hash/crc32: cleanup code and improve tests

Major reorganization of the crc32 code:

 - The arch-specific files now implement a well-defined interface
   (documented in crc32.go). They no longer have the responsibility of
   initializing and falling back to a non-accelerated implementation;
   instead, that happens in the higher level code.

 - The non-accelerated algorithms are moved to a separate file with no
   dependencies on other code.

 - The "cutoff" optimization for slicing-by-8 is moved inside the
   algorithm itself (as opposed to every callsite).

Tests are significantly improved:
 - direct tests for the non-accelerated algorithms.
 - "cross-check" tests for arch-specific implementations (all archs).
 - tests for misaligned buffers for both IEEE and Castagnoli.

Fixes #16909.

Change-Id: I9b6dd83b7a57cd615eae901c0a6d61c6b8091c74
Reviewed-on: https://go-review.googlesource.com/27935Reviewed-by: Keith Randall <khr@golang.org>

src/hash/crc32/crc32.go

@@ -20,9 +20,6 @@ import (
 // The size of a CRC-32 checksum in bytes.
 const Size = 4
 
-// Use "slice by 8" when payload >= this value.
-const sliceBy8Cutoff = 16
-
 // Predefined polynomials.
 const (
 	// IEEE is by far and away the most common CRC-32 polynomial.
@@ -43,80 +40,96 @@ const (
 // Table is a 256-word table representing the polynomial for efficient processing.
 type Table [256]uint32
 
+// This file makes use of functions implemented in architecture-specific files.
+// The interface that they implement is as follows:
+//
+//    // archAvailableIEEE reports whether an architecture-specific CRC32-IEEE
+//    // algorithm is available.
+//    archAvailableIEEE() bool
+//
+//    // archInitIEEE initializes the architecture-specific CRC3-IEEE algorithm.
+//    // It can only be called if archAvailableIEEE() returns true.
+//    archInitIEEE()
+//
+//    // archUpdateIEEE updates the given CRC32-IEEE. It can only be called if
+//    // archInitIEEE() was previously called.
+//    archUpdateIEEE(crc uint32, p []byte) uint32
+//
+//    // archAvailableCastagnoli reports whether an architecture-specific
+//    // CRC32-C algorithm is available.
+//    archAvailableCastagnoli() bool
+//
+//    // archInitCastagnoli initializes the architecture-specific CRC32-C
+//    // algorithm. It can only be called if archAvailableCastagnoli() returns
+//    // true.
+//    archInitCastagnoli()
+//
+//    // archUpdateCastagnoli updates the given CRC32-C. It can only be called
+//    // if archInitCastagnoli() was previously called.
+//    archUpdateCastagnoli(crc uint32, p []byte) uint32
+
 // castagnoliTable points to a lazily initialized Table for the Castagnoli
 // polynomial. MakeTable will always return this value when asked to make a
 // Castagnoli table so we can compare against it to find when the caller is
 // using this polynomial.
 var castagnoliTable *Table
 var castagnoliTable8 *slicing8Table
+var castagnoliArchImpl bool
+var updateCastagnoli func(crc uint32, p []byte) uint32
 var castagnoliOnce sync.Once
 
 func castagnoliInit() {
-	// Call the arch-specific init function and let it decide if we will need
-	// the tables for the generic implementation.
-	needGenericTables := castagnoliInitArch()
-
-	if needGenericTables {
-		castagnoliTable8 = makeTable8(Castagnoli)
+	castagnoliTable = simpleMakeTable(Castagnoli)
+	castagnoliArchImpl = archAvailableCastagnoli()
+
+	if castagnoliArchImpl {
+		archInitCastagnoli()
+		updateCastagnoli = archUpdateCastagnoli
+	} else {
+		// Initialize the slicing-by-8 table.
+		castagnoliTable8 = slicingMakeTable(Castagnoli)
+		updateCastagnoli = func(crc uint32, p []byte) uint32 {
+			return slicingUpdate(crc, castagnoliTable8, p)
+		}
 	}
-
-	// Even if we don't need the contents of this table, we use it as a handle
-	// returned by MakeTable. We should find a way to clean this up (see #16909).
-	castagnoliTable = makeTable(Castagnoli)
 }
 
