What is crc-32?
The crc-32 npm package is a JavaScript library for calculating CRC32 checksums. CRC32 is a checksum algorithm that generates a 32-bit hash of data, which can be used to verify the integrity of data during transmission or storage. This package provides functions to compute CRC32 checksums for strings and byte arrays.
What are crc-32's main functionalities?
CRC32 checksum from a string
This feature allows you to compute the CRC32 checksum of a given string. The 'crc32.str' function takes a string as input and returns the checksum as a signed 32-bit integer.
"use strict";
var crc32 = require('crc-32');
var str = 'Hello World';
var checksum = crc32.str(str);
console.log('Checksum for string:', checksum);
CRC32 checksum from a byte array
This feature allows you to compute the CRC32 checksum of a byte array. The 'crc32.buf' function takes a byte array (Uint8Array) as input and returns the checksum as a signed 32-bit integer.
"use strict";
var crc32 = require('crc-32');
var buf = new Uint8Array([72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100]);
var checksum = crc32.buf(buf);
console.log('Checksum for byte array:', checksum);
Other packages similar to crc-32
crc
The 'crc' npm package is similar to 'crc-32' and provides CRC checksum calculation for multiple CRC algorithms, including CRC32. It offers a wider range of CRC algorithms compared to 'crc-32', which is focused solely on CRC32.
buffer-crc32
The 'buffer-crc32' npm package is another alternative that provides CRC32 checksum calculation. It is designed to work with Node.js buffers and can be used to append the checksum to the buffer. It is similar to 'crc-32' but with a focus on Node.js buffer compatibility.
crc32
Standard CRC-32 algorithm implementation in JS (for the browser and nodejs).
Emphasis on correctness, performance, and IE6+ support.
Installation
With npm:
$ npm install crc-32
In the browser:
<script src="crc32.js"></script>
The browser exposes a variable CRC32
.
When installed globally, npm installs a script crc32
that computes the
checksum for a specified file or standard input.
The script will manipulate module.exports
if available (e.g. in a CommonJS
require
context). This is not always desirable. To prevent the behavior,
define DO_NOT_EXPORT_CRC
.
Usage
In all cases, the relevant function takes an argument representing data and an
optional second argument representing the starting "seed" (for rolling CRC).
The return value is a signed 32-bit integer.
-
CRC32.buf(byte array or buffer[, seed])
assumes the argument is a sequence
of 8-bit unsigned integers (e.g. nodejs Buffer
or simple array of ints).
-
CRC32.bstr(binary string[, seed])
assumes the argument is a "binary" string
where byte i
is the low byte of the UCS-2 char: str.charCodeAt(i) & 0xFF
-
CRC32.str(string[, seed])
assumes the argument is a standard string and
calculates the CRC32 of the UTF-8 encoding.
For example:
CRC32.str("SheetJS")
CRC32.bstr("SheetJS")
CRC32.buf([ 83, 104, 101, 101, 116, 74, 83 ])
crc32 = CRC32.buf([83, 104])
crc32 = CRC32.str("eet", crc32)
CRC32.bstr("JS", crc32)
[CRC32.str("\u2603"), CRC32.str("\u0003")]
[CRC32.bstr("\u2603"), CRC32.bstr("\u0003")]
[CRC32.buf([0x2603]), CRC32.buf([0x0003])]
Testing
make test
will run the nodejs-based test.
To run the in-browser tests, run a local server and go to the ctest
directory.
make ctestserv
will start a python SimpleHTTPServer
server on port 8000.
To update the browser artifacts, run make ctest
.
To generate the bits file, use the crc32
function from python zlib:
>>> from zlib import crc32
>>> x="foo bar baz٪☃🍣"
>>> crc32(x)
1531648243
>>> crc32(x+x)
-218791105
>>> crc32(x+x+x)
1834240887
The included crc32.njs
script can process files or stdin:
$ echo "this is a test" > t.txt
$ bin/crc32.njs t.txt
1912935186
For comparison, the included crc32.py
script uses python zlib:
$ bin/crc32.py t.txt
1912935186
On OSX the command cksum
generates unsigned CRC-32 with Algorithm 3:
$ cksum -o 3 < IE8.Win7.For.Windows.VMware.zip
1891069052 4161613172
$ crc32 --unsigned ~/Downloads/IE8.Win7.For.Windows.VMware.zip
1891069052
Performance
make perf
will run algorithmic performance tests (which should justify certain
decisions in the code).
js-adler32 has more performance notes
License
Please consult the attached LICENSE file for details. All rights not explicitly
granted by the Apache 2.0 license are reserved by the Original Author.
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