alias_purego.go raw

   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.
   8  package alias
   9  
  10  // This is the Google App Engine standard variant based on reflect
  11  // because the unsafe package and cgo are disallowed.
  12  
  13  import "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.
  17  func 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.
  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  }
  35