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61 lines
1.6 KiB
C++
61 lines
1.6 KiB
C++
// Copyright 1999-2015 Aske Simon Christensen. See LICENSE.txt for usage terms.
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/*
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A dummy entropy coder which estimates the size of coded symbols based on
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counts from a CountingCoder.
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*/
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#pragma once
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#include <vector>
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using std::vector;
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#include "CountingCoder.h"
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struct ContextSizes {
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unsigned short sizes[2];
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};
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class SizeMeasuringCoder : public Coder {
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static const int MIN_SIZE = 2;
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static const int MAX_SIZE = 12 << BIT_PRECISION;
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vector<ContextSizes> context_sizes;
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int sizeForCount(int count, int total) {
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int size = (int) floor(0.5 + log(total / (double) count) / log(2.0) * (1 << BIT_PRECISION));
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if (size < MIN_SIZE) size = MIN_SIZE;
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if (size > MAX_SIZE) size = MAX_SIZE;
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return size;
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}
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public:
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SizeMeasuringCoder(int n_contexts) {
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struct ContextSizes default_sizes = { { 1 << BIT_PRECISION, 1 << BIT_PRECISION } };
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context_sizes.resize(n_contexts, default_sizes);
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setCacheable(true);
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}
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SizeMeasuringCoder(CountingCoder *counting_coder) {
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context_sizes.resize(counting_coder->context_counts.size());
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for (int i = 0 ; i < counting_coder->context_counts.size() ; i++) {
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struct ContextSizes s;
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struct ContextCounts c = counting_coder->context_counts[i];
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int count0 = 1 + c.counts[0];
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int count1 = 1 + c.counts[1];
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int sum = count0 + count1;
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s.sizes[0] = sizeForCount(count0, sum);
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s.sizes[1] = sizeForCount(count1, sum);
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context_sizes[i] = s;
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}
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setCacheable(true);
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}
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virtual int code(int context_index, int bit) {
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return context_sizes[context_index].sizes[bit];
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}
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};
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