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Use __builtin_popcountll for systems that support it

This commit is contained in:
Jack Andersen 2016-12-09 16:33:18 -10:00
parent 7185e13abe
commit a136d77458
1 changed files with 4 additions and 0 deletions
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4
include/zeus/Math.hpp
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@ -105,6 +105,9 @@ int ceilingPowerOfTwo(int x);
template <typename U>
typename std::enable_if<!std::is_enum<U>::value && std::is_integral<U>::value, int>::type PopCount(U x)
{
#if __GNUC__ >= 4
return __builtin_popcountll(x);
#else
const U m1 = U(0x5555555555555555); // binary: 0101...
const U m2 = U(0x3333333333333333); // binary: 00110011..
const U m4 = U(0x0f0f0f0f0f0f0f0f); // binary: 4 zeros, 4 ones ...
@ -114,6 +117,7 @@ typename std::enable_if<!std::is_enum<U>::value && std::is_integral<U>::value, i
x = (x & m2) + ((x >> 2) & m2); // put count of each 4 bits into those 4 bits
x = (x + (x >> 4)) & m4; // put count of each 8 bits into those 8 bits
return (x * h01) >> ((sizeof(U) - 1) * 8); // returns left 8 bits of x + (x<<8) + (x<<16) + (x<<24) + ...
#endif
}
template <typename E>