 // IEEETable is the table for the IEEE polynomial.
-var IEEETable = makeTable(IEEE)
-
-// slicing8Table is array of 8 Tables
-type slicing8Table [8]Table
+var IEEETable = simpleMakeTable(IEEE)
 
 // ieeeTable8 is the slicing8Table for IEEE
 var ieeeTable8 *slicing8Table
-var ieeeTable8Once sync.Once
+var ieeeArchImpl bool
+var updateIEEE func(crc uint32, p []byte) uint32
+var ieeeOnce sync.Once
+
+func ieeeInit() {
+	ieeeArchImpl = archAvailableIEEE()
+
+	if ieeeArchImpl {
+		archInitIEEE()
+		updateIEEE = archUpdateIEEE
+	} else {
+		// Initialize the slicing-by-8 table.
+		ieeeTable8 = slicingMakeTable(IEEE)
+		updateIEEE = func(crc uint32, p []byte) uint32 {
+			return slicingUpdate(crc, ieeeTable8, p)
+		}
+	}
+}
 
 // MakeTable returns a Table constructed from the specified polynomial.
 // The contents of this Table must not be modified.
 func MakeTable(poly uint32) *Table {
 	switch poly {
 	case IEEE:
+		ieeeOnce.Do(ieeeInit)
 		return IEEETable
 	case Castagnoli:
 		castagnoliOnce.Do(castagnoliInit)
 		return castagnoliTable
 	}
-	return makeTable(poly)
-}
-
-// makeTable returns the Table constructed from the specified polynomial.
-func makeTable(poly uint32) *Table {
-	t := new(Table)
-	for i := 0; i < 256; i++ {
-		crc := uint32(i)
-		for j := 0; j < 8; j++ {
-			if crc&1 == 1 {
-				crc = (crc >> 1) ^ poly
-			} else {
-				crc >>= 1
-			}
-		}
-		t[i] = crc
-	}
-	return t
-}
-
-// makeTable8 returns slicing8Table constructed from the specified polynomial.
-func makeTable8(poly uint32) *slicing8Table {
-	t := new(slicing8Table)
-	t[0] = *makeTable(poly)
-	for i := 0; i < 256; i++ {
-		crc := t[0][i]
-		for j := 1; j < 8; j++ {
-			crc = t[0][crc&0xFF] ^ (crc >> 8)
-			t[j][i] = crc
-		}
-	}
-	return t
+	return simpleMakeTable(poly)
 }
 
 // digest represents the partial evaluation of a checksum.
@@ -128,7 +141,12 @@ type digest struct {
 // New creates a new hash.Hash32 computing the CRC-32 checksum
 // using the polynomial represented by the Table.
 // Its Sum method will lay the value out in big-endian byte order.
-func New(tab *Table) hash.Hash32 { return &digest{0, tab} }
+func New(tab *Table) hash.Hash32 {
+	if tab == IEEETable {
+		ieeeOnce.Do(ieeeInit)
+	}
+	return &digest{0, tab}
+}
 
 // NewIEEE creates a new hash.Hash32 computing the CRC-32 checksum
 // using the IEEE polynomial.
@@ -141,44 +159,32 @@ func (d *digest) BlockSize() int { return 1 }
 
