js-adler32/README.md

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2014-06-18 17:58:20 +00:00
# adler32
Signed ADLER-32 algorithm implementation in JS (for the browser and nodejs).
Emphasis on correctness and performance.
## Installation
In [nodejs](https://www.npmjs.org/package/adler-32):
npm install adler-32
In the browser:
<script lang="javascript" src="adler32.js"></script>
The browser exposes a variable ADLER32
## Usage
- `ADLER32.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)
- `ADLER32.bstr(binary string)` interprets the argument as a binary string where
the `i`-th byte is `str.charCodeAt(i)`
- `ADLER32.str(string)` interprets the argument as a standard JS string
## 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. To update the browser artifacts,
run `make ctest`.
To generate the bits file, use the `adler32` function from python zlib:
```
>>> from zlib import adler32
>>> x="foo bar baz٪☃🍣"
>>> adler32(x)
1543572022
>>> adler32(x+x)
-2076896149
>>> adler32(x+x+x)
2023497376
```
## Performance
`make perf` will run algorithmic performance tests (which should justify certain
decisions in the code).
[js-crc](http://git.io/crc32) has more performance notes
## Magic Number
The magic numbers were chosen so as to not overflow a 31-bit integer:
```
F[n_] := Reduce[x*(x + 1)*n/2 + (x + 1)*(65521) < (2^31 - 1) && x > 0, x, Integers]
F[255] (* bstr: x \[Element] Integers && 1 <= x <= 3854 *)
F[127] (* ascii: x \[Element] Integers && 1 <= x <= 5321 *)
```
Subtract up to 4 elements for the unicode case.
## 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.
[![Build Status](https://travis-ci.org/SheetJS/js-adler32.svg?branch=master)](https://travis-ci.org/SheetJS/js-adler32)
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