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pad horizontally to next size of machine word

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This commit is contained in:
Ahmet Inan 2020-08-06 20:00:56 +02:00
commit 304a7c8045
1 changed files with 24 additions and 20 deletions
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44
osd.hh
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@ -98,51 +98,53 @@ public:
template <int N, int K, int O>
class OrderedStatisticsDecoder
{
int8_t G[N*K];
int8_t codeword[N], candidate[N];
int8_t softperm[N];
int16_t perm[N];
static const int S = sizeof(size_t);
static const int W = (N+S-1) & ~(S-1);
int8_t G[W*K];
int8_t codeword[W], candidate[W];
int8_t softperm[W];
int16_t perm[W];
void row_echelon()
{
for (int k = 0; k < K; ++k) {
// find pivot in this column
for (int j = k; j < K; ++j) {
if (G[N*j+k]) {
if (G[W*j+k]) {
for (int i = k; j != k && i < N; ++i)
std::swap(G[N*j+i], G[N*k+i]);
std::swap(G[W*j+i], G[W*k+i]);
break;
}
}
// keep searching for suitable column for pivot
// beware: this will use columns >= K if necessary.
for (int j = k + 1; !G[N*k+k] && j < N; ++j) {
for (int j = k + 1; !G[W*k+k] && j < N; ++j) {
for (int h = k; h < K; ++h) {
if (G[N*h+j]) {
if (G[W*h+j]) {
// account column swap
std::swap(perm[k], perm[j]);
for (int i = 0; i < K; ++i)
std::swap(G[N*i+k], G[N*i+j]);
std::swap(G[W*i+k], G[W*i+j]);
for (int i = k; h != k && i < N; ++i)
std::swap(G[N*h+i], G[N*k+i]);
std::swap(G[W*h+i], G[W*k+i]);
break;
}
}
}
assert(G[N*k+k]);
assert(G[W*k+k]);
// zero out column entries below pivot
for (int j = k + 1; j < K; ++j)
if (G[N*j+k])
if (G[W*j+k])
for (int i = k; i < N; ++i)
G[N*j+i] ^= G[N*k+i];
G[W*j+i] ^= G[W*k+i];
}
}
void systematic()
{
for (int k = K-1; k; --k)
for (int j = 0; j < k; ++j)
if (G[N*j+k])
if (G[W*j+k])
for (int i = k; i < N; ++i)
G[N*j+i] ^= G[N*k+i];
G[W*j+i] ^= G[W*k+i];
}
void encode()
{
@ -150,18 +152,18 @@ class OrderedStatisticsDecoder
codeword[i] = codeword[0] & G[i];
for (int j = 1; j < K; ++j)
for (int i = K; i < N; ++i)
codeword[i] ^= codeword[j] & G[N*j+i];
codeword[i] ^= codeword[j] & G[W*j+i];
}
void flip(int j)
{
codeword[j] ^= 1;
for (int i = K; i < N; ++i)
codeword[i] ^= G[N*j+i];
for (int i = K; i < W; ++i)
codeword[i] ^= G[W*j+i];
}
static int metric(const int8_t *hard, const int8_t *soft)
{
int sum = 0;
for (int i = 0; i < N; ++i)
for (int i = 0; i < W; ++i)
sum += (1 - 2 * hard[i]) * soft[i];
return sum;
}
@ -173,11 +175,13 @@ public:
std::sort(perm, perm+N, [soft](int a, int b){ return std::abs(soft[a]) > std::abs(soft[b]); });
for (int j = 0; j < K; ++j)
for (int i = 0; i < N; ++i)
G[N*j+i] = genmat[N*j+perm[i]];
G[W*j+i] = genmat[N*j+perm[i]];
row_echelon();
systematic();
for (int i = 0; i < N; ++i)
softperm[i] = soft[perm[i]];
for (int i = N; i < W; ++i)
softperm[i] = 0;
for (int i = 0; i < K; ++i)
codeword[i] = softperm[i] < 0;
encode();