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With inspiration from other libraries
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.math3.fraction;
import java.io.Serializable;
import java.math.BigInteger;
import org.apache.commons.math3.FieldElement;
import org.apache.commons.math3.exception.util.LocalizedFormats;
import org.apache.commons.math3.exception.MathArithmeticException;
import org.apache.commons.math3.exception.NullArgumentException;
import org.apache.commons.math3.util.ArithmeticUtils;
import org.apache.commons.math3.util.FastMath;
/**
* Representation of a rational number.
*
* implements Serializable since 2.0
*
* @since 1.1
*/
public class Fraction
extends Number
implements FieldElement, Comparable, Serializable {
/** A fraction representing "2 / 1". */
public static final Fraction TWO = new Fraction(2, 1);
/** A fraction representing "1". */
public static final Fraction ONE = new Fraction(1, 1);
/** A fraction representing "0". */
public static final Fraction ZERO = new Fraction(0, 1);
/** A fraction representing "4/5". */
public static final Fraction FOUR_FIFTHS = new Fraction(4, 5);
/** A fraction representing "1/5". */
public static final Fraction ONE_FIFTH = new Fraction(1, 5);
/** A fraction representing "1/2". */
public static final Fraction ONE_HALF = new Fraction(1, 2);
/** A fraction representing "1/4". */
public static final Fraction ONE_QUARTER = new Fraction(1, 4);
/** A fraction representing "1/3". */
public static final Fraction ONE_THIRD = new Fraction(1, 3);
/** A fraction representing "3/5". */
public static final Fraction THREE_FIFTHS = new Fraction(3, 5);
/** A fraction representing "3/4". */
public static final Fraction THREE_QUARTERS = new Fraction(3, 4);
/** A fraction representing "2/5". */
public static final Fraction TWO_FIFTHS = new Fraction(2, 5);
/** A fraction representing "2/4". */
public static final Fraction TWO_QUARTERS = new Fraction(2, 4);
/** A fraction representing "2/3". */
public static final Fraction TWO_THIRDS = new Fraction(2, 3);
/** A fraction representing "-1 / 1". */
public static final Fraction MINUS_ONE = new Fraction(-1, 1);
/** Serializable version identifier */
private static final long serialVersionUID = 3698073679419233275L;
/** The default epsilon used for convergence. */
private static final double DEFAULT_EPSILON = 1e-5;
/** The denominator. */
private final int denominator;
/** The numerator. */
private final int numerator;
/**
* Create a fraction given the double value.
* @param value the double value to convert to a fraction.
* @throws FractionConversionException if the continued fraction failed to
* converge.
*/
public Fraction(double value) throws FractionConversionException {
this(value, DEFAULT_EPSILON, 100);
}
/**
* Create a fraction given the double value and maximum error allowed.
*
* References:
*
* -
* Continued Fraction equations (11) and (22)-(26)
*
*
* @param value the double value to convert to a fraction.
* @param epsilon maximum error allowed. The resulting fraction is within
* {@code epsilon} of {@code value}, in absolute terms.
* @param maxIterations maximum number of convergents
* @throws FractionConversionException if the continued fraction failed to
* converge.
*/
public Fraction(double value, double epsilon, int maxIterations)
throws FractionConversionException
{
this(value, epsilon, Integer.MAX_VALUE, maxIterations);
}
/**
* Create a fraction given the double value and maximum denominator.
*
* References:
*
* -
* Continued Fraction equations (11) and (22)-(26)
*
*
* @param value the double value to convert to a fraction.
* @param maxDenominator The maximum allowed value for denominator
* @throws FractionConversionException if the continued fraction failed to
* converge
*/
public Fraction(double value, int maxDenominator)
throws FractionConversionException
{
this(value, 0, maxDenominator, 100);
}
/**
* Create a fraction given the double value and either the maximum error
* allowed or the maximum number of denominator digits.
