/**
* Divide the value of this fraction by another.
*
* @param fraction the fraction to divide by, must not be {@code null}
* @return a {@code Fraction} instance with the resulting values
* @throws IllegalArgumentException if the fraction is {@code null}
* @throws MathArithmeticException if the fraction to divide by is zero
* @throws MathArithmeticException if the resulting numerator or denominator exceeds {@code
* Integer.MAX_VALUE}
*/
public Fraction divide(Fraction fraction) {
if (fraction == null) {
throw new NullArgumentException(LocalizedFormats.FRACTION);
}
if (fraction.numerator == 0) {
throw new MathArithmeticException(
LocalizedFormats.ZERO_FRACTION_TO_DIVIDE_BY, fraction.numerator, fraction.denominator);
}
return multiply(fraction.reciprocal());
}
/**
* Implement add and subtract using algorithm described in Knuth 4.5.1.
*
* @param fraction the fraction to subtract, must not be {@code null}
* @param isAdd true to add, false to subtract
* @return a {@code Fraction} instance with the resulting values
* @throws NullArgumentException if the fraction is {@code null}
* @throws MathArithmeticException if the resulting numerator or denominator cannot be represented
* in an {@code int}.
*/
private Fraction addSub(Fraction fraction, boolean isAdd) {
if (fraction == null) {
throw new NullArgumentException(LocalizedFormats.FRACTION);
}
// zero is identity for addition.
if (numerator == 0) {
return isAdd ? fraction : fraction.negate();
}
if (fraction.numerator == 0) {
return this;
}
// if denominators are randomly distributed, d1 will be 1 about 61%
// of the time.
int d1 = ArithmeticUtils.gcd(denominator, fraction.denominator);
if (d1 == 1) {
// result is ( (u*v' +/- u'v) / u'v')
int uvp = ArithmeticUtils.mulAndCheck(numerator, fraction.denominator);
int upv = ArithmeticUtils.mulAndCheck(fraction.numerator, denominator);
return new Fraction(
isAdd ? ArithmeticUtils.addAndCheck(uvp, upv) : ArithmeticUtils.subAndCheck(uvp, upv),
ArithmeticUtils.mulAndCheck(denominator, fraction.denominator));
}
// the quantity 't' requires 65 bits of precision; see knuth 4.5.1
// exercise 7. we're going to use a BigInteger.
// t = u(v'/d1) +/- v(u'/d1)
BigInteger uvp =
BigInteger.valueOf(numerator).multiply(BigInteger.valueOf(fraction.denominator / d1));
BigInteger upv =
BigInteger.valueOf(fraction.numerator).multiply(BigInteger.valueOf(denominator / d1));
BigInteger t = isAdd ? uvp.add(upv) : uvp.subtract(upv);
// but d2 doesn't need extra precision because
// d2 = gcd(t,d1) = gcd(t mod d1, d1)
int tmodd1 = t.mod(BigInteger.valueOf(d1)).intValue();
int d2 = (tmodd1 == 0) ? d1 : ArithmeticUtils.gcd(tmodd1, d1);
// result is (t/d2) / (u'/d1)(v'/d2)
BigInteger w = t.divide(BigInteger.valueOf(d2));
if (w.bitLength() > 31) {
throw new MathArithmeticException(LocalizedFormats.NUMERATOR_OVERFLOW_AFTER_MULTIPLY, w);
}
return new Fraction(
w.intValue(), ArithmeticUtils.mulAndCheck(denominator / d1, fraction.denominator / d2));
}
