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includes/std: Optimize std::bit::popcount

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WerWolv
2024-07-04 17:58:12 +02:00
parent 5380877da4
commit f797c711ca
1 changed files with 7 additions and 3 deletions
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10
includes/std/bit.pat
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@@ -14,9 +14,13 @@ namespace auto std::bit {
@return The number of bits set to 1 in `x` @return The number of bits set to 1 in `x`
*/ */
fn popcount(u128 x) { fn popcount(u128 x) {
x = (x & (std::limits::u128_max() / 3)) + ((x >> 1) & (std::limits::u128_max() / 3)); const u128 a = 0x55555555555555555555555555555555;
x = (x & (std::limits::u128_max() / 5)) + ((x >> 2) & (std::limits::u128_max() / 5)); const u128 b = 0x33333333333333333333333333333333;
x = (x & (std::limits::u128_max() / 17)) + ((x >> 4) & (std::limits::u128_max() / 17)); const u128 c = 0x0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F;
x = (x & a) + ((x >> 1) & a);
x = (x & b) + ((x >> 2) & b);
x = (x & c) + ((x >> 4) & c);
return x % 0xFF; return x % 0xFF;
}; };