mirror of
https://github.com/aicodix/code.git
synced 2026-04-27 14:30:36 +00:00
56 lines
1.2 KiB
C++
56 lines
1.2 KiB
C++
/*
|
|
Decoder for short BCH codes
|
|
|
|
Copyright 2020 Ahmet Inan <inan@aicodix.de>
|
|
*/
|
|
|
|
#pragma once
|
|
|
|
namespace CODE {
|
|
|
|
template <int N, int K>
|
|
class ShortBCHCodeDecoder
|
|
{
|
|
static const int P = N - K;
|
|
static const int W = 1 << K;
|
|
static const int R = 1 << P;
|
|
int err[R];
|
|
short par[W];
|
|
static_assert(N < 8 * sizeof(err[0]), "codeword type not wide enough");
|
|
static_assert(P < 8 * sizeof(par[0]), "parity type not wide enough");
|
|
static int modgen(int inp, int gen)
|
|
{
|
|
for (int i = K-1; i >= 0; --i) {
|
|
int tmp = inp >> (i+P);
|
|
inp ^= (tmp & 1) * (gen << i);
|
|
}
|
|
return inp;
|
|
}
|
|
public:
|
|
ShortBCHCodeDecoder(int generator, int T)
|
|
{
|
|
for (int i = 0; i < W; ++i)
|
|
par[i] = modgen(i << P, generator);
|
|
err[0] = 0;
|
|
assert(T > 0 && T <= 4);
|
|
for (int a = 1<<(N-1); T >= 1 && a; a >>= 1) {
|
|
err[modgen(a, generator)] = a;
|
|
for (int b = a >> 1; T >= 2 && b; b >>= 1) {
|
|
err[modgen(a|b, generator)] = a|b;
|
|
for (int c = b >> 1; T >= 3 && c; c >>= 1) {
|
|
err[modgen(a|b|c, generator)] = a|b|c;
|
|
for (int d = c >> 1; T >= 4 && d; d >>= 1) {
|
|
err[modgen(a|b|c|d, generator)] = a|b|c|d;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
int operator()(int inp)
|
|
{
|
|
return inp ^ err[(par[inp>>P] ^ inp) & (R-1)];
|
|
}
|
|
};
|
|
|
|
}
|
|
|