mirror of https://github.com/go-gitea/gitea.git
46 lines
1.1 KiB
Go
46 lines
1.1 KiB
Go
// Copyright 2014-2019 Ulrich Kunitz. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
package lzma
|
|
|
|
/* Naming conventions follows the CodeReviewComments in the Go Wiki. */
|
|
|
|
// ntz32Const is used by the functions NTZ and NLZ.
|
|
const ntz32Const = 0x04d7651f
|
|
|
|
// ntz32Table is a helper table for de Bruijn algorithm by Danny Dubé.
|
|
// See Henry S. Warren, Jr. "Hacker's Delight" section 5-1 figure 5-26.
|
|
var ntz32Table = [32]int8{
|
|
0, 1, 2, 24, 3, 19, 6, 25,
|
|
22, 4, 20, 10, 16, 7, 12, 26,
|
|
31, 23, 18, 5, 21, 9, 15, 11,
|
|
30, 17, 8, 14, 29, 13, 28, 27,
|
|
}
|
|
|
|
// ntz32 computes the number of trailing zeros for an unsigned 32-bit integer.
|
|
func ntz32(x uint32) int {
|
|
if x == 0 {
|
|
return 32
|
|
}
|
|
x = (x & -x) * ntz32Const
|
|
return int(ntz32Table[x>>27])
|
|
}
|
|
|
|
// nlz32 computes the number of leading zeros for an unsigned 32-bit integer.
|
|
func nlz32(x uint32) int {
|
|
// Smear left most bit to the right
|
|
x |= x >> 1
|
|
x |= x >> 2
|
|
x |= x >> 4
|
|
x |= x >> 8
|
|
x |= x >> 16
|
|
// Use ntz mechanism to calculate nlz.
|
|
x++
|
|
if x == 0 {
|
|
return 0
|
|
}
|
|
x *= ntz32Const
|
|
return 32 - int(ntz32Table[x>>27])
|
|
}
|