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added encoder and soft decoder for simplex codes

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Ahmet Inan 2020-05-31 17:43:29 +02:00
commit 620466021b
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simplex_decoder.hh Normal file
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/*
Soft decoder for Simplex codes
Copyright 2020 Ahmet Inan <inan@aicodix.de>
*/
#pragma once
namespace CODE {
template <int K>
class SimplexDecoder
{
static const int W = 1 << K;
static const int N = (1 << K) - 1;
int8_t mod[W*N];
static bool parity(unsigned x)
{
x ^= x >> 16;
x ^= x >> 8;
x ^= x >> 4;
x ^= x >> 2;
x ^= x >> 1;
return x & 1;
}
public:
SimplexDecoder()
{
for (int msg = 0; msg < W; ++msg)
for (int i = 0; i < N; ++i)
mod[msg*N+i] = 1 - 2 * parity(msg&(i+1));
}
int operator()(const int8_t *code)
{
int word = 0, best = 0, next = 0;
for (int msg = 0; msg < W; ++msg) {
int sum = 0;
for (int i = 0; i < N; ++i)
sum += mod[msg*N+i] * code[i];
if (sum > best) {
next = best;
best = sum;
word = msg;
} else if (sum > next) {
next = sum;
}
}
if (best == next)
return -1;
return word;
}
};
}