Preparing move to modules

[govpn.git] / internal / subtle / aliasing_appengine.go

diff --git a/internal/subtle/aliasing_appengine.go b/internal/subtle/aliasing_appengine.go
new file mode 100644 (file)
index 0000000..0cc4a8a
--- /dev/null
+++ b/internal/subtle/aliasing_appengine.go
@@ -0,0 +1,35 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build appengine
+
+// Package subtle implements functions that are often useful in cryptographic
+// code but require careful thought to use correctly.
+package subtle // import "golang.org/x/crypto/internal/subtle"
+
+// This is the Google App Engine standard variant based on reflect
+// because the unsafe package and cgo are disallowed.
+
+import "reflect"
+
+// AnyOverlap reports whether x and y share memory at any (not necessarily
+// corresponding) index. The memory beyond the slice length is ignored.
+func AnyOverlap(x, y []byte) bool {
+       return len(x) > 0 && len(y) > 0 &&
+               reflect.ValueOf(&x[0]).Pointer() <= reflect.ValueOf(&y[len(y)-1]).Pointer() &&
+               reflect.ValueOf(&y[0]).Pointer() <= reflect.ValueOf(&x[len(x)-1]).Pointer()
+}
+
+// InexactOverlap reports whether x and y share memory at any non-corresponding
+// index. The memory beyond the slice length is ignored. Note that x and y can
+// have different lengths and still not have any inexact overlap.
+//
+// InexactOverlap can be used to implement the requirements of the crypto/cipher
+// AEAD, Block, BlockMode and Stream interfaces.
+func InexactOverlap(x, y []byte) bool {
+       if len(x) == 0 || len(y) == 0 || &x[0] == &y[0] {
+               return false
+       }
+       return AnyOverlap(x, y)
+}