Skip to content

Instantly share code, notes, and snippets.

@sebastien-p
Created June 14, 2011 09:10
Show Gist options
  • Star 4 You must be signed in to star a gist
  • Fork 2 You must be signed in to fork a gist
  • Save sebastien-p/1024553 to your computer and use it in GitHub Desktop.
Save sebastien-p/1024553 to your computer and use it in GitHub Desktop.
Tweet-sized JavaScript implementation of the Lempel–Ziv–Welch universal lossless data compression algorithm.
// Please, see http://rosettacode.org/wiki/LZW_compression#JavaScript
// and http://en.wikipedia.org/wiki/Lempel–Ziv–Welch for more infos.
function (
a // String to compress and placeholder for 'wc'.
){
for (
var b = a + "Ā", // Append first "illegal" character (charCode === 256).
c = [], // dictionary
d = 0, // dictionary size
e = d, // iterator
f = c, // w
g = c, // result
h; // c
h = b.charAt(e++);
)
c[h] = h.charCodeAt(), // Fill in the dictionary ...
f = 1 + c[a = f + h] ? a : (g[d++] = c[f], c[a] = d + 255, h); // ... and use it to compress data.
return g // Array of compressed data.
}
function(a){for(var b=a+"Ā",c=[],d=0,e=d,f=c,g=c,h;h=b.charAt(e++);)c[h]=h.charCodeAt(),f=1+c[a=f+h]?a:(g[d++]=c[f],c[a]=d+255,h);return g}
DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
Version 2, December 2004
Copyright (C) 2011 Sebastien P. https://twitter.com/#!/_sebastienp
Special thanks to @subzey (you rock) and @kbjr !
Everyone is permitted to copy and distribute verbatim or modified
copies of this license document, and changing it is allowed as long
as the name is changed.
DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
0. You just DO WHAT THE FUCK YOU WANT TO.
{
"name": "LZWcompress",
"description": "JavaScript implementation of the Lempel–Ziv–Welch universal lossless data compression algorithm.",
"keywords": [
"LZW",
"lossless",
"data",
"compression"
]
}
<!DOCTYPE html>
<title>Foo</title>
<div>Expected value: <b>84,79,66,69,79,82,78,79,84,256,258,260,265,259,261,263</b></div>
<div>Actual value: <b id="ret"></b></div>
<script>
var LZWcompress = function(a){for(var b=a+"Ā",c=[],d=0,e=d,f=c,g=c,h;h=b.charAt(e++);)c[h]=h.charCodeAt(),f=1+c[a=f+h]?a:(g[d++]=c[f],c[a]=d+255,h);return g}
document.getElementById("ret").innerHTML = LZWcompress("TOBEORNOTTOBEORTOBEORNOT")
</script>
@bytespider
Copy link

Well done guys, this truly is awesome

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment