Standard CRC-32 algorithm implementation in JS (for the browser and nodejs). Emphasis on correctness, performance, and IE6+ support.

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 . This is not always desirable. To prevent the behavior, define DO_NOT_EXPORT_CRC.

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 (nodejs Buffer, Uint8Array or array of bytes).

• 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 JS string and calculates the hash 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 ]

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 standard input:

$ 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

make perf will run algorithmic performance tests (which should justify certain decisions in the code).

The adler-32 project has more performance notes

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.