1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
|
// +build !go1.9
package roaring
// bit population count, take from
// https://code.google.com/p/go/issues/detail?id=4988#c11
// credit: https://code.google.com/u/arnehormann/
// credit: https://play.golang.org/p/U7SogJ7psJ
// credit: http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
func popcount(x uint64) uint64 {
x -= (x >> 1) & 0x5555555555555555
x = (x>>2)&0x3333333333333333 + x&0x3333333333333333
x += x >> 4
x &= 0x0f0f0f0f0f0f0f0f
x *= 0x0101010101010101
return x >> 56
}
|
