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remove use of log2(). Use VP8LFastLog2() instead.

Browse Source 
Order-by-cost mostly unchanged (up to a scaling constant 1/log(2))
(except for few minor diff in < 2% of cases)

+ remove unused field cost_mode->cache_bits_

Change-Id: I714f8ab12f49a23f5d499a64c741382c9b489a3e
This commit is contained in:
Pascal Massimino
2012-08-01 18:22:06 -07:00
parent 8c515d54ea
commit 323dc4d9b9
5 changed files with 214 additions and 192 deletions
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55
src/enc/histogram.c
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@ -19,17 +19,6 @@
#include "../dsp/lossless.h"
#include "../utils/utils.h"
#if defined(_MSC_VER) && !defined(NOT_HAVE_LOG2)
# define NOT_HAVE_LOG2 1
#endif
#ifdef NOT_HAVE_LOG2
static WEBP_INLINE double log2(double d) {
const double kLog2Reciprocal = 1.442695040888963;
return log(d) * kLog2Reciprocal;
}
#endif
static void HistogramClear(VP8LHistogram* const p) {
memset(p->literal_, 0, sizeof(p->literal_));
memset(p->red_, 0, sizeof(p->red_));
@ -88,33 +77,6 @@ VP8LHistogramSet* VP8LAllocateHistogramSet(int size, int cache_bits) {
// -----------------------------------------------------------------------------
void VP8LConvertPopulationCountTableToBitEstimates(
int num_symbols, const int population_counts[], double output[]) {
int sum = 0;
int nonzeros = 0;
int i;
for (i = 0; i < num_symbols; ++i) {
sum += population_counts[i];
if (population_counts[i] > 0) {
++nonzeros;
}
}
if (nonzeros <= 1) {
memset(output, 0, num_symbols * sizeof(*output));
return;
}
{
const double log2sum = log2(sum);
for (i = 0; i < num_symbols; ++i) {
if (population_counts[i] == 0) {
output[i] = log2sum;
} else {
output[i] = log2sum - log2(population_counts[i]);
}
}
}
}
void VP8LHistogramAddSinglePixOrCopy(VP8LHistogram* const histo,
const PixOrCopy* const v) {
if (PixOrCopyIsLiteral(v)) {
@ -139,7 +101,7 @@ void VP8LHistogramAddSinglePixOrCopy(VP8LHistogram* const histo,
static double BitsEntropy(const int* const array, int n) {
double retval = 0;
double retval = 0.;
int sum = 0;
int nonzeros = 0;
int max_val = 0;
@ -149,15 +111,14 @@ static double BitsEntropy(const int* const array, int n) {
if (array[i] != 0) {
sum += array[i];
++nonzeros;
retval += array[i] * VP8LFastLog(array[i]);
retval -= VP8LFastSLog2(array[i]);
if (max_val < array[i]) {
max_val = array[i];
}
}
}
retval -= sum * VP8LFastLog(sum);
retval *= -1.4426950408889634; // 1.0 / -Log(2);
mix = 0.627;
retval += VP8LFastSLog2(sum);
if (nonzeros < 5) {
if (nonzeros <= 1) {
return 0;
@ -177,15 +138,15 @@ static double BitsEntropy(const int* const array, int n) {
} else {
mix = 0.7; // nonzeros == 4.
}
} else {
mix = 0.627;
}
{
double min_limit = 2 * sum - max_val;
min_limit = mix * min_limit + (1.0 - mix) * retval;
if (retval < min_limit) {
return min_limit;
}
return (retval < min_limit) ? min_limit : retval;
}
return retval;
}
double VP8LHistogramEstimateBitsBulk(const VP8LHistogram* const p) {