1 // Copyright 2018 The gVisor Authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 15 //go:build !amd64 && !arm64
16 // +build !amd64,!arm64
17 18 package bits
19 20 // TrailingZeros64 returns the number of bits before the least significant 1
21 // bit in x; in other words, it returns the index of the least significant 1
22 // bit in x. If x is 0, TrailingZeros64 returns 64.
23 func TrailingZeros64(x uint64) int {
24 if x == 0 {
25 return 64
26 }
27 i := 0
28 for ; x&1 == 0; i++ {
29 x >>= 1
30 }
31 return i
32 }
33 34 // MostSignificantOne64 returns the index of the most significant 1 bit in
35 // x. If x is 0, MostSignificantOne64 returns 64.
36 func MostSignificantOne64(x uint64) int {
37 if x == 0 {
38 return 64
39 }
40 i := 63
41 for ; x&(1<<63) == 0; i-- {
42 x <<= 1
43 }
44 return i
45 }
46 47 // ForEachSetBit64 calls f once for each set bit in x, with argument i equal to
48 // the set bit's index.
49 func ForEachSetBit64(x uint64, f func(i int)) {
50 for i := 0; x != 0; i++ {
51 if x&1 != 0 {
52 f(i)
53 }
54 x >>= 1
55 }
56 }
57