decodeBase64.js

/**
 * This code snippet came from an answer I posted on stackoverflow and was derived from work presented
 * among other answers and comments. The post is here:
 *   http://stackoverflow.com/questions/2820249/base64-encoding-and-decoding-in-client-side-javascript/15016605#15016605
 * 
 * This is not very readable code, and would be better served by being written out such that it is understandable, and
 * letting a minifier tool do the minification. However, it does work and is easy to copy and paste where needed rather
 * than creating a larger library dependency when that is not desirable. So take it at face value.
 * 
 * I posted it here when someone requested to use it and asked about a license. You are free to use this code however
 * you wish -- copy it, modify it, distribute it. I make no claims on it, and I do not ask for attribution. I also do not
 * warrant anything, so use this code at your own risk.
 * 
 */

/**
 * This function presumes a well formed base64 string 's' with no carriage returns.
 */
decodeBase64 = function(s) {
    var e={},i,b=0,c,x,l=0,a,r='',w=String.fromCharCode,L=s.length;
    var A="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    for(i=0;i<64;i++){e[A.charAt(i)]=i;}
    for(x=0;x<L;x++){
        c=e[s.charAt(x)];b=(b<<6)+c;l+=6;
        while(l>=8){((a=(b>>>(l-=8))&0xff)||(x<(L-2)))&&(r+=w(a));}
    }
    return r;
};