github.com/cockroachdb/cockroach@v20.2.0-alpha.1+incompatible/pkg/util/encoding/complement_fast.go (about)

     1  // Copyright 2015 The Cockroach Authors.
     2  //
     3  // Use of this software is governed by the Business Source License
     4  // included in the file licenses/BSL.txt.
     5  //
     6  // As of the Change Date specified in that file, in accordance with
     7  // the Business Source License, use of this software will be governed
     8  // by the Apache License, Version 2.0, included in the file
     9  // licenses/APL.txt.
    10  
    11  // +build 386 amd64
    12  
    13  package encoding
    14  
    15  import "unsafe"
    16  
    17  // The idea for the fast ones complement is borrowed from fastXORBytes
    18  // in the crypto standard library.
    19  const wordSize = int(unsafe.Sizeof(uintptr(0)))
    20  
    21  func onesComplement(b []byte) {
    22  	n := len(b)
    23  	w := n / wordSize
    24  	if w > 0 {
    25  		bw := *(*[]uintptr)(unsafe.Pointer(&b))
    26  		for i := 0; i < w; i++ {
    27  			bw[i] = ^bw[i]
    28  		}
    29  	}
    30  
    31  	for i := w * wordSize; i < n; i++ {
    32  		b[i] = ^b[i]
    33  	}
    34  }