 func (d *digest) Reset() { d.crc = 0 }
 
-func update(crc uint32, tab *Table, p []byte) uint32 {
-	crc = ^crc
-	for _, v := range p {
-		crc = tab[byte(crc)^v] ^ (crc >> 8)
-	}
-	return ^crc
-}
-
-// updateSlicingBy8 updates CRC using Slicing-by-8
-func updateSlicingBy8(crc uint32, tab *slicing8Table, p []byte) uint32 {
-	crc = ^crc
-	for len(p) > 8 {
-		crc ^= uint32(p[0]) | uint32(p[1])<<8 | uint32(p[2])<<16 | uint32(p[3])<<24
-		crc = tab[0][p[7]] ^ tab[1][p[6]] ^ tab[2][p[5]] ^ tab[3][p[4]] ^
-			tab[4][crc>>24] ^ tab[5][(crc>>16)&0xFF] ^
-			tab[6][(crc>>8)&0xFF] ^ tab[7][crc&0xFF]
-		p = p[8:]
-	}
-	crc = ^crc
-	if len(p) == 0 {
-		return crc
-	}
-	return update(crc, &tab[0], p)
-}
-
 // Update returns the result of adding the bytes in p to the crc.
 func Update(crc uint32, tab *Table, p []byte) uint32 {
 	switch tab {
 	case castagnoliTable:
 		return updateCastagnoli(crc, p)
 	case IEEETable:
+		// Unfortunately, because IEEETable is exported, IEEE may be used without a
+		// call to MakeTable. We have to make sure it gets initialized in that case.
+		ieeeOnce.Do(ieeeInit)
 		return updateIEEE(crc, p)
+	default:
+		return simpleUpdate(crc, tab, p)
 	}
-	return update(crc, tab, p)
 }
 
 func (d *digest) Write(p []byte) (n int, err error) {
-	d.crc = Update(d.crc, d.tab, p)
+	switch d.tab {
+	case castagnoliTable:
+		d.crc = updateCastagnoli(d.crc, p)
+	case IEEETable:
+		// We only create digest objects through New() which takes care of
+		// initialization in this case.
+		d.crc = updateIEEE(d.crc, p)
+	default:
+		d.crc = simpleUpdate(d.crc, d.tab, p)
+	}
 	return len(p), nil
 }
 
@@ -195,4 +201,7 @@ func Checksum(data []byte, tab *Table) uint32 { return Update(0, tab, data) }
 
 // ChecksumIEEE returns the CRC-32 checksum of data
 // using the IEEE polynomial.
-func ChecksumIEEE(data []byte) uint32 { return updateIEEE(0, data) }
+func ChecksumIEEE(data []byte) uint32 {
+	ieeeOnce.Do(ieeeInit)
+	return updateIEEE(0, data)
+}

src/hash/crc32/crc32_amd64.go

@@ -2,6 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// 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"
@@ -45,9 +49,13 @@ type sse42Table [4]Table
 var castagnoliSSE42TableK1 *sse42Table
 var castagnoliSSE42TableK2 *sse42Table
 
-func castagnoliInitArch() (needGenericTables bool) {
+func archAvailableCastagnoli() bool {
+	return sse42
+}
+
+func archInitCastagnoli() {
 	if !sse42 {
-		return true
+		panic("arch-specific Castagnoli not available")
 	}
 	castagnoliSSE42TableK1 = new(sse42Table)
 	castagnoliSSE42TableK2 = new(sse42Table)
@@ -65,7 +73,6 @@ func castagnoliInitArch() (needGenericTables bool) {
 			castagnoliSSE42TableK2[b][i] = castagnoliSSE42(val, tmp[:])
 		}
 	}
-	return false
 }
 
 // castagnoliShift computes the CRC32-C of K1 or K2 zeroes (depending on the
@@ -78,13 +85,9 @@ func castagnoliShift(table *sse42Table, crc uint32) uint32 {
 		table[0][crc&0xFF]
 }
 
-func updateCastagnoli(crc uint32, p []byte) uint32 {
+func archUpdateCastagnoli(crc uint32, p []byte) uint32 {
 	if !sse42 {
-		// Use slicing-by-8 on larger inputs.
-		if len(p) >= sliceBy8Cutoff {
-			return updateSlicingBy8(crc, castagnoliTable8, p)
-		}
-		return update(crc, castagnoliTable, p)
+		panic("not available")
 	}
 
 	// This method is inspired from the algorithm in Intel's white paper:
@@ -193,24 +196,33 @@ func updateCastagnoli(crc uint32, p []byte) uint32 {
 	return ^crc
 }
 
