231 lines
6.9 KiB
Go
231 lines
6.9 KiB
Go
// Copyright 2011 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,!gccgo
|
|
|
|
// AMD64-specific hardware-assisted CRC32 algorithms. See crc32.go for a
|
|
// description of the interface that each architecture-specific file
|
|
// implements.
|
|
|
|
package crc32
|
|
|
|
import "unsafe"
|
|
|
|
// This file contains the code to call the SSE 4.2 version of the Castagnoli
|
|
// and IEEE CRC.
|
|
|
|
// haveSSE41/haveSSE42/haveCLMUL are defined in crc_amd64.s and use
|
|
// CPUID to test for SSE 4.1, 4.2 and CLMUL support.
|
|
func haveSSE41() bool
|
|
func haveSSE42() bool
|
|
func haveCLMUL() bool
|
|
|
|
// castagnoliSSE42 is defined in crc32_amd64.s and uses the SSE4.2 CRC32
|
|
// instruction.
|
|
//go:noescape
|
|
func castagnoliSSE42(crc uint32, p []byte) uint32
|
|
|
|
// castagnoliSSE42Triple is defined in crc32_amd64.s and uses the SSE4.2 CRC32
|
|
// instruction.
|
|
//go:noescape
|
|
func castagnoliSSE42Triple(
|
|
crcA, crcB, crcC uint32,
|
|
a, b, c []byte,
|
|
rounds uint32,
|
|
) (retA uint32, retB uint32, retC uint32)
|
|
|
|
// ieeeCLMUL is defined in crc_amd64.s and uses the PCLMULQDQ
|
|
// instruction as well as SSE 4.1.
|
|
//go:noescape
|
|
func ieeeCLMUL(crc uint32, p []byte) uint32
|
|
|
|
var sse42 = haveSSE42()
|
|
var useFastIEEE = haveCLMUL() && haveSSE41()
|
|
|
|
const castagnoliK1 = 168
|
|
const castagnoliK2 = 1344
|
|
|
|
type sse42Table [4]Table
|
|
|
|
var castagnoliSSE42TableK1 *sse42Table
|
|
var castagnoliSSE42TableK2 *sse42Table
|
|
|
|
func archAvailableCastagnoli() bool {
|
|
return sse42
|
|
}
|
|
|
|
func archInitCastagnoli() {
|
|
if !sse42 {
|
|
panic("arch-specific Castagnoli not available")
|
|
}
|
|
castagnoliSSE42TableK1 = new(sse42Table)
|
|
castagnoliSSE42TableK2 = new(sse42Table)
|
|
// See description in updateCastagnoli.
|
|
// t[0][i] = CRC(i000, O)
|
|
// t[1][i] = CRC(0i00, O)
|
|
// t[2][i] = CRC(00i0, O)
|
|
// t[3][i] = CRC(000i, O)
|
|
// where O is a sequence of K zeros.
|
|
var tmp [castagnoliK2]byte
|
|
for b := 0; b < 4; b++ {
|
|
for i := 0; i < 256; i++ {
|
|
val := uint32(i) << uint32(b*8)
|
|
castagnoliSSE42TableK1[b][i] = castagnoliSSE42(val, tmp[:castagnoliK1])
|
|
castagnoliSSE42TableK2[b][i] = castagnoliSSE42(val, tmp[:])
|
|
}
|
|
}
|
|
}
|
|
|
|
// castagnoliShift computes the CRC32-C of K1 or K2 zeroes (depending on the
|
|
// table given) with the given initial crc value. This corresponds to
|
|
// CRC(crc, O) in the description in updateCastagnoli.
|
|
func castagnoliShift(table *sse42Table, crc uint32) uint32 {
|
|
return table[3][crc>>24] ^
|
|
table[2][(crc>>16)&0xFF] ^
|
|
table[1][(crc>>8)&0xFF] ^
|
|
table[0][crc&0xFF]
|
|
}
|
|
|
|
func archUpdateCastagnoli(crc uint32, p []byte) uint32 {
|
|
if !sse42 {
|
|
panic("not available")
|
|
}
|
|
|
|
// This method is inspired from the algorithm in Intel's white paper:
|
|
// "Fast CRC Computation for iSCSI Polynomial Using CRC32 Instruction"
|
|
// The same strategy of splitting the buffer in three is used but the
|
|
// combining calculation is different; the complete derivation is explained
|
|
// below.
|
|
//
|
|
// -- The basic idea --
|
|
//
|
|
// The CRC32 instruction (available in SSE4.2) can process 8 bytes at a
|
|
// time. In recent Intel architectures the instruction takes 3 cycles;
|
|
// however the processor can pipeline up to three instructions if they
|
|
// don't depend on each other.
|
|
//
|
|
// Roughly this means that we can process three buffers in about the same
|
|
// time we can process one buffer.
|
|
//
|
|
// The idea is then to split the buffer in three, CRC the three pieces
|
|
// separately and then combine the results.
