mirror of https://github.com/AxioDL/zeus.git
Add Zeus::Math::PopCount
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@ -92,6 +92,22 @@ namespace Math
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float fastCosR(float val);
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float fastSinR(float val);
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int floorPowerOfTwo(int x);
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template <class T>
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inline int PopCount(T x)
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{
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using U = std::conditional_t<std::is_enum<T>::value, std::underlying_type_t<T>, T>;
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U cx = U(x);
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const U m1 = U(0x5555555555555555); //binary: 0101...
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const U m2 = U(0x3333333333333333); //binary: 00110011..
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const U m4 = U(0x0f0f0f0f0f0f0f0f); //binary: 4 zeros, 4 ones ...
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const U h01 = U(0x0101010101010101); //the sum of 256 to the power of 0,1,2,3...
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cx -= (cx >> 1) & m1; //put count of each 2 bits into those 2 bits
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cx = (cx & m2) + ((cx >> 2) & m2); //put count of each 4 bits into those 4 bits
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cx = (cx + (cx >> 4)) & m4; //put count of each 8 bits into those 8 bits
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return (cx * h01) >> ((sizeof(U)-1)*8); //returns left 8 bits of x + (x<<8) + (x<<16) + (x<<24) + ...
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}
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}
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}
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