prometheus/vendor/github.com/dgryski/go-bits/popcnt.go

16 lines
400 B
Go

// +build !amd64 appengine popcntgo
package bits
// Popcnt counts the number of bits set
func Popcnt(x uint64) uint64 {
// bit population count, see
// http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
x -= (x >> 1) & 0x5555555555555555
x = (x>>2)&0x3333333333333333 + x&0x3333333333333333
x += x >> 4
x &= 0x0f0f0f0f0f0f0f0f
x *= 0x0101010101010101
return x >> 56
}