fix: limitDenominator crashing

Sources/RationalModule/Rational.swift

@@ -166,15 +166,15 @@ extension Rational {
 		var d = denominator
 
 		while true {
-			let a = n / d
+			let a = floorDivision(n, d)
 			let q2 = q0 + a * q1
 			guard q2 <= max else { break }
 
 			(p0, q0, p1, q1) = (p1, q1, p0 + a * p1, q2)
 			(n, d) = (d, n - a * d)
 		}
 
-		let k = (max - q0) / q1
+		let k = floorDivision((max - q0), q1)
 		return if 2 * d * (q0 + k * q1) <= denominator {
 			Self(numerator: p1, denominator: q1)
 		} else {
@@ -183,6 +183,17 @@ extension Rational {
 	}
 }
 
+/// Equivalent to Python's `//` operator.
+@usableFromInline
+internal func floorDivision<T: BinaryInteger>(_ a: T, _ b: T) -> T {
+	let quotient = a / b
+	return if a >= 0 {
+		quotient
+	} else {
+		quotient - 1
+	}
+}
+
 // MARK: - Rounding
 extension Rational {
 	/// The greatest integer less than or equal to this value.