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forgejo/vendor/github.com/RoaringBitmap/roaring/clz_compat.go
2019-11-27 11:23:33 +02:00

36 lines
461 B
Go
Vendored

// +build !go1.9
package roaring
// LeadingZeroBits returns the number of consecutive most significant zero
// bits of x.
func countLeadingZeros(i uint64) int {
if i == 0 {
return 64
}
n := 1
x := uint32(i >> 32)
if x == 0 {
n += 32
x = uint32(i)
}
if (x >> 16) == 0 {
n += 16
x <<= 16
}
if (x >> 24) == 0 {
n += 8
x <<= 8
}
if x>>28 == 0 {
n += 4
x <<= 4
}
if x>>30 == 0 {
n += 2
x <<= 2
}
n -= int(x >> 31)
return n
}