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//go:build purego
 6
 7// Package alias implements memory aliasing tests.
 8package alias
 9
10// This is the Google App Engine standard variant based on reflect
11// because the unsafe package and cgo are disallowed.
12
13import "reflect"
14
15// AnyOverlap reports whether x and y share memory at any (not necessarily
16// corresponding) index. The memory beyond the slice length is ignored.
17func AnyOverlap(x, y []byte) bool {
18	return len(x) > 0 && len(y) > 0 &&
19		reflect.ValueOf(&x[0]).Pointer() <= reflect.ValueOf(&y[len(y)-1]).Pointer() &&
20		reflect.ValueOf(&y[0]).Pointer() <= reflect.ValueOf(&x[len(x)-1]).Pointer()
21}
22
23// InexactOverlap reports whether x and y share memory at any non-corresponding
24// index. The memory beyond the slice length is ignored. Note that x and y can
25// have different lengths and still not have any inexact overlap.
26//
27// InexactOverlap can be used to implement the requirements of the crypto/cipher
28// AEAD, Block, BlockMode and Stream interfaces.
29func InexactOverlap(x, y []byte) bool {
30	if len(x) == 0 || len(y) == 0 || &x[0] == &y[0] {
31		return false
32	}
33	return AnyOverlap(x, y)
34}