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    crc-32

Pure-JS CRC-32


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Package description

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

Readme

Source

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:

// var CRC32 = require('crc-32');             // uncomment this line if in node
CRC32.str("SheetJS")                          // -1647298270
CRC32.bstr("SheetJS")                         // -1647298270
CRC32.buf([ 83, 104, 101, 101, 116, 74, 83 ]) // -1647298270

crc32 = CRC32.buf([83, 104])                  // -1826163454  "Sh"
crc32 = CRC32.str("eet", crc32)               //  1191034598  "Sheet"
CRC32.bstr("JS", crc32)                       // -1647298270  "SheetJS"

[CRC32.str("\u2603"),  CRC32.str("\u0003")]   // [ -1743909036,  1259060791 ]
[CRC32.bstr("\u2603"), CRC32.bstr("\u0003")]  // [  1259060791,  1259060791 ]
[CRC32.buf([0x2603]),  CRC32.buf([0x0003])]   // [  1259060791,  1259060791 ]

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

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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Last updated on 12 Oct 2016

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