Polynom operations

poly

var a = "5x^5+3x^3-7x^2+4x+30";
var b = "8x^5+4x^4-2x^3-2x^2+4x";

function secti(a, b) {
	var koefA = getKoef(a);
	var koefB = getKoef(b);
	var res = '', tmp;
	for (var i=Math.max(koefA.length, koefB.length); i--;) {
		if (koefA[i] && koefB[i] && (koefA[i] || 0) + (koefB[i] || 0)) {
			tmp = koefA[i] + koefB[i];
			res += (tmp >=0 ? '+' + tmp : tmp) + (i > 0 ? 'x' : '');
			if (i>1) {
				res += '^'+i;
			}
		} else if (tmp = (koefA[i] || koefB[i]) && (koefA[i] || 0) + (koefB[i] || 0)) {
			res += (tmp >=0 ? '+' + tmp : tmp) + (i > 0 ? 'x' : '');
			if (i>1) {
				res += '^'+i;
			}
		}
	}
	return res;
}

function getKoef(a) {
	var koef = [];
	var tmpKoef = '';
	var tmpIndex = '';
	var role = 0;
	var tmpIndexInt;
	for (var i=0, j=a.length;i<j;i++) {
		if (a[i] == '-' || a[i] == '+') {
			if (tmpKoef) {
				tmpIndexInt = parseInt(tmpIndex) || 1;
				koef[tmpIndexInt] = (koef[tmpIndexInt] || 0) + parseInt(tmpKoef);
				tmpIndex = '';
				tmpKoef = '';
			}
			role = 0;
		}
		if (parseInt(a[i]) == a[i] || a[i] == '-') {
			if (role == 0) {
				tmpKoef += a[i];
			} else {
				tmpIndex += a[i]
			}
		} else if (a[i] == 'x') {
			role = 1;
		} 
	}
	if (tmpKoef) {
		koef[0] = parseInt(tmpKoef);
	}
	return koef;
}

alert(secti(a, b));