-func updateIEEE(crc uint32, p []byte) uint32 {
-	if useFastIEEE && len(p) >= 64 {
+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])
-		if left > 0 {
-			crc = update(crc, IEEETable, p[do:])
-		}
-		return crc
+		p = p[do:]
 	}
-
-	// Use slicing-by-8 on larger inputs.
-	if len(p) >= sliceBy8Cutoff {
-		ieeeTable8Once.Do(func() {
-			ieeeTable8 = makeTable8(IEEE)
-		})
-		return updateSlicingBy8(crc, ieeeTable8, p)
+	if len(p) == 0 {
+		return crc
 	}
-
-	return update(crc, IEEETable, p)
+	return slicingUpdate(crc, archIeeeTable8, p)
 }

src/hash/crc32/crc32_amd64_test.go

-// Copyright 2009 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.
-
-package crc32
-
-import (
-	"math/rand"
-	"testing"
-)
-
-func TestCastagnoliSSE42(t *testing.T) {
-	if !sse42 {
-		t.Skip("SSE42 not supported")
-	}
-
-	// Init the SSE42 tables.
-	castagnoliOnce.Do(castagnoliInit)
-
-	// Generate a table to use with the non-SSE version.
-	slicingTable := 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, slicingTable, p)
-					result := updateCastagnoli(crcInit, p)
-					if result != correct {
-						t.Errorf("SSE42 implementation = 0x%x want 0x%x (buffer length %d)",
-							result, correct, len(p))
-					}
-				}
-			}
-		}
-	}
-}

src/hash/crc32/crc32_amd64p32.go

@@ -11,37 +11,31 @@ package crc32
 // support.
 func haveSSE42() bool
 
-// castagnoliSSE42 is defined in crc32_amd64.s and uses the SSE4.2 CRC32
+// castagnoliSSE42 is defined in crc32_amd64p32.s and uses the SSE4.2 CRC32
 // instruction.
 //go:noescape
 func castagnoliSSE42(crc uint32, p []byte) uint32
 
 var sse42 = haveSSE42()
 
-func castagnoliInitArch() (needGenericTables bool) {
-	// We only need the generic implementation tables if we don't have SSE4.2.
-	return !sse42
+func archAvailableCastagnoli() bool {
+	return sse42
 }
 
-func updateCastagnoli(crc uint32, p []byte) uint32 {
-	if sse42 {
-		return castagnoliSSE42(crc, p)
+func archInitCastagnoli() {
+	if !sse42 {
+		panic("not available")
 	}
-	// Use slicing-by-8 on larger inputs.
-	if len(p) >= sliceBy8Cutoff {
-		return updateSlicingBy8(crc, castagnoliTable8, p)
-	}
-	return update(crc, castagnoliTable, p)
+	// No initialization necessary.
 }
 
-func updateIEEE(crc uint32, p []byte) uint32 {
-	// Use slicing-by-8 on larger inputs.
-	if len(p) >= sliceBy8Cutoff {
-		ieeeTable8Once.Do(func() {
-			ieeeTable8 = makeTable8(IEEE)
-		})
-		return updateSlicingBy8(crc, ieeeTable8, p)
+func archUpdateCastagnoli(crc uint32, p []byte) uint32 {
+	if !sse42 {
+		panic("not available")
 	}
-
-	return update(crc, IEEETable, p)
+	return castagnoliSSE42(crc, p)
 }
+
+func archAvailableIEEE() bool                    { return false }
+func archInitIEEE()                              { panic("not available") }
+func archUpdateIEEE(crc uint32, p []byte) uint32 { panic("not available") }

src/hash/crc32/crc32_generic.go

@@ -2,32 +2,88 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !amd64,!amd64p32,!s390x
+// This file contains CRC32 algorithms that are not specific to any architecture
+// and don't use hardware acceleration.
+//
+// The simple (and slow) CRC32 implementation only uses a 256*4 bytes table.
+//
+// The slicing-by-8 algorithm is a faster implementation that uses a bigger
+// table (8*256*4 bytes).
 
