JavaScript function to compose coordinates of svg path to represent a star

d3star.js

/**
 * Compose coordinates of svg path to represent a star
 * @param int size
 * @return string
 */
var d3_star = function (size) {
    
    var d18 = Math.PI / 10,
        d36 = d18 * 2,
        sind18 = Math.sin(d18),
        cosd18 = Math.cos(d18),
        tand18 = sind18 / cosd18,
        sind36 = Math.sin(d36),
        cosd36 = Math.cos(d36),
        tand36 = sind36 / cosd36;
    
    var a = Math.sqrt(size / (5 * tand18 * (1 + tand18 / tand36))),
        b = a * tand18 / tand36,
        c = a * tand18,
        d = Math.sqrt(a * a + c * c),
        e = Math.sqrt(b * b + c * c),
        ab = a + b,
        cd = c + d;
    
    return 'M0,' + -ab +
        'L' + c + ',' + -b +
        ' ' + cd + ',' + -b +
        ' ' + e * cosd18 + ',' + e * sind18 +
        ' ' + ab * sind36 + ',' + ab * cosd36 +
        ' 0,' + e +
        ' ' + -ab * sind36 + ',' + ab * cosd36 +
        ' ' + -e * cosd18 + ',' + e * sind18 +
        ' ' + -cd + ',' + -b +
        ' ' + -c + ',' + -b +
        'Z';
};