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optimized msb with http://graphics.stanford.edu/~seander/bithacks.html

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xtaci
2020-05-20 23:09:49 +08:00
parent 5052c856b8
commit 0276e0fe3b
1 changed files with 2 additions and 3 deletions
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alloc.go
+2 -3
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@@ -7,7 +7,7 @@ import (
var (
defaultAllocator *Allocator
debruijinPos = [...]byte{0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8, 31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9}
debruijinPos = [...]byte{0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31}
)
func init() {
@@ -68,6 +68,5 @@ func msb(size int) byte {
v |= v >> 4
v |= v >> 8
v |= v >> 16
v = (v >> 1) + 1
return debruijinPos[(v*0x077CB531)>>27]
return debruijinPos[(v*0x07C4ACDD)>>27]
}