 package crc32
 
-// This file contains the generic version of updateCastagnoli which does
-// slicing-by-8, or uses the fallback for very small sizes.
+// simpleMakeTable allocates and constructs a Table for the specified
+// polynomial. The table is suitable for use with the simple algorithm
+// (simpleUpdate).
+func simpleMakeTable(poly uint32) *Table {
+	t := new(Table)
+	simplePopulateTable(poly, t)
+	return t
+}
+
+// simplePopulateTable constructs a Table for the specified polynomial, suitable
+// for use with simpleUpdate.
+func simplePopulateTable(poly uint32, t *Table) {
+	for i := 0; i < 256; i++ {
+		crc := uint32(i)
+		for j := 0; j < 8; j++ {
+			if crc&1 == 1 {
+				crc = (crc >> 1) ^ poly
+			} else {
+				crc >>= 1
+			}
+		}
+		t[i] = crc
+	}
+}
 
-func castagnoliInitArch() (needGenericTables bool) {
-	return true
+// simpleUpdate uses the simple algorithm to update the CRC, given a table that
+// was previously computed using simpleMakeTable.
+func simpleUpdate(crc uint32, tab *Table, p []byte) uint32 {
+	crc = ^crc
+	for _, v := range p {
+		crc = tab[byte(crc)^v] ^ (crc >> 8)
+	}
+	return ^crc
 }
 
-func updateCastagnoli(crc uint32, p []byte) uint32 {
-	// Use slicing-by-8 on larger inputs.
-	if len(p) >= sliceBy8Cutoff {
-		return updateSlicingBy8(crc, castagnoliTable8, p)
+// Use slicing-by-8 when payload >= this value.
+const slicing8Cutoff = 16
+
+// slicing8Table is array of 8 Tables, used by the slicing-by-8 algorithm.
+type slicing8Table [8]Table
+
+// slicingMakeTable constructs a slicing8Table for the specified polynomial. The
+// table is suitable for use with the slicing-by-8 algorithm (slicingUpdate).
+func slicingMakeTable(poly uint32) *slicing8Table {
+	t := new(slicing8Table)
+	simplePopulateTable(poly, &t[0])
+	for i := 0; i < 256; i++ {
+		crc := t[0][i]
+		for j := 1; j < 8; j++ {
+			crc = t[0][crc&0xFF] ^ (crc >> 8)
+			t[j][i] = crc
+		}
 	}
-	return update(crc, castagnoliTable, p)
+	return t
 }
 
-func updateIEEE(crc uint32, p []byte) uint32 {
-	// Use slicing-by-8 on larger inputs.
-	if len(p) >= sliceBy8Cutoff {
-		ieeeTable8Once.Do(func() {
-			ieeeTable8 = makeTable8(IEEE)
-		})
-		return updateSlicingBy8(crc, ieeeTable8, p)
+// slicingUpdate uses the slicing-by-8 algorithm to update the CRC, given a
+// table that was previously computed using slicingMakeTable.
+func slicingUpdate(crc uint32, tab *slicing8Table, p []byte) uint32 {
+	if len(p) >= slicing8Cutoff {
+		crc = ^crc
+		for len(p) > 8 {
+			crc ^= uint32(p[0]) | uint32(p[1])<<8 | uint32(p[2])<<16 | uint32(p[3])<<24
+			crc = tab[0][p[7]] ^ tab[1][p[6]] ^ tab[2][p[5]] ^ tab[3][p[4]] ^
+				tab[4][crc>>24] ^ tab[5][(crc>>16)&0xFF] ^
+				tab[6][(crc>>8)&0xFF] ^ tab[7][crc&0xFF]
+			p = p[8:]
+		}
+		crc = ^crc
+	}
+	if len(p) == 0 {
+		return crc
 	}
-	return update(crc, IEEETable, p)
+	return simpleUpdate(crc, &tab[0], p)
 }

