Github's code for generating participation graphs

gistfile1.js

ParticipationGraph.prototype = {
    readData: function () {
        var a = this.data.split("\n");
        this.allCommits = a[0] ? this.base64BytesToIntArray(a[0]) : "";
        this.ownerCommits = a[1] ? this.base64BytesToIntArray(a[1]) : ""
    },
    // ...
    base64ByteToInt: function (a) {
        // This is known as modified Base64 for regexps: http://en.wikipedia.org/wiki/Base64#Regular_expressions
        var d = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!-";
        return d.indexOf(a)
    },
    base64BytesToIntArray: function (a) {
        for (var d = [], c, b = 0; b < a.length; b++) if (b % 2 == 0) c = 64 * this.base64ByteToInt(a.charAt(b));
        else {
            c += this.base64ByteToInt(a.charAt(b));
            d.push(c)
        }
        return d
    }
    // ...
};