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sebastien-p/LICENSE.txt

Created June 14, 2011 09:10
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Tweet-sized JavaScript implementation of the Lempel–Ziv–Welch universal lossless data compression algorithm.
Raw
annotated.js
// 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.
}
Raw
index.js
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}
Raw
LICENSE.txt
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.
Raw
package.json
{
"name": "LZWcompress",
"description": "JavaScript implementation of the Lempel–Ziv–Welch universal lossless data compression algorithm.",
"keywords": [
"LZW",
"lossless",
"data",
"compression"
]
}
Raw
test.html
<!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
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@subzey : you rock !

The only thing left is to make enough room to write g = a.charAt(d++); instead of g = a[d++]; !

@subzey
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subzey commented Jun 15, 2011

function(h){for(var a=h+'ħ',b=[],c=0,d=b,e=b,f=b,g;g=a.charAt(d++);)b[g]=g.charCodeAt(),e=1+b[h=e+g]?h:(f[c++]=b[e],b[h]=c+255,g);return f}
139 chars, 140 bytes, works perfectly well in IE6, IE8, IE9 (didn't test in native IE7)

Optimizations applied:

  • c is initially 0, not 256, used post-decrement instead of pre-decrement
  • push changed to index-based assignment as if c starts with 0, index is always equal to c
  • Rearranged variables declaration and «illegal» char appending, stripping one byte

@sebastien-p
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@subzey : Wonderful ! IE7 should not be a problem. I did something like that to say goodbye to push but gave up on it in the end.

@bytespider
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Well done guys, this truly is awesome

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