src/hash/crc32/crc32_otherarch.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 !amd64,!amd64p32,!s390x
+
+package crc32
+
+func archAvailableIEEE() bool                    { return false }
+func archInitIEEE()                              { panic("not available") }
+func archUpdateIEEE(crc uint32, p []byte) uint32 { panic("not available") }
+
+func archAvailableCastagnoli() bool                    { return false }
+func archInitCastagnoli()                              { panic("not available") }
+func archUpdateCastagnoli(crc uint32, p []byte) uint32 { panic("not available") }

src/hash/crc32/crc32_s390x.go

@@ -25,62 +25,65 @@ func vectorizedCastagnoli(crc uint32, p []byte) uint32
 //go:noescape
 func vectorizedIEEE(crc uint32, p []byte) uint32
 
-func castagnoliInitArch() (needGenericTables bool) {
-	return true
+func archAvailableCastagnoli() bool {
+	return hasVX
 }
 
-func genericCastagnoli(crc uint32, p []byte) uint32 {
-	// Use slicing-by-8 on larger inputs.
-	if len(p) >= sliceBy8Cutoff {
-		return updateSlicingBy8(crc, castagnoliTable8, p)
-	}
-	return update(crc, castagnoliTable, p)
-}
+var archCastagnoliTable8 *slicing8Table
 
-func genericIEEE(crc uint32, p []byte) uint32 {
-	// Use slicing-by-8 on larger inputs.
-	if len(p) >= sliceBy8Cutoff {
-		ieeeTable8Once.Do(func() {
-			ieeeTable8 = makeTable8(IEEE)
-		})
-		return updateSlicingBy8(crc, ieeeTable8, p)
+func archInitCastagnoli() {
+	if !hasVX {
+		panic("not available")
 	}
-	return update(crc, IEEETable, p)
+	// We still use slicing-by-8 for small buffers.
+	archCastagnoliTable8 = slicingMakeTable(Castagnoli)
 }
 
-// updateCastagnoli calculates the checksum of p using
-// vectorizedCastagnoli if possible and falling back onto
-// genericCastagnoli as needed.
-func updateCastagnoli(crc uint32, p []byte) uint32 {
-	// Use vectorized function if vector facility is available and
-	// data length is above threshold.
-	if hasVX && len(p) >= vxMinLen {
+// archUpdateCastagnoli calculates the checksum of p using
+// vectorizedCastagnoli.
+func archUpdateCastagnoli(crc uint32, p []byte) uint32 {
+	if !hasVX {
+		panic("not available")
+	}
+	// Use vectorized function if data length is above threshold.
+	if len(p) >= vxMinLen {
 		aligned := len(p) & ^vxAlignMask
 		crc = vectorizedCastagnoli(crc, p[:aligned])
 		p = p[aligned:]
-		// process remaining data
-		if len(p) > 0 {
-			crc = genericCastagnoli(crc, p)
-		}
+	}
+	if len(p) == 0 {
 		return crc
 	}
-	return genericCastagnoli(crc, p)
+	return slicingUpdate(crc, archCastagnoliTable8, p)
+}
+
+func archAvailableIEEE() bool {
+	return hasVX
+}
+
+var archIeeeTable8 *slicing8Table
+
+func archInitIEEE() {
+	if !hasVX {
+		panic("not available")
+	}
+	// We still use slicing-by-8 for small buffers.
+	archIeeeTable8 = slicingMakeTable(IEEE)
 }
 
