Fraction: Optimise divide by fraction
The divide uses multiply by reciprocal. This can avoid the call to
reciprocal() by directly inverting the numerator and denominator. These
will already by in reduced form and thus this avoids the reduction
algorithm.
diff --git a/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/BigFraction.java b/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/BigFraction.java
index 6a16541..6e1ea48 100644
--- a/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/BigFraction.java
+++ b/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/BigFraction.java
@@ -913,7 +913,9 @@
if (isZero()) {
return ZERO;
}
- return multiply(value.reciprocal());
+ // Multiply by reciprocal
+ return new BigFraction(numerator.multiply(value.denominator),
+ denominator.multiply(value.numerator));
}
/**
diff --git a/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/Fraction.java b/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/Fraction.java
index d424045..6702950 100644
--- a/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/Fraction.java
+++ b/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/Fraction.java
@@ -615,13 +615,29 @@
if (value.isZero() || isZero()) {
return ZERO;
}
+ return multiply(value.numerator, value.denominator);
+ }
+ /**
+ * Multiply this fraction by the passed fraction decomposed into a numerator and
+ * denominator, returning the result in reduced form.
+ *
+ * <p>This is a utility method to be used by multiply and divide. The decomposed
+ * fraction arguments and this fraction are not checked for zero.
+ *
+ * @param num Fraction numerator.
+ * @param den Fraction denominator.
+ * @return {@code this * num / den}.
+ * @throws ArithmeticException if the resulting numerator or denominator cannot
+ * be represented in an {@code int}.
+ */
+ private Fraction multiply(int num, int den) {
// knuth 4.5.1
// Make sure we don't overflow unless the result *must* overflow.
- final int d1 = ArithmeticUtils.gcd(numerator, value.denominator);
- final int d2 = ArithmeticUtils.gcd(value.numerator, denominator);
- return new Fraction(Math.multiplyExact(numerator / d1, value.numerator / d2),
- Math.multiplyExact(denominator / d2, value.denominator / d1));
+ final int d1 = ArithmeticUtils.gcd(numerator, den);
+ final int d2 = ArithmeticUtils.gcd(num, denominator);
+ return new Fraction(Math.multiplyExact(numerator / d1, num / d2),
+ Math.multiplyExact(denominator / d2, den / d1));
}
/**
@@ -669,7 +685,8 @@
if (isZero()) {
return ZERO;
}
- return multiply(value.reciprocal());
+ // Multiply by reciprocal
+ return multiply(value.denominator, value.numerator);
}
/**
