Encode/decode ASCII string to/from base64

base64.js

/**
 * Encode string into Base64, as defined by RFC 4648 [http://tools.ietf.org/html/rfc4648].
 * As per RFC 4648, no newlines are added.
 *
 * Characters in str must be within ISO-8859-1 with Unicode code point <= 256.
 *
 * Can be achieved JavaScript with btoa(), but this approach may be useful in other languages.
 *
 * @param {string} str ASCII/ISO-8859-1 string to be encoded as base-64.
 * @returns {string} Base64-encoded string.
 */
function Base64Encode(str) {
    if (/([^\u0000-\u00ff])/.test(str)) throw Error('String must be ASCII');

    var b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
    var o1, o2, o3, bits, h1, h2, h3, h4, e=[], pad = '', c;

    c = str.length % 3;  // pad string to length of multiple of 3
    if (c > 0) { while (c++ < 3) { pad += '='; str += '\0'; } }
    // note: doing padding here saves us doing special-case packing for trailing 1 or 2 chars

    for (c=0; c<str.length; c+=3) {  // pack three octets into four hexets
        o1 = str.charCodeAt(c);
        o2 = str.charCodeAt(c+1);
        o3 = str.charCodeAt(c+2);

        bits = o1<<16 | o2<<8 | o3;

        h1 = bits>>18 & 0x3f;
        h2 = bits>>12 & 0x3f;
        h3 = bits>>6 & 0x3f;
        h4 = bits & 0x3f;

        // use hextets to index into code string
        e[c/3] = b64.charAt(h1) + b64.charAt(h2) + b64.charAt(h3) + b64.charAt(h4);
    }
    str = e.join('');  // use Array.join() for better performance than repeated string appends

    // replace 'A's from padded nulls with '='s
    str = str.slice(0, str.length-pad.length) + pad;

    return str;
}

/**
 * Decode string from Base64, as defined by RFC 4648 [http://tools.ietf.org/html/rfc4648].
 * As per RFC 4648, newlines are not catered for.
 *
 * Can be achieved JavaScript with atob(), but this approach may be useful in other languages.
 *
 * @param {string} str Base64-encoded string.
 * @returns {string} Decoded ASCII/ISO-8859-1 string.
 */
function Base64Decode(str) {
    if (!(/^[a-z0-9+/]+={0,2}$/i.test(str)) || str.length%4 != 0) throw Error('Not base64 string');

    var b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
    var o1, o2, o3, h1, h2, h3, h4, bits, d=[];

    for (var c=0; c<str.length; c+=4) {  // unpack four hexets into three octets
        h1 = b64.indexOf(str.charAt(c));
        h2 = b64.indexOf(str.charAt(c+1));
        h3 = b64.indexOf(str.charAt(c+2));
        h4 = b64.indexOf(str.charAt(c+3));

        bits = h1<<18 | h2<<12 | h3<<6 | h4;

        o1 = bits>>>16 & 0xff;
        o2 = bits>>>8 & 0xff;
        o3 = bits & 0xff;

        d[c/4] = String.fromCharCode(o1, o2, o3);
        // check for padding
        if (h4 == 0x40) d[c/4] = String.fromCharCode(o1, o2);
        if (h3 == 0x40) d[c/4] = String.fromCharCode(o1);
    }
    str = d.join('');  // use Array.join() for better performance than repeated string appends

    return str;
}