-// updateIEEE calculates the checksum of p using vectorizedIEEE if
-// possible and falling back onto genericIEEE as needed.
-func updateIEEE(crc uint32, p []byte) uint32 {
-	// Use vectorized function if vector facility is available and
-	// data length is above threshold.
-	if hasVX && len(p) >= vxMinLen {
+// archUpdateIEEE calculates the checksum of p using vectorizedIEEE.
+func archUpdateIEEE(crc uint32, p []byte) uint32 {
+	if !hasVX {
+		panic("not available")
+	}
+	// Use vectorized function if data length is above threshold.
+	if len(p) >= vxMinLen {
 		aligned := len(p) & ^vxAlignMask
 		crc = vectorizedIEEE(crc, p[:aligned])
 		p = p[aligned:]
-		// process remaining data
-		if len(p) > 0 {
-			crc = genericIEEE(crc, p)
-		}
+	}
+	if len(p) == 0 {
 		return crc
 	}
-	return genericIEEE(crc, p)
+	return slicingUpdate(crc, archIeeeTable8, p)
 }

src/hash/crc32/crc32_test.go

@@ -6,7 +6,7 @@ package crc32
 
 import (
 	"hash"
-	"io"
+	"math/rand"
 	"testing"
 )
 
@@ -49,42 +49,150 @@ var golden = []test{
 	{0x8e0bb443, 0xdcded527, "How can you write a big system without C++?  -Paul Glick"},
 }
 
+// testGoldenIEEE verifies that the given function returns
+// correct IEEE checksums.
+func testGoldenIEEE(t *testing.T, crcFunc func(b []byte) uint32) {
+	for _, g := range golden {
+		if crc := crcFunc([]byte(g.in)); crc != g.ieee {
+			t.Errorf("IEEE(%s) = 0x%x want 0x%x", g.in, crc, g.ieee)
+		}
+	}
+}
+
+// testGoldenCastagnoli verifies that the given function returns
+// correct IEEE checksums.
+func testGoldenCastagnoli(t *testing.T, crcFunc func(b []byte) uint32) {
+	for _, g := range golden {
+		if crc := crcFunc([]byte(g.in)); crc != g.castagnoli {
+			t.Errorf("Castagnoli(%s) = 0x%x want 0x%x", g.in, crc, g.castagnoli)
+		}
+	}
+}
+
+// testCrossCheck generates random buffers of various lengths and verifies that
+// the two "update" functions return the same result.
+func testCrossCheck(t *testing.T, crcFunc1, crcFunc2 func(crc uint32, b []byte) uint32) {
+	// The AMD64 implementation has some cutoffs at lengths 168*3=504 and
+	// 1344*3=4032. We should make sure lengths around these values are in the
+	// list.
+	lengths := []int{0, 1, 2, 3, 4, 5, 10, 16, 50, 100, 128,
+		500, 501, 502, 503, 504, 505, 512, 1000, 1024, 2000,
+		4030, 4031, 4032, 4033, 4036, 4040, 4048, 4096, 5000, 10000}
+	for _, length := range lengths {
+		p := make([]byte, length)
+		_, _ = rand.Read(p)
+		crcInit := uint32(rand.Int63())
+		crc1 := crcFunc1(crcInit, p)
+		crc2 := crcFunc2(crcInit, p)
+		if crc1 != crc2 {
+			t.Errorf("mismatch: 0x%x vs 0x%x (buffer length %d)", crc1, crc2, length)
+		}
+	}
+}
+
+// TestSimple tests the simple generic algorithm.
+func TestSimple(t *testing.T) {
+	tab := simpleMakeTable(IEEE)
+	testGoldenIEEE(t, func(b []byte) uint32 {
+		return simpleUpdate(0, tab, b)
+	})
+
+	tab = simpleMakeTable(Castagnoli)
+	testGoldenCastagnoli(t, func(b []byte) uint32 {
+		return simpleUpdate(0, tab, b)
+	})
+}
+
+// TestSimple tests the slicing-by-8 algorithm.
+func TestSlicing(t *testing.T) {
+	tab := slicingMakeTable(IEEE)
+	testGoldenIEEE(t, func(b []byte) uint32 {
+		return slicingUpdate(0, tab, b)
+	})
+
+	tab = slicingMakeTable(Castagnoli)
+	testGoldenCastagnoli(t, func(b []byte) uint32 {
+		return slicingUpdate(0, tab, b)
+	})
+
+	// Cross-check various polys against the simple algorithm.
+	for _, poly := range []uint32{IEEE, Castagnoli, Koopman, 0xD5828281} {
+		t1 := simpleMakeTable(poly)
+		f1 := func(crc uint32, b []byte) uint32 {
+			return simpleUpdate(crc, t1, b)
+		}
+		t2 := slicingMakeTable(poly)
+		f2 := func(crc uint32, b []byte) uint32 {
+			return slicingUpdate(crc, t2, b)
+		}
+		testCrossCheck(t, f1, f2)
+	}
+}
+
+func TestArchIEEE(t *testing.T) {
+	if !archAvailableIEEE() {
+		t.Skip("Arch-specific IEEE not available.")
+	}
+	archInitIEEE()
+	slicingTable := slicingMakeTable(IEEE)
+	testCrossCheck(t, archUpdateIEEE, func(crc uint32, b []byte) uint32 {
+		return slicingUpdate(crc, slicingTable, b)
+	})
+}
+
+func TestArchCastagnoli(t *testing.T) {
+	if !archAvailableCastagnoli() {
+		t.Skip("Arch-specific Castagnoli not available.")
+	}
+	archInitCastagnoli()
+	slicingTable := slicingMakeTable(Castagnoli)
+	testCrossCheck(t, archUpdateCastagnoli, func(crc uint32, b []byte) uint32 {
+		return slicingUpdate(crc, slicingTable, b)
+	})
+}
+
 func TestGolden(t *testing.T) {
+	testGoldenIEEE(t, ChecksumIEEE)
+
+	// Some implementations have special code to deal with misaligned
+	// data; test that as well.
+	for delta := 1; delta <= 7; delta++ {
+		testGoldenIEEE(t, func(b []byte) uint32 {
+			ieee := NewIEEE()
+			d := delta
+			if d >= len(b) {
+				d = len(b)
+			}
+			ieee.Write(b[:d])
+			ieee.Write(b[d:])
+			return ieee.Sum32()
+		})
+	}
+
 	castagnoliTab := MakeTable(Castagnoli)
 	if castagnoliTab == nil {
 		t.Errorf("nil Castagnoli Table")
 	}
 
