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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
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@ -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;
}
};
}