alias_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  
     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
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