*
*
* NOTE: This constructor is called with EITHER
* - a valid epsilon value and the maxDenominator set to Integer.MAX_VALUE
* (that way the maxDenominator has no effect).
* OR
* - a valid maxDenominator value and the epsilon value set to zero
* (that way epsilon only has effect if there is an exact match before
* the maxDenominator value is reached).
*
*
* It has been done this way so that the same code can be (re)used for both
* scenarios. However this could be confusing to users if it were part of
* the public API and this constructor should therefore remain PRIVATE.
*
*
* See JIRA issue ticket MATH-181 for more details:
*
* https://issues.apache.org/jira/browse/MATH-181
*
* @param value the double value to convert to a fraction.
* @param epsilon maximum error allowed. The resulting fraction is within
* {@code epsilon} of {@code value}, in absolute terms.
* @param maxDenominator maximum denominator value allowed.
* @param maxIterations maximum number of convergents
* @throws FractionConversionException if the continued fraction failed to
* converge.
*/
private Fraction(double value, double epsilon, int maxDenominator, int maxIterations)
throws FractionConversionException
{
long overflow = Integer.MAX_VALUE;
double r0 = value;
long a0 = (long)FastMath.floor(r0);
if (FastMath.abs(a0) > overflow) {
throw new FractionConversionException(value, a0, 1l);
}
// check for (almost) integer arguments, which should not go to iterations.
if (FastMath.abs(a0 - value) < epsilon) {
this.numerator = (int) a0;
this.denominator = 1;
return;
}
long p0 = 1;
long q0 = 0;
long p1 = a0;
long q1 = 1;
long p2 = 0;
long q2 = 1;
int n = 0;
boolean stop = false;
do {
++n;
double r1 = 1.0 / (r0 - a0);
long a1 = (long)FastMath.floor(r1);
p2 = (a1 * p1) + p0;
q2 = (a1 * q1) + q0;
if ((FastMath.abs(p2) > overflow) || (FastMath.abs(q2) > overflow)) {
// in maxDenominator mode, if the last fraction was very close to the actual value
// q2 may overflow in the next iteration; in this case return the last one.
if (epsilon == 0.0 && FastMath.abs(q1) < maxDenominator) {
break;
}
throw new FractionConversionException(value, p2, q2);
}
double convergent = (double)p2 / (double)q2;
if (n < maxIterations && FastMath.abs(convergent - value) > epsilon && q2 < maxDenominator) {
p0 = p1;
p1 = p2;
q0 = q1;
q1 = q2;
a0 = a1;
r0 = r1;
} else {
stop = true;
}
} while (!stop);
if (n >= maxIterations) {
throw new FractionConversionException(value, maxIterations);
}
if (q2 < maxDenominator) {
this.numerator = (int) p2;
this.denominator = (int) q2;
} else {
this.numerator = (int) p1;
this.denominator = (int) q1;
}
}
/**
* Create a fraction from an int.
* The fraction is num / 1.
* @param num the numerator.
*/
public Fraction(int num) {
this(num, 1);
}
/**
* Create a fraction given the numerator and denominator. The fraction is
* reduced to lowest terms.
* @param num the numerator.
* @param den the denominator.
* @throws MathArithmeticException if the denominator is {@code zero}
*/
public Fraction(int num, int den) {
if (den == 0) {
throw new MathArithmeticException(LocalizedFormats.ZERO_DENOMINATOR_IN_FRACTION,
num, den);
}
if (den < 0) {
if (num == Integer.MIN_VALUE ||
den == Integer.MIN_VALUE) {
throw new MathArithmeticException(LocalizedFormats.OVERFLOW_IN_FRACTION,
num, den);
}
num = -num;
den = -den;
}
// reduce numerator and denominator by greatest common denominator.
final int d = ArithmeticUtils.gcd(num, den);
if (d > 1) {
num /= d;
den /= d;
}
// move sign to numerator.
if (den < 0) {
num = -num;
den = -den;
}
this.numerator = num;
this.denominator = den;
}
/**
* Returns the absolute value of this fraction.
