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reordered forked metrics to benefit from a stable sort

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nth_element does not honor the established order, so previously good
candidates can still be thrown out when the scores are the same.
Using a stable_sort keeps the order but is more costly.
We don't have a stable_partial_sort unfortunately and the one
provided as example, implemented using partial_sort and two aditional
comparisions to make it stable, is slower than a stable_sort.
This commit is contained in:
Ahmet Inan 2024-03-02 12:00:43 +01:00
commit ed9521ba4b
2 changed files with 24 additions and 12 deletions
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18
polar_list_decoder.hh
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@ -55,24 +55,30 @@ struct PolarListNode<TYPE, 0>
TYPE sft = soft[1];
PATH fork[2*TYPE::SIZE];
for (int k = 0; k < TYPE::SIZE; ++k)
fork[k] = fork[k+TYPE::SIZE] = metric[k];
fork[2*k] = fork[2*k+1] = metric[k];
for (int k = 0; k < TYPE::SIZE; ++k)
if (sft.v[k] < 0)
fork[k] -= sft.v[k];
fork[2*k] -= sft.v[k];
else
fork[k+TYPE::SIZE] += sft.v[k];
fork[2*k+1] += sft.v[k];
int perm[2*TYPE::SIZE];
for (int k = 0; k < 2*TYPE::SIZE; ++k)
perm[k] = k;
std::nth_element(perm, perm+TYPE::SIZE, perm+2*TYPE::SIZE, [fork](int a, int b){ return fork[a] < fork[b]; });
#if 1
std::stable_sort(perm, perm+2*TYPE::SIZE, [fork](int a, int b){ return fork[a] < fork[b]; });
#else
std::partial_sort(perm, perm+TYPE::SIZE-1, perm+2*TYPE::SIZE, [fork](int a, int b){
return fork[a] < fork[b] ? true : fork[a] > fork[b] ? false : a < b;
});
#endif
for (int k = 0; k < TYPE::SIZE; ++k)
metric[k] = fork[perm[k]];
MAP map;
for (int k = 0; k < TYPE::SIZE; ++k)
map.v[k] = perm[k] % TYPE::SIZE;
map.v[k] = perm[k] >> 1;
TYPE hrd;
for (int k = 0; k < TYPE::SIZE; ++k)
hrd.v[k] = perm[k] < TYPE::SIZE ? 1 : -1;
hrd.v[k] = 1 - 2 * (perm[k] & 1);
message[*count] = hrd;
maps[*count] = map;
++*count;