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-rw-r--r--modules/brotli/enc/bit_cost_inc.h127
1 files changed, 127 insertions, 0 deletions
diff --git a/modules/brotli/enc/bit_cost_inc.h b/modules/brotli/enc/bit_cost_inc.h
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+++ b/modules/brotli/enc/bit_cost_inc.h
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+/* NOLINT(build/header_guard) */
+/* Copyright 2013 Google Inc. All Rights Reserved.
+
+ Distributed under MIT license.
+ See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+*/
+
+/* template parameters: FN */
+
+#define HistogramType FN(Histogram)
+
+double FN(BrotliPopulationCost)(const HistogramType* histogram) {
+ static const double kOneSymbolHistogramCost = 12;
+ static const double kTwoSymbolHistogramCost = 20;
+ static const double kThreeSymbolHistogramCost = 28;
+ static const double kFourSymbolHistogramCost = 37;
+ const size_t data_size = FN(HistogramDataSize)();
+ int count = 0;
+ size_t s[5];
+ double bits = 0.0;
+ size_t i;
+ if (histogram->total_count_ == 0) {
+ return kOneSymbolHistogramCost;
+ }
+ for (i = 0; i < data_size; ++i) {
+ if (histogram->data_[i] > 0) {
+ s[count] = i;
+ ++count;
+ if (count > 4) break;
+ }
+ }
+ if (count == 1) {
+ return kOneSymbolHistogramCost;
+ }
+ if (count == 2) {
+ return (kTwoSymbolHistogramCost + (double)histogram->total_count_);
+ }
+ if (count == 3) {
+ const uint32_t histo0 = histogram->data_[s[0]];
+ const uint32_t histo1 = histogram->data_[s[1]];
+ const uint32_t histo2 = histogram->data_[s[2]];
+ const uint32_t histomax =
+ BROTLI_MAX(uint32_t, histo0, BROTLI_MAX(uint32_t, histo1, histo2));
+ return (kThreeSymbolHistogramCost +
+ 2 * (histo0 + histo1 + histo2) - histomax);
+ }
+ if (count == 4) {
+ uint32_t histo[4];
+ uint32_t h23;
+ uint32_t histomax;
+ for (i = 0; i < 4; ++i) {
+ histo[i] = histogram->data_[s[i]];
+ }
+ /* Sort */
+ for (i = 0; i < 4; ++i) {
+ size_t j;
+ for (j = i + 1; j < 4; ++j) {
+ if (histo[j] > histo[i]) {
+ BROTLI_SWAP(uint32_t, histo, j, i);
+ }
+ }
+ }
+ h23 = histo[2] + histo[3];
+ histomax = BROTLI_MAX(uint32_t, h23, histo[0]);
+ return (kFourSymbolHistogramCost +
+ 3 * h23 + 2 * (histo[0] + histo[1]) - histomax);
+ }
+
+ {
+ /* In this loop we compute the entropy of the histogram and simultaneously
+ build a simplified histogram of the code length codes where we use the
+ zero repeat code 17, but we don't use the non-zero repeat code 16. */
+ size_t max_depth = 1;
+ uint32_t depth_histo[BROTLI_CODE_LENGTH_CODES] = { 0 };
+ const double log2total = FastLog2(histogram->total_count_);
+ for (i = 0; i < data_size;) {
+ if (histogram->data_[i] > 0) {
+ /* Compute -log2(P(symbol)) = -log2(count(symbol)/total_count) =
+ = log2(total_count) - log2(count(symbol)) */
+ double log2p = log2total - FastLog2(histogram->data_[i]);
+ /* Approximate the bit depth by round(-log2(P(symbol))) */
+ size_t depth = (size_t)(log2p + 0.5);
+ bits += histogram->data_[i] * log2p;
+ if (depth > 15) {
+ depth = 15;
+ }
+ if (depth > max_depth) {
+ max_depth = depth;
+ }
+ ++depth_histo[depth];
+ ++i;
+ } else {
+ /* Compute the run length of zeros and add the appropriate number of 0
+ and 17 code length codes to the code length code histogram. */
+ uint32_t reps = 1;
+ size_t k;
+ for (k = i + 1; k < data_size && histogram->data_[k] == 0; ++k) {
+ ++reps;
+ }
+ i += reps;
+ if (i == data_size) {
+ /* Don't add any cost for the last zero run, since these are encoded
+ only implicitly. */
+ break;
+ }
+ if (reps < 3) {
+ depth_histo[0] += reps;
+ } else {
+ reps -= 2;
+ while (reps > 0) {
+ ++depth_histo[BROTLI_REPEAT_ZERO_CODE_LENGTH];
+ /* Add the 3 extra bits for the 17 code length code. */
+ bits += 3;
+ reps >>= 3;
+ }
+ }
+ }
+ }
+ /* Add the estimated encoding cost of the code length code histogram. */
+ bits += (double)(18 + 2 * max_depth);
+ /* Add the entropy of the code length code histogram. */
+ bits += BitsEntropy(depth_histo, BROTLI_CODE_LENGTH_CODES);
+ }
+ return bits;
+}
+
+#undef HistogramType