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 appengine
6
7// Package subtle implements functions that are often useful in cryptographic
8// code but require careful thought to use correctly.
9//
10// This is a mirror of golang.org/x/crypto/internal/subtle.
11package subtle // import "crypto/internal/subtle"
12
13// This is the Google App Engine standard variant based on reflect
14// because the unsafe package and cgo are disallowed.
15
16import "reflect"
17
18// AnyOverlap reports whether x and y share memory at any (not necessarily
19// corresponding) index. The memory beyond the slice length is ignored.
20func AnyOverlap(x, y []byte) bool {
21	return len(x) > 0 && len(y) > 0 &&
22		reflect.ValueOf(&x[0]).Pointer() <= reflect.ValueOf(&y[len(y)-1]).Pointer() &&
23		reflect.ValueOf(&y[0]).Pointer() <= reflect.ValueOf(&x[len(x)-1]).Pointer()
24}
25
26// InexactOverlap reports whether x and y share memory at any non-corresponding
27// index. The memory beyond the slice length is ignored. Note that x and y can
28// have different lengths and still not have any inexact overlap.
29//
30// InexactOverlap can be used to implement the requirements of the crypto/cipher
31// AEAD, Block, BlockMode and Stream interfaces.
32func InexactOverlap(x, y []byte) bool {
33	if len(x) == 0 || len(y) == 0 || &x[0] == &y[0] {
34		return false
35	}
36	return AnyOverlap(x, y)
37}
38