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