2014-06-16 21:27:47 +00:00
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# crc32
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Standard CRC-32 algorithm implementation in JS (for the browser and nodejs).
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2016-10-08 18:48:03 +00:00
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Emphasis on correctness, performance, and IE6+ support.
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2014-06-16 21:27:47 +00:00
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## Installation
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2015-05-06 21:47:18 +00:00
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With [npm](https://www.npmjs.org/package/crc-32):
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2014-06-16 21:27:47 +00:00
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2016-10-08 18:48:03 +00:00
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```bash
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$ npm install crc-32
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```
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2014-06-16 21:27:47 +00:00
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In the browser:
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```html
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<script src="crc32.js"></script>
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```
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2014-06-16 21:27:47 +00:00
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2016-10-08 18:48:03 +00:00
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The browser exposes a variable `CRC32`.
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When installed globally, npm installs a script `crc32` that computes the
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checksum for a specified file or standard input.
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2015-05-06 21:47:18 +00:00
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The script will manipulate `module.exports` if available (e.g. in a CommonJS
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`require` context). This is not always desirable. To prevent the behavior,
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define `DO_NOT_EXPORT_CRC`.
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## Usage
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2016-10-08 18:48:03 +00:00
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In all cases, the relevant function takes an argument representing data and an
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optional second argument representing the starting "seed" (for rolling CRC).
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2015-05-06 21:47:18 +00:00
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The return value is a signed 32-bit integer.
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- `CRC32.buf(byte array or buffer[, seed])` assumes the argument is a sequence
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of 8-bit unsigned integers (e.g. nodejs `Buffer` or simple array of ints).
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- `CRC32.bstr(binary string[, seed])` assumes the argument is a "binary" string
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where byte `i` is the low byte of the UCS-2 char: `str.charCodeAt(i) & 0xFF`
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- `CRC32.str(string[, seed])` assumes the argument is a standard string and
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calculates the CRC32 of the UTF-8 encoding.
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2014-06-17 23:20:41 +00:00
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2015-05-06 21:47:18 +00:00
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For example:
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2015-05-06 21:47:18 +00:00
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```js
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// var CRC32 = require('crc-32'); // uncomment this line if in node
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CRC32.str("SheetJS") // -1647298270
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CRC32.bstr("SheetJS") // -1647298270
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CRC32.buf([ 83, 104, 101, 101, 116, 74, 83 ]) // -1647298270
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crc32 = CRC32.buf([83, 104]) // -1826163454 "Sh"
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crc32 = CRC32.str("eet", crc32) // 1191034598 "Sheet"
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CRC32.bstr("JS", crc32) // -1647298270 "SheetJS"
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[CRC32.str("\u2603"), CRC32.str("\u0003")] // [ -1743909036, 1259060791 ]
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[CRC32.bstr("\u2603"), CRC32.bstr("\u0003")] // [ 1259060791, 1259060791 ]
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[CRC32.buf([0x2603]), CRC32.buf([0x0003])] // [ 1259060791, 1259060791 ]
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```
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2014-06-16 21:34:13 +00:00
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## Testing
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`make test` will run the nodejs-based test.
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To run the in-browser tests, run a local server and go to the `ctest` directory.
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`make ctestserv` will start a python `SimpleHTTPServer` server on port 8000.
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To update the browser artifacts, run `make ctest`.
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To generate the bits file, use the `crc32` function from python zlib:
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```python
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>>> from zlib import crc32
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>>> x="foo bar baz٪☃🍣"
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>>> crc32(x)
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1531648243
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>>> crc32(x+x)
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-218791105
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>>> crc32(x+x+x)
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1834240887
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```
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The included `crc32.njs` script can process files or stdin:
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```bash
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$ echo "this is a test" > t.txt
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$ bin/crc32.njs t.txt
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1912935186
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```
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For comparison, the included `crc32.py` script uses python zlib:
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```bash
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$ bin/crc32.py t.txt
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1912935186
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```
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2017-04-27 21:29:43 +00:00
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On OSX the command `cksum` generates unsigned CRC-32 with Algorithm 3:
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```bash
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$ cksum -o 3 < IE8.Win7.For.Windows.VMware.zip
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1891069052 4161613172
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$ crc32 --unsigned ~/Downloads/IE8.Win7.For.Windows.VMware.zip
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1891069052
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```
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## Performance
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`make perf` will run algorithmic performance tests (which should justify certain
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decisions in the code).
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[js-adler32](http://git.io/adler32) has more performance notes
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2016-01-13 03:30:35 +00:00
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2014-06-16 21:27:47 +00:00
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## License
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Please consult the attached LICENSE file for details. All rights not explicitly
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granted by the Apache 2.0 license are reserved by the Original Author.
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2015-05-06 21:47:18 +00:00
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## Badges
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2014-06-16 21:27:47 +00:00
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2016-10-10 23:45:29 +00:00
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[![Sauce Test Status](https://saucelabs.com/browser-matrix/crc32.svg)](https://saucelabs.com/u/crc32)
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2015-05-06 21:47:18 +00:00
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[![Build Status](https://travis-ci.org/SheetJS/js-crc32.svg?branch=master)](https://travis-ci.org/SheetJS/js-crc32)
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[![Coverage Status](http://img.shields.io/coveralls/SheetJS/js-crc32/master.svg)](https://coveralls.io/r/SheetJS/js-crc32?branch=master)
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2017-09-14 05:28:47 +00:00
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[![Dependencies Status](https://david-dm.org/sheetjs/js-crc32/status.svg)](https://david-dm.org/sheetjs/js-crc32)
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[![NPM Downloads](https://img.shields.io/npm/dt/crc-32.svg)](https://npmjs.org/package/crc-32)
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[![ghit.me](https://ghit.me/badge.svg?repo=sheetjs/js-xlsx)](https://ghit.me/repo/sheetjs/js-xlsx)
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[![Analytics](https://ga-beacon.appspot.com/UA-36810333-1/SheetJS/js-crc32?pixel)](https://github.com/SheetJS/js-crc32)
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