|
|
//
|
|
// Combining the results requires precomputed tables, so we must choose a
|
|
// fixed buffer length to optimize. The longer the length, the faster; but
|
|
// only buffers longer than this length will use the optimization. We choose
|
|
// two cutoffs and compute tables for both:
|
|
// - one around 512: 168*3=504
|
|
// - one around 4KB: 1344*3=4032
|
|
//
|
|
// -- The nitty gritty --
|
|
//
|
|
// Let CRC(I, X) be the non-inverted CRC32-C of the sequence X (with
|
|
// initial non-inverted CRC I). This function has the following properties:
|
|
// (a) CRC(I, AB) = CRC(CRC(I, A), B)
|
|
// (b) CRC(I, A xor B) = CRC(I, A) xor CRC(0, B)
|
|
//
|
|
// Say we want to compute CRC(I, ABC) where A, B, C are three sequences of
|
|
// K bytes each, where K is a fixed constant. Let O be the sequence of K zero
|
|
// bytes.
|
|
//
|
|
// CRC(I, ABC) = CRC(I, ABO xor C)
|
|
// = CRC(I, ABO) xor CRC(0, C)
|
|
// = CRC(CRC(I, AB), O) xor CRC(0, C)
|
|
// = CRC(CRC(I, AO xor B), O) xor CRC(0, C)
|
|
// = CRC(CRC(I, AO) xor CRC(0, B), O) xor CRC(0, C)
|
|
// = CRC(CRC(CRC(I, A), O) xor CRC(0, B), O) xor CRC(0, C)
|
|
//
|
|
// The castagnoliSSE42Triple function can compute CRC(I, A), CRC(0, B),
|
|
// and CRC(0, C) efficiently. We just need to find a way to quickly compute
|
|
// CRC(uvwx, O) given a 4-byte initial value uvwx. We can precompute these
|
|
// values; since we can't have a 32-bit table, we break it up into four
|
|
// 8-bit tables:
|
|
//
|
|
// CRC(uvwx, O) = CRC(u000, O) xor
|
|
// CRC(0v00, O) xor
|
|
// CRC(00w0, O) xor
|
|
// CRC(000x, O)
|
|
//
|
|
// We can compute tables corresponding to the four terms for all 8-bit
|
|
// values.
|
|
|
|
crc = ^crc
|
|
|
|
// If a buffer is long enough to use the optimization, process the first few
|
|
// bytes to align the buffer to an 8 byte boundary (if necessary).
|
|
if len(p) >= castagnoliK1*3 {
|
|
delta := int(uintptr(unsafe.Pointer(&p[0])) & 7)
|
|
if delta != 0 {
|
|
delta = 8 - delta
|
|
crc = castagnoliSSE42(crc, p[:delta])
|
|
p = p[delta:]
|
|
}
|
|
}
|
|
|
|
// Process 3*K2 at a time.
|
|
for len(p) >= castagnoliK2*3 {
|
|
// Compute CRC(I, A), CRC(0, B), and CRC(0, C).
|
|
crcA, crcB, crcC := castagnoliSSE42Triple(
|
|
crc, 0, 0,
|
|
p, p[castagnoliK2:], p[castagnoliK2*2:],
|
|
castagnoliK2/24)
|
|
|
|
// CRC(I, AB) = CRC(CRC(I, A), O) xor CRC(0, B)
|
|
crcAB := castagnoliShift(castagnoliSSE42TableK2, crcA) ^ crcB
|
|
// CRC(I, ABC) = CRC(CRC(I, AB), O) xor CRC(0, C)
|
|
crc = castagnoliShift(castagnoliSSE42TableK2, crcAB) ^ crcC
|
|
p = p[castagnoliK2*3:]
|
|
}
|
|
|
|
// Process 3*K1 at a time.
|
|
for len(p) >= castagnoliK1*3 {
|
|
// Compute CRC(I, A), CRC(0, B), and CRC(0, C).
|
|
crcA, crcB, crcC := castagnoliSSE42Triple(
|
|
crc, 0, 0,
|
|
p, p[castagnoliK1:], p[castagnoliK1*2:],
|
|
castagnoliK1/24)
|
|
|
|
// CRC(I, AB) = CRC(CRC(I, A), O) xor CRC(0, B)
|
|
crcAB := castagnoliShift(castagnoliSSE42TableK1, crcA) ^ crcB
|
|
// CRC(I, ABC) = CRC(CRC(I, AB), O) xor CRC(0, C)
|
|
crc = castagnoliShift(castagnoliSSE42TableK1, crcAB) ^ crcC
|
|
p = p[castagnoliK1*3:]
|
|
}
|
|
|
|
// Use the simple implementation for what's left.
|
|
crc = castagnoliSSE42(crc, p)
|
|
return ^crc
|
|
}
|
|
|
|
func archAvailableIEEE() bool {
|
|
return useFastIEEE
|
|
}
|
|
|
|
var archIeeeTable8 *slicing8Table
|
|
|
|
func archInitIEEE() {
|
|
if !useFastIEEE {
|
|
panic("not available")
|
|
}
|
|
// We still use slicing-by-8 for small buffers.
|
|
archIeeeTable8 = slicingMakeTable(IEEE)
|
|
}
|
|
|
|
func archUpdateIEEE(crc uint32, p []byte) uint32 {
|
|
if !useFastIEEE {
|
|
panic("not available")
|
|
}
|
|
|
|
if len(p) >= 64 {
|
|
left := len(p) & 15
|
|
do := len(p) - left
|
|
crc = ^ieeeCLMUL(^crc, p[:do])
|
|
p = p[do:]
|
|
}
|
|
if len(p) == 0 {
|
|
return crc
|
|
}
|
|
return slicingUpdate(crc, archIeeeTable8, p)
|
|
}
|