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/* Copyright 2013 Google Inc. All Rights Reserved.
Distributed under MIT license.
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/
/* Functions to estimate the bit cost of Huffman trees. */
#ifndef BROTLI_ENC_BIT_COST_H_
#define BROTLI_ENC_BIT_COST_H_
#include "../common/platform.h"
#include <brotli/types.h>
#include "./fast_log.h"
#include "./histogram.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
static BROTLI_INLINE double ShannonEntropy(
const uint32_t* population, size_t size, size_t* total) {
size_t sum = 0;
double retval = 0;
const uint32_t* population_end = population + size;
size_t p;
if (size & 1) {
goto odd_number_of_elements_left;
}
while (population < population_end) {
p = *population++;
sum += p;
retval -= (double)p * FastLog2(p);
odd_number_of_elements_left:
p = *population++;
sum += p;
retval -= (double)p * FastLog2(p);
}
if (sum) retval += (double)sum * FastLog2(sum);
*total = sum;
return retval;
}
static BROTLI_INLINE double BitsEntropy(
const uint32_t* population, size_t size) {
size_t sum;
double retval = ShannonEntropy(population, size, &sum);
if (retval < sum) {
/* At least one bit per literal is needed. */
retval = (double)sum;
}
return retval;
}
BROTLI_INTERNAL double BrotliPopulationCostLiteral(const HistogramLiteral*);
BROTLI_INTERNAL double BrotliPopulationCostCommand(const HistogramCommand*);
BROTLI_INTERNAL double BrotliPopulationCostDistance(const HistogramDistance*);
#if defined(__cplusplus) || defined(c_plusplus)
} /* extern "C" */
#endif
#endif /* BROTLI_ENC_BIT_COST_H_ */
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