1 files changed, 265 insertions, 0 deletions
diff --git a/src/hash/crc32/crc32.go b/src/hash/crc32/crc32.go
new file mode 100644
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+++ b/src/hash/crc32/crc32.go
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+// 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 implements the 32-bit cyclic redundancy check, or CRC-32,
+// checksum. See https://en.wikipedia.org/wiki/Cyclic_redundancy_check for
+// information.
+//
+// Polynomials are represented in LSB-first form also known as reversed representation.
+//
+// See https://en.wikipedia.org/wiki/Mathematics_of_cyclic_redundancy_checks#Reversed_representations_and_reciprocal_polynomials
+// for information.
+package crc32
+
+import (
+	"errors"
+	"hash"
+	"sync"
+	"sync/atomic"
+)
+
+// The size of a CRC-32 checksum in bytes.
+const Size = 4
+
+// Predefined polynomials.
+const (
+	// IEEE is by far and away the most common CRC-32 polynomial.
+	// Used by ethernet (IEEE 802.3), v.42, fddi, gzip, zip, png, ...
+	IEEE = 0xedb88320
+
+	// Castagnoli's polynomial, used in iSCSI.
+	// Has better error detection characteristics than IEEE.
+	// https://dx.doi.org/10.1109/26.231911
+	Castagnoli = 0x82f63b78
+
+	// Koopman's polynomial.
+	// Also has better error detection characteristics than IEEE.
+	// https://dx.doi.org/10.1109/DSN.2002.1028931
+	Koopman = 0xeb31d82e
+)
+
+// 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 updateCastagnoli func(crc uint32, p []byte) uint32
+var castagnoliOnce sync.Once
+var haveCastagnoli atomic.Bool
+
+func castagnoliInit() {
+	castagnoliTable = simpleMakeTable(Castagnoli)
+
+	if archAvailableCastagnoli() {
+		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)
+		}
+	}
+
+	haveCastagnoli.Store(true)
+}
+
+// IEEETable is the table for the IEEE polynomial.
+var IEEETable = simpleMakeTable(IEEE)
+
+// ieeeTable8 is the slicing8Table for IEEE
+var ieeeTable8 *slicing8Table
+var updateIEEE func(crc uint32, p []byte) uint32
+var ieeeOnce sync.Once
+
+func ieeeInit() {
+	if archAvailableIEEE() {
+		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
+	default:
+		return simpleMakeTable(poly)
+	}
+}
+
+// digest represents the partial evaluation of a checksum.
+type digest struct {
+	crc uint32
+	tab *Table
+}
+
+// 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. The returned Hash32 also
+// implements encoding.BinaryMarshaler and encoding.BinaryUnmarshaler to
+// marshal and unmarshal the internal state of the hash.
+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. Its Sum method will lay the value out in
+// big-endian byte order. The returned Hash32 also implements
+// encoding.BinaryMarshaler and encoding.BinaryUnmarshaler to marshal
+// and unmarshal the internal state of the hash.
+func NewIEEE() hash.Hash32 { return New(IEEETable) }
+
+func (d *digest) Size() int { return Size }
+
+func (d *digest) BlockSize() int { return 1 }
+
+func (d *digest) Reset() { d.crc = 0 }
+
+const (
+	magic         = "crc\x01"
+	marshaledSize = len(magic) + 4 + 4
+)
+
+func (d *digest) MarshalBinary() ([]byte, error) {
+	b := make([]byte, 0, marshaledSize)
+	b = append(b, magic...)
+	b = appendUint32(b, tableSum(d.tab))
+	b = appendUint32(b, d.crc)
+	return b, nil
+}
+
+func (d *digest) UnmarshalBinary(b []byte) error {
+	if len(b) < len(magic) || string(b[:len(magic)]) != magic {
+		return errors.New("hash/crc32: invalid hash state identifier")
+	}
+	if len(b) != marshaledSize {
+		return errors.New("hash/crc32: invalid hash state size")
+	}
+	if tableSum(d.tab) != readUint32(b[4:]) {
+		return errors.New("hash/crc32: tables do not match")
+	}
+	d.crc = readUint32(b[8:])
+	return nil
+}
+
+func appendUint32(b []byte, x uint32) []byte {
+	a := [4]byte{
+		byte(x >> 24),
+		byte(x >> 16),
+		byte(x >> 8),
+		byte(x),
+	}
+	return append(b, a[:]...)
+}
+
+func readUint32(b []byte) uint32 {
+	_ = b[3]
+	return uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
+}
+
+func update(crc uint32, tab *Table, p []byte, checkInitIEEE bool) uint32 {
+	switch {
+	case haveCastagnoli.Load() && tab == castagnoliTable:
+		return updateCastagnoli(crc, p)
+	case tab == IEEETable:
+		if checkInitIEEE {
+			ieeeOnce.Do(ieeeInit)
+		}
+		return updateIEEE(crc, p)
+	default:
+		return simpleUpdate(crc, tab, p)
+	}
+}
+
+// Update returns the result of adding the bytes in p to the crc.
+func Update(crc uint32, tab *Table, p []byte) uint32 {
+	// 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.
+	return update(crc, tab, p, true)
+}
+
+func (d *digest) Write(p []byte) (n int, err error) {
+	// We only create digest objects through New() which takes care of
+	// initialization in this case.
+	d.crc = update(d.crc, d.tab, p, false)
+	return len(p), nil
+}
+
+func (d *digest) Sum32() uint32 { return d.crc }
+
+func (d *digest) Sum(in []byte) []byte {
+	s := d.Sum32()
+	return append(in, byte(s>>24), byte(s>>16), byte(s>>8), byte(s))
+}
+
+// Checksum returns the CRC-32 checksum of data
+// using the polynomial represented by the Table.
+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 {
+	ieeeOnce.Do(ieeeInit)
+	return updateIEEE(0, data)
+}
+
+// tableSum returns the IEEE checksum of table t.
+func tableSum(t *Table) uint32 {
+	var a [1024]byte
+	b := a[:0]
+	if t != nil {
+		for _, x := range t {
+			b = appendUint32(b, x)
+		}
+	}
+	return ChecksumIEEE(b)
+}