bin | ||
bits | ||
ctest | ||
demo | ||
misc | ||
perf | ||
test_files | ||
types | ||
.eslintrc | ||
.flowconfig | ||
.gitignore | ||
.jscs.json | ||
.jshintrc | ||
.npmignore | ||
.spelling | ||
.travis.yml | ||
adler32.flow.js | ||
adler32.js | ||
index.html | ||
large.html | ||
LICENSE | ||
Makefile | ||
package.json | ||
README.md | ||
shim.js | ||
test.js |
adler32
Signed ADLER-32 algorithm implementation in JS (for the browser and nodejs). Emphasis on correctness, performance, and IE6+ support.
Installation
With npm:
$ npm install adler-32
In the browser:
<script src="adler32.js"></script>
The browser exposes a variable ADLER32
.
When installed globally, npm installs a script adler32
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_ADLER
.
Usage
In all cases, the relevant function takes an argument representing data and an optional second argument representing the starting "seed" (for running hash).
The return value is a signed 32-bit integer.
-
ADLER32.buf(byte array or buffer[, seed])
assumes the argument is a sequence of 8-bit unsigned integers (nodejsBuffer
,Uint8Array
or array of bytes). -
ADLER32.bstr(binary string[, seed])
assumes the argument is a binary string where bytei
is the low byte of the UCS-2 char:str.charCodeAt(i) & 0xFF
-
ADLER32.str(string)
assumes the argument is a standard JS string and calculates the hash of the UTF-8 encoding.
For example:
// var ADLER32 = require('adler-32'); // uncomment if in node
ADLER32.str("SheetJS") // 176947863
ADLER32.bstr("SheetJS") // 176947863
ADLER32.buf([ 83, 104, 101, 101, 116, 74, 83 ]) // 176947863
adler32 = ADLER32.buf([83, 104]) // 17825980 "Sh"
adler32 = ADLER32.str("eet", adler32) // 95486458 "Sheet"
ADLER32.bstr("JS", adler32) // 176947863 "SheetJS"
[ADLER32.str("\u2603"), ADLER32.str("\u0003")] // [ 73138686, 262148 ]
[ADLER32.bstr("\u2603"), ADLER32.bstr("\u0003")] // [ 262148, 262148 ]
[ADLER32.buf([0x2603]), ADLER32.buf([0x0003])] // [ 262148, 262148 ]
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 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
The included adler32.njs
script can process files or standard input:
$ echo "this is a test" > t.txt
$ bin/adler32.njs t.txt
726861088
For comparison, the included adler32.py
script uses python zlib
:
$ bin/adler32.py t.txt
726861088
Performance
make perf
will run algorithmic performance tests (which should justify certain
decisions in the code).
Bit twiddling is much faster than taking the mod in Safari and Firefox browsers.
Instead of taking the literal mod 65521, it is faster to keep it in the integers
by bit-shifting: 65536 ~ 15 mod 65521
so for nonnegative integer a
:
a = (a >>> 16) * 65536 + (a & 65535) [equality]
a ~ (a >>> 16) * 15 + (a & 65535) mod 65521
The mod is taken at the very end, since the intermediate result may exceed 65521
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.