56 lines
2.0 KiB
Go
56 lines
2.0 KiB
Go
// Copyright 2012 Aaron Jacobs. All Rights Reserved.
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// Author: aaronjjacobs@gmail.com (Aaron Jacobs)
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// +build amd64 arm64 ppc64 ppc64le s390x mips64 mips64le
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// This code assumes that it's safe to perform unaligned word-sized loads. This is safe on:
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// - arm64 per http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0024a/ch05s01s02.html
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// - Section "5.5.8 Alignment Interrupt" of PowerPC Operating Environment Architecture Book III Version 2.02
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// (the first PowerPC ISA version to include 64-bit), available from
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// http://www.ibm.com/developerworks/systems/library/es-archguide-v2.html does not permit fixed-point loads
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// or stores to generate exceptions on unaligned access
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// - IBM mainframe's have allowed unaligned accesses since the System/370 arrived in 1970
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// - On mips unaligned accesses are fixed up by the kernel per https://www.linux-mips.org/wiki/Alignment
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// so performance might be quite bad but it will work.
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package cmac
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import (
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"log"
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"unsafe"
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)
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// XOR the blockSize bytes starting at a and b, writing the result over dst.
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func xorBlock(
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dstPtr unsafe.Pointer,
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aPtr unsafe.Pointer,
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bPtr unsafe.Pointer) {
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// Check assumptions. (These are compile-time constants, so this should
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// compile out.)
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const wordSize = unsafe.Sizeof(uintptr(0))
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if blockSize != 2*wordSize {
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log.Panicf("%d %d", blockSize, wordSize)
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}
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// Convert.
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a := (*[2]uintptr)(aPtr)
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b := (*[2]uintptr)(bPtr)
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dst := (*[2]uintptr)(dstPtr)
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// Compute.
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dst[0] = a[0] ^ b[0]
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dst[1] = a[1] ^ b[1]
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}
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