64 lines
1.7 KiB
C
64 lines
1.7 KiB
C
/* 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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/* Functions to estimate the bit cost of Huffman trees. */
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#ifndef BROTLI_ENC_BIT_COST_H_
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#define BROTLI_ENC_BIT_COST_H_
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#include <brotli/types.h>
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#include "./fast_log.h"
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#include "./histogram.h"
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#include "./port.h"
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#if defined(__cplusplus) || defined(c_plusplus)
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extern "C" {
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#endif
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static BROTLI_INLINE double ShannonEntropy(const uint32_t *population,
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size_t size, size_t *total) {
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size_t sum = 0;
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double retval = 0;
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const uint32_t *population_end = population + size;
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size_t p;
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if (size & 1) {
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goto odd_number_of_elements_left;
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}
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while (population < population_end) {
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p = *population++;
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sum += p;
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retval -= (double)p * FastLog2(p);
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odd_number_of_elements_left:
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p = *population++;
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sum += p;
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retval -= (double)p * FastLog2(p);
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}
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if (sum) retval += (double)sum * FastLog2(sum);
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*total = sum;
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return retval;
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}
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static BROTLI_INLINE double BitsEntropy(
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const uint32_t *population, size_t size) {
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size_t sum;
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double retval = ShannonEntropy(population, size, &sum);
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if (retval < sum) {
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/* At least one bit per literal is needed. */
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retval = (double)sum;
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}
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return retval;
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}
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BROTLI_INTERNAL double BrotliPopulationCostLiteral(const HistogramLiteral*);
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BROTLI_INTERNAL double BrotliPopulationCostCommand(const HistogramCommand*);
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BROTLI_INTERNAL double BrotliPopulationCostDistance(const HistogramDistance*);
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#if defined(__cplusplus) || defined(c_plusplus)
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} /* extern "C" */
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#endif
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#endif /* BROTLI_ENC_BIT_COST_H_ */
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