JarCastingcrc32
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 . 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 (nodejsBuffer,Uint8Arrayor array of bytes). -
CRC32.bstr(binary string[, seed])assumes the argument is a binary string where byteiis 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 ]
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 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
Performance
make perf will run algorithmic performance tests (which should justify certain decisions in the code).
The adler-32 project 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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