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73bb3c8530
- Improved compression for triangular meshes (~10%) - Added WebAssembly decoder - Code cleanup + robustness fixes
34 lines
1003 B
C++
34 lines
1003 B
C++
#include "core/shannon_entropy.h"
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#include <cmath>
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#include <vector>
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namespace draco {
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int64_t ComputeShannonEntropy(const uint32_t *symbols, int num_symbols,
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int max_value, int *out_num_unique_symbols) {
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// First find frequency of all unique symbols in the input array.
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int num_unique_symbols = 0;
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std::vector<int> symbol_frequencies(max_value + 1, 0);
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for (int i = 0; i < num_symbols; ++i) {
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++symbol_frequencies[symbols[i]];
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}
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double total_bits = 0;
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double num_symbols_d = num_symbols;
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for (int i = 0; i < max_value + 1; ++i) {
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if (symbol_frequencies[i] > 0) {
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++num_unique_symbols;
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// Compute Shannon entropy for the symbol.
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total_bits +=
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symbol_frequencies[i] *
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std::log2(static_cast<double>(symbol_frequencies[i]) / num_symbols_d);
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}
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}
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if (out_num_unique_symbols)
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*out_num_unique_symbols = num_unique_symbols;
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// Entropy is always negative.
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return -total_bits;
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}
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} // namespace draco
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