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added support for packed bits in the BCH decoder

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This commit is contained in:
Ahmet Inan 2018-09-21 19:48:09 +02:00
commit de2ef34eb3
2 changed files with 73 additions and 19 deletions
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46
bose_chaudhuri_hocquenghem_decoder.hh
View file

@ -62,6 +62,52 @@ public:
corrections_count += !!magnitudes[i];
return corrections_count;
}
int compute_syndromes(uint8_t *code, ValueType *syndromes)
{
// $syndromes_i = code(pe^{FCR+i})$
for (int i = 0; i < NR; ++i)
syndromes[i] = ValueType((code[0] >> 7) & 1);
for (int j = 1; j < N; ++j) {
IndexType root(FCR), pe(1);
for (int i = 0; i < NR; ++i) {
syndromes[i] = fma(root, syndromes[i], ValueType((code[j / 8] >> (7 - j % 8)) & 1));
root *= pe;
}
}
int nonzero = 0;
for (int i = 0; i < NR; ++i)
nonzero += !!syndromes[i];
return nonzero;
}
int compute_syndromes(uint8_t *code, value_type *syndromes)
{
return compute_syndromes(code, reinterpret_cast<ValueType *>(syndromes));
}
int operator()(uint8_t *code, value_type *erasures = 0, int erasures_count = 0)
{
assert(0 <= erasures_count && erasures_count <= NR);
if (0) {
for (int i = 0; i < erasures_count; ++i)
code[erasures[i] / 8] &= ~(128 >> (erasures[i] % 8));
}
ValueType syndromes[NR];
if (!compute_syndromes(code, syndromes))
return 0;
IndexType locations[NR];
ValueType magnitudes[NR];
int count = algorithm(syndromes, locations, magnitudes, reinterpret_cast<IndexType *>(erasures), erasures_count);
if (count <= 0)
return count;
for (int i = 0; i < count; ++i)
if (1 < (int)magnitudes[i])
return -1;
for (int i = 0; i < count; ++i)
code[(int)locations[i] / 8] ^= (int)magnitudes[i] << (7 - (int)locations[i] % 8);
int corrections_count = 0;
for (int i = 0; i < count; ++i)
corrections_count += !!magnitudes[i];
return corrections_count;
}
};
}

46
tests/bch_decoder_test.cc
View file

@ -18,41 +18,49 @@ int main()
// NASA INTRO BCH(15, 5) T=3
typedef CODE::GaloisField<4, 0b10011, uint8_t> GF;
typedef CODE::BoseChaudhuriHocquenghemDecoder<6, 1, 5, GF> BCH;
const int L = (BCH::N + 7) / 8;
GF instance;
BCH decode;
uint8_t target[BCH::N] = { 1, 1, 0, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 1, 0 };
uint8_t code[BCH::N];
for (int i = 0; i < BCH::N; ++i)
uint8_t target[L] = { 0b11001000, 0b11110100 };
uint8_t code[L];
for (int i = 0; i < L; ++i)
code[i] = target[i];
std::uniform_int_distribution<uint8_t> distribution(0, BCH::N-1);
std::uniform_int_distribution<int> distribution(0, BCH::N-1);
auto noise = std::bind(distribution, generator);
for (int i = 0; i < 3; ++i)
code[noise()] ^= 1;
decode(reinterpret_cast<GF::ValueType *>(code));
for (int i = 0; i < BCH::N; ++i)
for (int i = 0; i < 3; ++i) {
int n = noise();
code[n / 8] ^= 128 >> (n % 8);
}
decode(code);
for (int i = 0; i < L; ++i)
assert(code[i] == target[i]);
}
if (1) {
// DVB-S2 FULL BCH(65535, 65343) T=12
typedef CODE::GaloisField<16, 0b10000000000101101, uint16_t> GF;
typedef CODE::BoseChaudhuriHocquenghemDecoder<24, 1, 65343, GF> BCH;
const int L = (BCH::N + 7) / 8;
GF *instance = new GF();
BCH *decode = new BCH();
uint16_t *target = new uint16_t[BCH::N];
uint8_t *target = new uint8_t[L];
for (int i = 0; i < L; ++i)
target[i] = 0;
for (int i = 0, s = 0; i < BCH::K; ++i, s=(s*(s*s*51767+71287)+35149)&0xffffff)
target[i] = (s^=s>>7)&1;
uint16_t parity[BCH::NP] = { 0, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 1, 1, 0, 1, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 0, 1, 0, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 0, 0 };
target[i/8] |= ((s^=s>>7)&1) << (7-i%8);
bool parity[BCH::NP] = { 0, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 1, 1, 0, 1, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 0, 1, 0, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 0, 0 };
for (int i = 0; i < BCH::NP; ++i)
target[BCH::K+i] = parity[i];
uint16_t *code = new uint16_t[BCH::N];
for (int i = 0; i < BCH::N; ++i)
target[(BCH::K+i)/8] |= parity[i] << (7-(BCH::K+i)%8);
uint8_t *code = new uint8_t[L];
for (int i = 0; i < L; ++i)
code[i] = target[i];
std::uniform_int_distribution<uint16_t> distribution(0, BCH::N-1);
std::uniform_int_distribution<int> distribution(0, BCH::N-1);
auto noise = std::bind(distribution, generator);
for (int i = 0; i < 12; ++i)
code[noise()] ^= 1;
(*decode)(reinterpret_cast<GF::ValueType *>(code));
for (int i = 0; i < BCH::N; ++i)
for (int i = 0; i < 12; ++i) {
int n = noise();
code[n / 8] ^= 128 >> (n % 8);
}
(*decode)(code);
for (int i = 0; i < L; ++i)
assert(code[i] == target[i]);
delete[] target;
delete[] code;