180a181,213
> /**
> * Checks if a number is a power of two, or zero.
> */
> template <class T>
> inline bool
> isPow2(T v) {
> return (v & (v - 1)) == (T)0;
> }
>
> /**
> * Returns the number of set ones in the provided value.
> * PD algorithm from
> * http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
> */
> inline int
> popCount(uint64_t val) {
> #ifndef __has_builtin
> #define __has_builtin(foo) 0
> #endif
> #if defined(__GNUC__) || (defined(__clang__) && __has_builtin(__builtin_popcountl))
> return __builtin_popcountl(val);
> #else
> const uint64_t m1 = 0x5555555555555555; // ..010101b
> const uint64_t m2 = 0x3333333333333333; // ..110011b
> const uint64_t m4 = 0x0f0f0f0f0f0f0f0f; // ..001111b
> const uint64_t sum = 0x0101010101010101;
>
> val -= (val >> 1) & m1; // 2 bits count -> 2 bits
> val = (val & m2) + ((val >> 2) & m2); // 4 bits count -> 4 bits
> val = (val + (val >> 4)) & m4; // 8 bits count -> 8 bits
> return (val * sum) >> 56; // horizontal sum
> #endif // defined(__GNUC__) || (defined(__clang__) && __has_builtin(__builtin_popcountl))
> }