libgo/go/crypto/internal/subtle/aliasing.go

   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 //
  10 // This is a mirror of golang.org/x/crypto/internal/subtle.
  11 package subtle // import "crypto/internal/subtle"
  12
  13 import "unsafe"
  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.
  17 func AnyOverlap(x, y []byte) bool {
  18         return len(x) > 0 && len(y) > 0 &&
  19                 uintptr(unsafe.Pointer(&x[0])) <= uintptr(unsafe.Pointer(&y[len(y)-1])) &&
  20                 uintptr(unsafe.Pointer(&y[0])) <= uintptr(unsafe.Pointer(&x[len(x)-1]))
  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.
  29 func 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 }