* @return the absolute value.
*/
public Fraction abs() {
Fraction ret;
if (numerator >= 0) {
ret = this;
} else {
ret = negate();
}
return ret;
}
/**
* Compares this object to another based on size.
* @param object the object to compare to
* @return -1 if this is less than {@code object}, +1 if this is greater
* than {@code object}, 0 if they are equal.
*/
public int compareTo(Fraction object) {
long nOd = ((long) numerator) * object.denominator;
long dOn = ((long) denominator) * object.numerator;
return (nOd < dOn) ? -1 : ((nOd > dOn) ? +1 : 0);
}
/**
* Gets the fraction as a {@code double}. This calculates the fraction as
* the numerator divided by denominator.
* @return the fraction as a {@code double}
*/
@Override
public double doubleValue() {
return (double)numerator / (double)denominator;
}
/**
* Test for the equality of two fractions. If the lowest term
* numerator and denominators are the same for both fractions, the two
* fractions are considered to be equal.
* @param other fraction to test for equality to this fraction
* @return true if two fractions are equal, false if object is
* {@code null}, not an instance of {@link Fraction}, or not equal
* to this fraction instance.
*/
@Override
public boolean equals(Object other) {
if (this == other) {
return true;
}
if (other instanceof Fraction) {
// since fractions are always in lowest terms, numerators and
// denominators can be compared directly for equality.
Fraction rhs = (Fraction)other;
return (numerator == rhs.numerator) &&
(denominator == rhs.denominator);
}
return false;
}
/**
* Gets the fraction as a {@code float}. This calculates the fraction as
* the numerator divided by denominator.
* @return the fraction as a {@code float}
*/
@Override
public float floatValue() {
return (float)doubleValue();
}
/**
* Access the denominator.
* @return the denominator.
*/
public int getDenominator() {
return denominator;
}
/**
* Access the numerator.
* @return the numerator.
*/
public int getNumerator() {
return numerator;
}
/**
* Gets a hashCode for the fraction.
* @return a hash code value for this object
*/
@Override
public int hashCode() {
return 37 * (37 * 17 + numerator) + denominator;
}
/**
* Gets the fraction as an {@code int}. This returns the whole number part
* of the fraction.
* @return the whole number fraction part
*/
@Override
public int intValue() {
return (int)doubleValue();
}
/**
* Gets the fraction as a {@code long}. This returns the whole number part
* of the fraction.
* @return the whole number fraction part
*/
@Override
public long longValue() {
return (long)doubleValue();
}
/**
* Return the additive inverse of this fraction.
* @return the negation of this fraction.
*/
public Fraction negate() {
if (numerator==Integer.MIN_VALUE) {
throw new MathArithmeticException(LocalizedFormats.OVERFLOW_IN_FRACTION, numerator, denominator);
}
return new Fraction(-numerator, denominator);
}
/**
* Return the multiplicative inverse of this fraction.
* @return the reciprocal fraction
*/
public Fraction reciprocal() {
return new Fraction(denominator, numerator);
}
/**
* Adds the value of this fraction to another, returning the result in reduced form.
* The algorithm follows Knuth, 4.5.1.
*
* @param fraction the fraction to add, must not be {@code null}
* @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 exceeds
* {@code Integer.MAX_VALUE}
*/
public Fraction add(Fraction fraction) {
return addSub(fraction, true /* add */);
}
/**
* Add an integer to the fraction.
* @param i the {@code integer} to add.
* @return this + i
*/
public Fraction add(final int i) {
return new Fraction(numerator + i * denominator, denominator);
}
/**
* Subtracts the value of another fraction from the value of this one,
* returning the result in reduced form.
*
* @param fraction the fraction to subtract, must not be {@code null}
* @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}.
