Skip to content

Instantly share code, notes, and snippets.

@sebastien-p
Forked from 140bytes/LICENSE.txt
Created June 15, 2011 15:49
Show Gist options
  • Star 9 You must be signed in to star a gist
  • Fork 3 You must be signed in to fork a gist
  • Save sebastien-p/1027389 to your computer and use it in GitHub Desktop.
Save sebastien-p/1027389 to your computer and use it in GitHub Desktop.
LZW compression
// 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>
@sebastien-p
Copy link
Author

See original gist comments here : https://gist.github.com/1024553#comments

@mathiasbynens
Copy link

Nice work!

Heads up: I get an Uncaught SyntaxError: Unexpected identifier in test.html.

@sebastien-p
Copy link
Author

@mathiasbynens : how exactly can I reproduce the problem ? OS ? browser ? ...

@mathiasbynens
Copy link

My bad. I was checking using…

data:text/html;charset=utf-8,<!DOCTYPE%20html><title>Foo</title><div>Expected%20value%3A%20<b>84,79,66,69,79,82,78,79,84,256,258,260,265,259,261,263</b></div><div>Actual%20value%3A%20<b%20id="ret"></b></div><script>var%20LZWcompress%20=%20function(a){for(var%20b=a+"%C4%80",c=%5B%5D,d=0,e=d,f=c,g=c,h;h=b.charAt(e++);)c%5Bh%5D=h.charCodeAt(),f=1+c%5Ba=f+h%5D%3Fa%3A(g%5Bd++%5D=c%5Bf%5D,c%5Ba%5D=d+255,h);return%20g}document.getElementById("ret").innerHTML%20=%20LZWcompress("TOBEORNOTTOBEORTOBEORNOT")</script>

(New lines got cut out while pasting in my location bar – and because of the missing semicolons the whole thing broke.)

@atk
Copy link

atk commented Jun 16, 2011

Hey, @sebastien-p

Great that you've started this! Thank you!
If you don't care for compatibility with IE7 or older, you can omit .charAt and use b[e++], thus saving 7 bytes.

@jed: could it be official canon that IE-compatibility may start with version 8?

Greetings, atk

@sebastien-p
Copy link
Author

@atk : thanks. I know about b[e++] but why not offering IE<8 compatibility if we can ?

@atk
Copy link

atk commented Jun 16, 2011

Like we used to say: One byte saved is one byte earned... maybe we can get enough space for String.fromCharCode.

@sebastien-p
Copy link
Author

@atk : I don't understand, there's no need of String.fromCharCode anymore, where do you want it to be ?

@atk
Copy link

atk commented Jun 16, 2011

@sebastien-p : Depends on what you expect as output.

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