inet.af/netstack@v0.0.0-20220214151720-7585b01ddccf/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  //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  }