*/
public Fraction subtract(Fraction fraction) {
return addSub(fraction, false /* subtract */);
}
/**
* Subtract an integer from the fraction.
* @param i the {@code integer} to subtract.
* @return this - i
*/
public Fraction subtract(final int i) {
return new Fraction(numerator - i * denominator, denominator);
}
/**
* 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));
}
/**
* Multiplies the value of this fraction by another, returning the
* result in reduced form.
*
* @param fraction the fraction to multiply by, must not be {@code null}
* @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 exceeds
* {@code Integer.MAX_VALUE}
*/
public Fraction multiply(Fraction fraction) {
if (fraction == null) {
throw new NullArgumentException(LocalizedFormats.FRACTION);
}
if (numerator == 0 || fraction.numerator == 0) {
return ZERO;
}
// knuth 4.5.1
// make sure we don't overflow unless the result *must* overflow.
int d1 = ArithmeticUtils.gcd(numerator, fraction.denominator);
int d2 = ArithmeticUtils.gcd(fraction.numerator, denominator);
return getReducedFraction
(ArithmeticUtils.mulAndCheck(numerator/d1, fraction.numerator/d2),
ArithmeticUtils.mulAndCheck(denominator/d2, fraction.denominator/d1));
}
/**
* Multiply the fraction by an integer.
* @param i the {@code integer} to multiply by.
* @return this * i
*/
public Fraction multiply(final int i) {
return multiply(new Fraction(i));
}
/**
* 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());
}
/**
* Divide the fraction by an integer.
* @param i the {@code integer} to divide by.
* @return this * i
*/
public Fraction divide(final int i) {
return divide(new Fraction(i));
}
/**
*
* Gets the fraction percentage as a {@code double}. This calculates the
* fraction as the numerator divided by denominator multiplied by 100.
*
*
* @return the fraction percentage as a {@code double}.
*/
public double percentageValue() {
return 100 * doubleValue();
}
/**
* Creates a {@code Fraction} instance with the 2 parts
* of a fraction Y/Z.
*
* Any negative signs are resolved to be on the numerator.
*
* @param numerator the numerator, for example the three in 'three sevenths'
* @param denominator the denominator, for example the seven in 'three sevenths'
* @return a new fraction instance, with the numerator and denominator reduced
* @throws MathArithmeticException if the denominator is {@code zero}
*/
public static Fraction getReducedFraction(int numerator, int denominator) {
if (denominator == 0) {
throw new MathArithmeticException(LocalizedFormats.ZERO_DENOMINATOR_IN_FRACTION,
numerator, denominator);
}
if (numerator==0) {
return ZERO; // normalize zero.
}
// allow 2^k/-2^31 as a valid fraction (where k>0)
if (denominator==Integer.MIN_VALUE && (numerator&1)==0) {
numerator/=2; denominator/=2;
}
if (denominator < 0) {
if (numerator==Integer.MIN_VALUE ||
denominator==Integer.MIN_VALUE) {
throw new MathArithmeticException(LocalizedFormats.OVERFLOW_IN_FRACTION,
numerator, denominator);
}
numerator = -numerator;
denominator = -denominator;
}
// simplify fraction.
int gcd = ArithmeticUtils.gcd(numerator, denominator);
numerator /= gcd;
denominator /= gcd;
return new Fraction(numerator, denominator);
}
/**
*
* Returns the {@code String} representing this fraction, ie
* "num / dem" or just "num" if the denominator is one.
*
*
* @return a string representation of the fraction.
* @see java.lang.Object#toString()
*/
@Override
public String toString() {
String str = null;
if (denominator == 1) {
str = Integer.toString(numerator);
} else if (numerator == 0) {
str = "0";
} else {
str = numerator + " / " + denominator;
}
return str;
}
/** {@inheritDoc} */
public FractionField getField() {
return FractionField.getInstance();
}
}