github.com/cockroachdb/cockroachdb-parser@v0.23.3-0.20240213214944-911057d40c9a/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  //go:build 386 || amd64
    12  // +build 386 amd64
    13  
    14  package encoding
    15  
    16  import "unsafe"
    17  
    18  // The idea for the fast ones complement is borrowed from fastXORBytes
    19  // in the crypto standard library.
    20  const wordSize = int(unsafe.Sizeof(uintptr(0)))
    21  
    22  func onesComplement(b []byte) {
    23  	n := len(b)
    24  	w := n / wordSize
    25  	if w > 0 {
    26  		bw := *(*[]uintptr)(unsafe.Pointer(&b))
    27  		for i := 0; i < w; i++ {
    28  			bw[i] = ^bw[i]
    29  		}
    30  	}
    31  
    32  	for i := w * wordSize; i < n; i++ {
    33  		b[i] = ^b[i]
    34  	}
    35  }