crc32

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

Installation

With npm:

$ npm install crc-32

In the browser:

<script src="crc32.js"></script>

The browser exposes a variable ADLER32

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 a single argument representing data.

The return value is a signed 32-bit integer.

• CRC32.buf(byte array or buffer) assumes the argument is a set of 8-bit unsigned integers (e.g. nodejs Buffer or simple array of ints).

• CRC32.bstr(binary string) interprets the argument as a binary string where the i-th byte is the low byte of the UCS-2 char: str.charCodeAt(i) & 0xFF

• CRC32.str(string) interprets the argument as a standard JS string

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.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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