1// Copyright 2018 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// Package alias implements memory aliasing tests.
6// This code also exists as golang.org/x/crypto/internal/alias.
7package alias
8
9import "unsafe"
10
11// AnyOverlap reports whether x and y share memory at any (not necessarily
12// corresponding) index. The memory beyond the slice length is ignored.
13func AnyOverlap(x, y []byte) bool {
14	return len(x) > 0 && len(y) > 0 &&
15		uintptr(unsafe.Pointer(&x[0])) <= uintptr(unsafe.Pointer(&y[len(y)-1])) &&
16		uintptr(unsafe.Pointer(&y[0])) <= uintptr(unsafe.Pointer(&x[len(x)-1]))
17}
18
19// InexactOverlap reports whether x and y share memory at any non-corresponding
20// index. The memory beyond the slice length is ignored. Note that x and y can
21// have different lengths and still not have any inexact overlap.
22//
23// InexactOverlap can be used to implement the requirements of the crypto/cipher
24// AEAD, Block, BlockMode and Stream interfaces.
25func InexactOverlap(x, y []byte) bool {
26	if len(x) == 0 || len(y) == 0 || &x[0] == &y[0] {
27		return false
28	}
29	return AnyOverlap(x, y)
30}
31