hash/crc64: Use slicing by 8.

Similar to crc32 slicing by 8.
This also fixes a Crc64KB benchmark actually using 1024 bytes.

Crc64/ISO64KB-4       147µs ± 0%      37µs ± 0%   -75.05%  (p=0.000 n=18+18)
Crc64/ISO4KB-4       9.19µs ± 0%    2.33µs ± 0%   -74.70%  (p=0.000 n=19+20)
Crc64/ISO1KB-4       2.31µs ± 0%    0.60µs ± 0%   -73.81%  (p=0.000 n=19+15)
Crc64/ECMA64KB-4      147µs ± 0%      37µs ± 0%   -75.05%  (p=0.000 n=20+20)
Crc64/Random64KB-4    147µs ± 0%      41µs ± 0%   -72.17%  (p=0.000 n=20+18)
Crc64/Random16KB-4   36.7µs ± 0%    36.5µs ± 0%    -0.54%  (p=0.000 n=18+19)

name                old speed     new speed      delta
Crc64/ISO64KB-4     446MB/s ± 0%  1788MB/s ± 0%  +300.72%  (p=0.000 n=18+18)
Crc64/ISO4KB-4      446MB/s ± 0%  1761MB/s ± 0%  +295.20%  (p=0.000 n=18+20)
Crc64/ISO1KB-4      444MB/s ± 0%  1694MB/s ± 0%  +281.46%  (p=0.000 n=19+20)
Crc64/ECMA64KB-4    446MB/s ± 0%  1788MB/s ± 0%  +300.77%  (p=0.000 n=20+20)
Crc64/Random64KB-4  446MB/s ± 0%  1603MB/s ± 0%  +259.32%  (p=0.000 n=20+18)
Crc64/Random16KB-4  446MB/s ± 0%   448MB/s ± 0%    +0.54%  (p=0.000 n=18+20)

Change-Id: I1c7621d836c486d6bfc41dbe1ec2ff9ab11aedfc
Reviewed-on: https://go-review.googlesource.com/22222
Run-TryBot: Ilya Tocar <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Russ Cox <[email protected]>

src/hash/crc64/crc64.go

@@ -24,9 +24,25 @@ const (
 // Table is a 256-word table representing the polynomial for efficient processing.
 type Table [256]uint64
 
+var (
+	slicing8TableISO  = makeSlicingBy8Table(makeTable(ISO))
+	slicing8TableECMA = makeSlicingBy8Table(makeTable(ECMA))
+)
+
 // MakeTable returns a Table constructed from the specified polynomial.
 // The contents of this Table must not be modified.
 func MakeTable(poly uint64) *Table {
+	switch poly {
+	case ISO:
+		return &slicing8TableISO[0]
+	case ECMA:
+		return &slicing8TableECMA[0]
+	default:
+		return makeTable(poly)
+	}
+}
+
+func makeTable(poly uint64) *Table {
 	t := new(Table)
 	for i := 0; i < 256; i++ {
 		crc := uint64(i)
@@ -42,6 +58,19 @@ func MakeTable(poly uint64) *Table {
 	return t
 }
 
+func makeSlicingBy8Table(t *Table) *[8]Table {
+	var helperTable [8]Table
+	helperTable[0] = *t
+	for i := 0; i < 256; i++ {
+		crc := t[i]
+		for j := 1; j < 8; j++ {
+			crc = t[crc&0xff] ^ (crc >> 8)
+			helperTable[j][i] = crc
+		}
+	}
+	return &helperTable
+}
+
 // digest represents the partial evaluation of a checksum.
 type digest struct {
 	crc uint64
@@ -61,6 +90,35 @@ func (d *digest) Reset() { d.crc = 0 }
 
 func update(crc uint64, tab *Table, p []byte) uint64 {
 	crc = ^crc
+	// Table comparison is somewhat expensive, so avoid it for small sizes
+	for len(p) >= 64 {
+		var helperTable *[8]Table
+		if *tab == slicing8TableECMA[0] {
+			helperTable = slicing8TableECMA
+		} else if *tab == slicing8TableISO[0] {
+			helperTable = slicing8TableISO
+			// For smaller sizes creating extended table takes too much time
+		} else if len(p) > 16384 {
+			helperTable = makeSlicingBy8Table(tab)
+		} else {
+			break
+		}
+		// Update using slicing-by-8
+		for len(p) > 8 {
+			crc ^= uint64(p[0]) | uint64(p[1])<<8 | uint64(p[2])<<16 | uint64(p[3])<<24 |
+				uint64(p[4])<<32 | uint64(p[5])<<40 | uint64(p[6])<<48 | uint64(p[7])<<56
+			crc = helperTable[7][crc&0xff] ^
+				helperTable[6][(crc>>8)&0xff] ^
+				helperTable[5][(crc>>16)&0xff] ^
+				helperTable[4][(crc>>24)&0xff] ^
+				helperTable[3][(crc>>32)&0xff] ^
+				helperTable[2][(crc>>40)&0xff] ^
+				helperTable[1][(crc>>48)&0xff] ^
+				helperTable[0][crc>>56]
+			p = p[8:]
+		}
+	}
+	// For reminders or small sizes
 	for _, v := range p {
 		crc = tab[byte(crc)^v] ^ (crc >> 8)
 	}

src/hash/crc64/crc64_test.go

@@ -72,13 +72,13 @@ func TestGolden(t *testing.T) {
 	}
 }
 
-func BenchmarkISOCrc64KB(b *testing.B) {
-	b.SetBytes(1024)
-	data := make([]byte, 1024)
+func bench(b *testing.B, poly uint64, size int64) {
+	b.SetBytes(size)
+	data := make([]byte, size)
 	for i := range data {
 		data[i] = byte(i)
 	}
-	h := New(MakeTable(ISO))
+	h := New(MakeTable(poly))
 	in := make([]byte, 0, h.Size())
 
 	b.ResetTimer()
@@ -88,3 +88,24 @@ func BenchmarkISOCrc64KB(b *testing.B) {
 		h.Sum(in)
 	}
 }
+
+func BenchmarkCrc64(b *testing.B) {
+	b.Run("ISO64KB", func(b *testing.B) {
+		bench(b, ISO, 64<<10)
+	})
+	b.Run("ISO4KB", func(b *testing.B) {
+		bench(b, ISO, 4<<10)
+	})
+	b.Run("ISO1KB", func(b *testing.B) {
+		bench(b, ISO, 1<<10)
+	})
+	b.Run("ECMA64KB", func(b *testing.B) {
+		bench(b, ECMA, 64<<10)
+	})
+	b.Run("Random64KB", func(b *testing.B) {
+		bench(b, 0x777, 64<<10)
+	})
+	b.Run("Random16KB", func(b *testing.B) {
+		bench(b, 0x777, 16<<10)
+	})
+}