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43 lines
1.2 KiB
Go
43 lines
1.2 KiB
Go
// Copyright 2018 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found src the LICENSE file.
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package chacha20
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import "runtime"
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// Platforms that have fast unaligned 32-bit little endian accesses.
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const unaligned = runtime.GOARCH == "386" ||
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runtime.GOARCH == "amd64" ||
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runtime.GOARCH == "arm64" ||
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runtime.GOARCH == "ppc64le" ||
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runtime.GOARCH == "s390x"
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// addXor reads a little endian uint32 from src, XORs it with (a + b) and
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// places the result in little endian byte order in dst.
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func addXor(dst, src []byte, a, b uint32) {
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_, _ = src[3], dst[3] // bounds check elimination hint
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if unaligned {
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// The compiler should optimize this code into
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// 32-bit unaligned little endian loads and stores.
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// TODO: delete once the compiler does a reliably
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// good job with the generic code below.
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// See issue #25111 for more details.
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v := uint32(src[0])
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v |= uint32(src[1]) << 8
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v |= uint32(src[2]) << 16
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v |= uint32(src[3]) << 24
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v ^= a + b
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dst[0] = byte(v)
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dst[1] = byte(v >> 8)
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dst[2] = byte(v >> 16)
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dst[3] = byte(v >> 24)
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} else {
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a += b
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dst[0] = src[0] ^ byte(a)
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dst[1] = src[1] ^ byte(a>>8)
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dst[2] = src[2] ^ byte(a>>16)
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dst[3] = src[3] ^ byte(a>>24)
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}
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}
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