histo1 = histogram->data_[s[1]];
  41     const uint32_t histo2 = histogram->data_[s[2]];
  42     const uint32_t histomax =
  43         BROTLI_MAX(uint32_t, histo0, BROTLI_MAX(uint32_t, histo1, histo2));
  44     return (kThreeSymbolHistogramCost +
  45             2 * (histo0 + histo1 + histo2) - histomax);
  46   }
  47   if (count == 4) {
  48     uint32_t histo[4];
  49     uint32_t h23;
  50     uint32_t histomax;
  51     for (i = 0; i < 4; ++i) {
  52       histo[i] = histogram->data_[s[i]];
  53     }
  54     /* Sort */
  55     for (i = 0; i < 4; ++i) {
  56       size_t j;
  57       for (j = i + 1; j < 4; ++j) {
  58         if (histo[j] > histo[i]) {
  59           BROTLI_SWAP(uint32_t, histo, j, i);
  60         }
  61       }
  62     }
  63     h23 = histo[2] + histo[3];
  64     histomax = BROTLI_MAX(uint32_t, h23, histo[0]);
  65     return (kFourSymbolHistogramCost +
  66             3 * h23 + 2 * (histo[0] + histo[1]) - histomax);
  67   }
  68
  69   {
  70     /* In this loop we compute the entropy of the histogram and simultaneously
  71        build a simplified histogram of the code length codes where we use the
  72        zero repeat code 17, but we don't use the non-zero repeat code 16. */
  73     size_t max_depth = 1;
  74     uint32_t depth_histo[BROTLI_CODE_LENGTH_CODES] = { 0 };
  75     const double log2total = FastLog2(histogram->total_count_);
  76     for (i = 0; i < data_size;) {
  77       if (histogram->data_[i] > 0) {
  78         /* Compute -log2(P(symbol)) = -log2(count(symbol)/total_count) =
  79                                     = log2(total_count) - log2(count(symbol)) */
  80         double log2p = log2total - FastLog2(histogram->data_[i]);
  81         /* Approximate the bit depth by round(-log2(P(symbol))) */
  82         size_t depth = (size_t)(log2p + 0.5);
  83         bits += histogram->data_[i] * log2p;
  84         if (depth > 15) {
  85           depth = 15;
  86         }
  87         if (depth > max_depth) {
  88           max_depth = depth;
  89         }
  90         ++depth_histo[depth];
  91         ++i;
  92       } else {
  93         /* Compute the run length of zeros and add the appropriate number of 0
  94            and 17 code length codes to the code length code histogram. */
  95         uint32_t reps = 1;
  96         size_t k;
  97         for (k = i + 1; k < data_size && histogram->data_[k] == 0; ++k) {
  98           ++reps;
  99         }
 100         i += reps;
 101         if (i == data_size) {
 102           /* Don't add any cost for the last zero run, since these are encoded
 103              only implicitly. */
 104           break;
 105         }
 106         if (reps < 3) {
 107           depth_histo[0] += reps;
 108         } else {
 109           reps -= 2;
 110           while (reps > 0) {
 111             ++depth_histo[BROTLI_REPEAT_ZERO_CODE_LENGTH];
 112             /* Add the 3 extra bits for the 17 code length code. */
 113             bits += 3;
 114             reps >>= 3;
 115           }
 116         }
 117       }
 118     }
 119     /* Add the estimated encoding cost of the code length code histogram. */
 120     bits += (double)(18 + 2 * max_depth);
 121     /* Add the entropy of the code length code histogram. */
 122     bits += BitsEntropy(depth_histo, BROTLI_CODE_LENGTH_CODES);
 123   }
 124   return bits;
 125 }
 126
 127 #undef HistogramType