From 754bbf7a25a8dda49b5d08ef0d0443bbf5af0e36 Mon Sep 17 00:00:00 2001 From: Craig Jennings Date: Sun, 7 Apr 2024 13:41:34 -0500 Subject: new repository --- devdocs/go/hash%2Fcrc32%2Findex.html | 62 ++++++++++++++++++++++++++++++++++++ 1 file changed, 62 insertions(+) create mode 100644 devdocs/go/hash%2Fcrc32%2Findex.html (limited to 'devdocs/go/hash%2Fcrc32%2Findex.html') diff --git a/devdocs/go/hash%2Fcrc32%2Findex.html b/devdocs/go/hash%2Fcrc32%2Findex.html new file mode 100644 index 00000000..65aed132 --- /dev/null +++ b/devdocs/go/hash%2Fcrc32%2Findex.html @@ -0,0 +1,62 @@ +

Package crc32

Overview

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.

Index

Examples

MakeTable

Package files

crc32.go crc32_amd64.go crc32_generic.go

Constants

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
+)

The size of a CRC-32 checksum in bytes.

+
const Size = 4

Variables

IEEETable is the table for the IEEE polynomial.

+
var IEEETable = simpleMakeTable(IEEE)

func Checksum 

func Checksum(data []byte, tab *Table) uint32

Checksum returns the CRC-32 checksum of data using the polynomial represented by the Table.

+

func ChecksumIEEE 

func ChecksumIEEE(data []byte) uint32

ChecksumIEEE returns the CRC-32 checksum of data using the IEEE polynomial.

+

func New 

func New(tab *Table) hash.Hash32

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 NewIEEE 

func NewIEEE() hash.Hash32

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 Update 

func Update(crc uint32, tab *Table, p []byte) uint32

Update returns the result of adding the bytes in p to the crc.

+

type Table

Table is a 256-word table representing the polynomial for efficient processing.

+
type Table [256]uint32

func MakeTable 

func MakeTable(poly uint32) *Table

MakeTable returns a Table constructed from the specified polynomial. The contents of this Table must not be modified.

Example +

Code:

// In this package, the CRC polynomial is represented in reversed notation,
+// or LSB-first representation.
+//
+// LSB-first representation is a hexadecimal number with n bits, in which the
+// most significant bit represents the coefficient of x⁰ and the least significant
+// bit represents the coefficient of xⁿ⁻¹ (the coefficient for xⁿ is implicit).
+//
+// For example, CRC32-Q, as defined by the following polynomial,
+//	x³²+ x³¹+ x²⁴+ x²²+ x¹⁶+ x¹⁴+ x⁸+ x⁷+ x⁵+ x³+ x¹+ x⁰
+// has the reversed notation 0b11010101100000101000001010000001, so the value
+// that should be passed to MakeTable is 0xD5828281.
+crc32q := crc32.MakeTable(0xD5828281)
+fmt.Printf("%08x\n", crc32.Checksum([]byte("Hello world"), crc32q))
+

Output:

2964d064
+
+

+ © Google, Inc.
Licensed under the Creative Commons Attribution License 3.0.
+ http://golang.org/pkg/hash/crc32/ +

+
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