js-crc32/README.md

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# crc32
Standard CRC-32 algorithm implementation in JS (for the browser and nodejs).
Emphasis on correctness, performance, and IE6+ support.
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## Installation
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With [npm](https://www.npmjs.org/package/crc-32):
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```bash
$ npm install crc-32
```
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In the browser:
```html
<script src="crc32.js"></script>
```
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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.
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The script will manipulate `module.exports` if available . This is not always
desirable. To prevent the behavior, define `DO_NOT_EXPORT_CRC`.
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## Usage
In all cases, the relevant function takes an argument representing data and an
optional second argument representing the starting "seed" (for rolling CRC).
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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 (nodejs `Buffer`, `Uint8Array` or array of bytes).
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- `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`
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- `CRC32.str(string[, seed])` assumes the argument is a standard JS string and
calculates the hash of the UTF-8 encoding.
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For example:
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```js
// 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 ]
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```
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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.
`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`:
```python
>>> from zlib import crc32
>>> x="foo bar baz٪☃🍣"
>>> crc32(x)
1531648243
>>> crc32(x+x)
-218791105
>>> crc32(x+x+x)
1834240887
```
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The included `crc32.njs` script can process files or standard input:
```bash
$ echo "this is a test" > t.txt
$ bin/crc32.njs t.txt
1912935186
```
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For comparison, the included `crc32.py` script uses python `zlib`:
```bash
$ bin/crc32.py t.txt
1912935186
```
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On OSX the command `cksum` generates unsigned CRC-32 with Algorithm 3:
```bash
$ 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).
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The [`adler-32` project](http://git.io/adler32) has more performance notes
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## 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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## Badges
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[![Sauce Test Status](https://saucelabs.com/browser-matrix/crc32.svg)](https://saucelabs.com/u/crc32)
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[![Build Status](https://travis-ci.org/SheetJS/js-crc32.svg?branch=master)](https://travis-ci.org/SheetJS/js-crc32)
[![Coverage Status](http://img.shields.io/coveralls/SheetJS/js-crc32/master.svg)](https://coveralls.io/r/SheetJS/js-crc32?branch=master)
[![Dependencies Status](https://david-dm.org/sheetjs/js-crc32/status.svg)](https://david-dm.org/sheetjs/js-crc32)
[![NPM Downloads](https://img.shields.io/npm/dt/crc-32.svg)](https://npmjs.org/package/crc-32)
[![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)