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