xsheetjs/bits/30_frac.js

function frac(x/*:number*/, D/*:number*/, mixed/*:?boolean*/)/*:Array<number>*/ {
	var sgn = x < 0 ? -1 : 1;
	var B = x * sgn;
	var P_2 = 0, P_1 = 1, P = 0;
	var Q_2 = 1, Q_1 = 0, Q = 0;
	var A = Math.floor(B);
	while(Q_1 < D) {
		A = Math.floor(B);
		P = A * P_1 + P_2;
		Q = A * Q_1 + Q_2;
		if((B - A) < 0.00000005) break;
		B = 1 / (B - A);
		P_2 = P_1; P_1 = P;
		Q_2 = Q_1; Q_1 = Q;
	}
	if(Q > D) { if(Q_1 > D) { Q = Q_2; P = P_2; } else { Q = Q_1; P = P_1; } }
	if(!mixed) return [0, sgn * P, Q];
	var q = Math.floor(sgn * P/Q);
	return [q, sgn*P - q*Q, Q];
}