package crc32
+import "unsafe"
+
// This file contains the code to call the SSE 4.2 version of the Castagnoli
// and IEEE CRC.
func haveSSE42() bool
func haveCLMUL() bool
-// castagnoliSSE42 is defined in crc_amd64.s and uses the SSE4.2 CRC32
+// 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
var sse42 = haveSSE42()
var useFastIEEE = haveCLMUL() && haveSSE41()
+const castagnoliK1 = 168
+const castagnoliK2 = 1344
+
+type sse42Table [4]Table
+
+var castagnoliSSE42TableK1 *sse42Table
+var castagnoliSSE42TableK2 *sse42Table
+
+func castagnoliInitArch() (needGenericTables bool) {
+ if !sse42 {
+ return true
+ }
+ 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[:])
+ }
+ }
+ return false
+}
+
+// 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 updateCastagnoli(crc uint32, p []byte) uint32 {
- if sse42 {
- return castagnoliSSE42(crc, p)
+ if !sse42 {
+ // Use slicing-by-8 on larger inputs.
+ if len(p) >= sliceBy8Cutoff {
+ return updateSlicingBy8(crc, castagnoliTable8, p)
+ }
+ return update(crc, castagnoliTable, p)
}
- // Use slicing-by-8 on larger inputs.
- if len(p) >= sliceBy8Cutoff {
- return updateSlicingBy8(crc, castagnoliTable8, p)
+
+ // 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:]
+ }
}
- return update(crc, castagnoliTable, p)
+
+ // 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 updateIEEE(crc uint32, p []byte) uint32 {
import (
"hash"
"io"
+ "math/rand"
"testing"
)
}
}
+func TestCastagnoliSSE42(t *testing.T) {
+ if !sse42 {
+ t.Skip("SSE42 not supported")
+ }
+
+ // Init the SSE42 tables.
+ MakeTable(Castagnoli)
+
+ // Manually init the software implementation to compare against.
+ castagnoliTable = makeTable(Castagnoli)
+ castagnoliTable8 = makeTable8(Castagnoli)
+
+ // The optimized SSE4.2 implementation behaves differently for different
+ // lengths (especially around multiples of K*3). Crosscheck against the
+ // software implementation for various lengths.
+ for _, base := range []int{castagnoliK1, castagnoliK2, castagnoliK1 + castagnoliK2} {
+ for _, baseMult := range []int{2, 3, 5, 6, 9, 30} {
+ for _, variation := range []int{0, 1, 2, 3, 4, 7, 10, 16, 32, 50, 128} {
+ for _, varMult := range []int{-2, -1, +1, +2} {
+ length := base*baseMult + variation*varMult
+ p := make([]byte, length)
+ _, _ = rand.Read(p)
+ crcInit := uint32(rand.Int63())
+ correct := updateSlicingBy8(crcInit, castagnoliTable8, p)
+ result := updateCastagnoli(crcInit, p)
+ if result != correct {
+ t.Errorf("SSE42 implementation = 0x%x want 0x%x (buffer length %d)",
+ result, correct, len(p))
+ }
+ }
+ }
+ }
+ }
+}
+
func BenchmarkIEEECrc40B(b *testing.B) {
benchmark(b, NewIEEE(), 40, 0)
}
benchmark(b, New(MakeTable(Castagnoli)), 40, 0)
}
+func BenchmarkCastagnoliCrc40BMisaligned(b *testing.B) {
+ benchmark(b, New(MakeTable(Castagnoli)), 40, 1)
+}
+
+func BenchmarkCastagnoliCrc512(b *testing.B) {
+ benchmark(b, New(MakeTable(Castagnoli)), 512, 0)
+}
+
+func BenchmarkCastagnoliCrc512Misaligned(b *testing.B) {
+ benchmark(b, New(MakeTable(Castagnoli)), 512, 1)
+}
+
func BenchmarkCastagnoliCrc1KB(b *testing.B) {
benchmark(b, New(MakeTable(Castagnoli)), 1<<10, 0)
}
+func BenchmarkCastagnoliCrc1KBMisaligned(b *testing.B) {
+ benchmark(b, New(MakeTable(Castagnoli)), 1<<10, 1)
+}
+
func BenchmarkCastagnoliCrc4KB(b *testing.B) {
benchmark(b, New(MakeTable(Castagnoli)), 4<<10, 0)
}
+func BenchmarkCastagnoliCrc4KBMisaligned(b *testing.B) {
+ benchmark(b, New(MakeTable(Castagnoli)), 4<<10, 1)
+}
+
func BenchmarkCastagnoliCrc32KB(b *testing.B) {
benchmark(b, New(MakeTable(Castagnoli)), 32<<10, 0)
}
+func BenchmarkCastagnoliCrc32KBMisaligned(b *testing.B) {
+ benchmark(b, New(MakeTable(Castagnoli)), 32<<10, 1)
+}
+
func benchmark(b *testing.B, h hash.Hash32, n, alignment int64) {
b.SetBytes(n)
data := make([]byte, n+alignment)