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Proper SFINAE usage on PopCount

This commit is contained in:
Jack Andersen 2016-04-09 13:18:46 -10:00
parent eb2968304b
commit 286d098ecb
1 changed files with 15 additions and 8 deletions
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23
include/zeus/Math.hpp
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@ -94,21 +94,28 @@ float fastSinF(float val);
int floorPowerOfTwo(int x);
int ceilingPowerOfTwo(int x);
template <class T>
inline int PopCount(T x)
template <typename U>
typename std::enable_if<!std::is_enum<U>::value && std::is_integral<U>::value, int>::type
PopCount(U x)
{
using U = std::make_unsigned_t<std::conditional_t<std::is_enum<T>::value, std::underlying_type_t<T>, T>>;
U cx = U(x);
const U m1 = U(0x5555555555555555); //binary: 0101...
const U m2 = U(0x3333333333333333); //binary: 00110011..
const U m4 = U(0x0f0f0f0f0f0f0f0f); //binary: 4 zeros, 4 ones ...
const U h01 = U(0x0101010101010101); //the sum of 256 to the power of 0,1,2,3...
cx -= (cx >> 1) & m1; //put count of each 2 bits into those 2 bits
cx = (cx & m2) + ((cx >> 2) & m2); //put count of each 4 bits into those 4 bits
cx = (cx + (cx >> 4)) & m4; //put count of each 8 bits into those 8 bits
return (cx * h01) >> ((sizeof(U)-1)*8); //returns left 8 bits of x + (x<<8) + (x<<16) + (x<<24) + ...
x -= (x >> 1) & m1; //put count of each 2 bits into those 2 bits
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) + ...
}
template <typename E>
typename std::enable_if<std::is_enum<E>::value, int>::type
PopCount(E e)
{
return PopCount(static_cast<typename std::underlying_type<E>::type>(e));
}
}
#endif // MATH_HPP