github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/bits/uint64_arch_generic.go (about)

     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  // +build !amd64,!arm64
    16  
    17  package bits
    18  
    19  // TrailingZeros64 returns the number of bits before the least significant 1
    20  // bit in x; in other words, it returns the index of the least significant 1
    21  // bit in x. If x is 0, TrailingZeros64 returns 64.
    22  func TrailingZeros64(x uint64) int {
    23  	if x == 0 {
    24  		return 64
    25  	}
    26  	i := 0
    27  	for ; x&1 == 0; i++ {
    28  		x >>= 1
    29  	}
    30  	return i
    31  }
    32  
    33  // MostSignificantOne64 returns the index of the most significant 1 bit in
    34  // x. If x is 0, MostSignificantOne64 returns 64.
    35  func MostSignificantOne64(x uint64) int {
    36  	if x == 0 {
    37  		return 64
    38  	}
    39  	i := 63
    40  	for ; x&(1<<63) == 0; i-- {
    41  		x <<= 1
    42  	}
    43  	return i
    44  }
    45  
    46  // ForEachSetBit64 calls f once for each set bit in x, with argument i equal to
    47  // the set bit's index.
    48  func ForEachSetBit64(x uint64, f func(i int)) {
    49  	for i := 0; x != 0; i++ {
    50  		if x&1 != 0 {
    51  			f(i)
    52  		}
    53  		x >>= 1
    54  	}
    55  }