Package Exports

crc-32

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (crc-32) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

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

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.

crc-32