-	for _, g := range golden {
-		ieee := NewIEEE()
-		io.WriteString(ieee, g.in)
-		s := ieee.Sum32()
-		if s != g.ieee {
-			t.Errorf("IEEE(%s) = 0x%x want 0x%x", g.in, s, g.ieee)
-		}
-
+	testGoldenCastagnoli(t, func(b []byte) uint32 {
 		castagnoli := New(castagnoliTab)
-		io.WriteString(castagnoli, g.in)
-		s = castagnoli.Sum32()
-		if s != g.castagnoli {
-			t.Errorf("Castagnoli(%s) = 0x%x want 0x%x", g.in, s, g.castagnoli)
-		}
+		castagnoli.Write(b)
+		return castagnoli.Sum32()
+	})
 
-		// The SSE4.2 implementation of this has code to deal
-		// with misaligned data so we ensure that we test that
-		// too.
-		for delta := 1; delta <= 7; delta++ {
-			if len(g.in) > delta {
-				in := []byte(g.in)
-				castagnoli = New(castagnoliTab)
-				castagnoli.Write(in[:delta])
-				castagnoli.Write(in[delta:])
-				s = castagnoli.Sum32()
-				if s != g.castagnoli {
-					t.Errorf("Castagnoli[misaligned](%s) = 0x%x want 0x%x", g.in, s, g.castagnoli)
-				}
+	// Some implementations have special code to deal with misaligned
+	// data; test that as well.
+	for delta := 1; delta <= 7; delta++ {
+		testGoldenCastagnoli(t, func(b []byte) uint32 {
+			castagnoli := New(castagnoliTab)
+			d := delta
+			if d >= len(b) {
+				d = len(b)
 			}
-		}
+			castagnoli.Write(b[:d])
+			castagnoli.Write(b[d:])
+			return castagnoli.Sum32()
+		})
 	}
 }