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