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complement_fast.go
38 lines (32 loc) · 1.01 KB
/
complement_fast.go
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// Copyright 2015 The Cockroach Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied. See the License for the specific language governing
// permissions and limitations under the License.
// +build 386 amd64
package encoding
import "unsafe"
// The idea for the fast ones complement is borrowed from fastXORBytes
// in the crypto standard library.
const wordSize = int(unsafe.Sizeof(uintptr(0)))
func onesComplement(b []byte) {
n := len(b)
w := n / wordSize
if w > 0 {
bw := *(*[]uintptr)(unsafe.Pointer(&b))
for i := 0; i < w; i++ {
bw[i] = ^bw[i]
}
}
for i := w * wordSize; i < n; i++ {
b[i] = ^b[i]
}
}