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56 lines
892 B
C++
56 lines
892 B
C++
/*
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Soft decoder for Simplex codes
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Copyright 2020 Ahmet Inan <inan@aicodix.de>
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*/
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#pragma once
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namespace CODE {
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template <int K>
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class SimplexDecoder
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{
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static const int W = 1 << K;
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static const int N = (1 << K) - 1;
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int8_t mod[W*N];
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static bool parity(unsigned x)
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{
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x ^= x >> 16;
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x ^= x >> 8;
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x ^= x >> 4;
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x ^= x >> 2;
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x ^= x >> 1;
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return x & 1;
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}
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public:
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SimplexDecoder()
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{
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for (int msg = 0; msg < W; ++msg)
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for (int i = 0; i < N; ++i)
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mod[msg*N+i] = 1 - 2 * parity(msg&(i+1));
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}
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int operator()(const int8_t *code)
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{
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int word = 0, best = 0, next = 0;
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for (int msg = 0; msg < W; ++msg) {
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int sum = 0;
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for (int i = 0; i < N; ++i)
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sum += mod[msg*N+i] * code[i];
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if (sum > best) {
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next = best;
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best = sum;
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word = msg;
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} else if (sum > next) {
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next = sum;
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}
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}
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if (best == next)
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return -1;
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return word;
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}
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};
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}
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