com.github.mygreen.cellformatter.number.SimpleFraction Maven / Gradle / Ivy
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package com.github.mygreen.cellformatter.number;
/**
* 簡易的な分数を表現するクラス。
* 古いPOIだと提供されていないため、同じものを実装。
*
* @author T.TSUCHIE
*
*/
public class SimpleFraction {
/** 分母 */
private final int denominator;
/** 分子 */
private final int numerator;
/**
* 分子と分母を指定してインスタンスを作成する。
* @param numerator 分子。
* @param denominator 分母。
*/
public SimpleFraction(final int numerator, final int denominator) {
if(denominator == 0) {
throw new IllegalArgumentException("denominator should not be zero.");
}
this.numerator = numerator;
this.denominator = denominator;
}
/**
* 分母の値を指定してインスタンスを作成する。
*
* @param val 分数として表現するもとの数値の値。
* @param exactDenom 分母の値。
* @return
*/
public static SimpleFraction createFractionExactDenominator(final double val, final int exactDenom){
int num = (int)Math.round(val*(double)exactDenom);
return new SimpleFraction(num,exactDenom);
}
/**
* 分母の最大値を指定してインスタンスを作成する。
*
指定した分母の値以下に近似した分数を取得する。
*
* @param value 分数として表現するもとの数値の値。
* @param maxDenominator 分母の最大値。
*
* @throws RuntimeException if the continued fraction failed to converge.
* @throws IllegalArgumentException if value > Integer.MAX_VALUE
*/
public static SimpleFraction createFractionMaxDenominator(final double value, final int maxDenominator){
return buildFractionMaxDenominator(value, 0, maxDenominator, 100);
}
/**
* Create a fraction given the double value and either the maximum error
* allowed or the maximum number of denominator digits.
*
* References:
*
* -
* Continued Fraction equations (11) and (22)-(26)
*
*
*
* Based on org.apache.commons.math.fraction.Fraction from Apache Commons-Math.
* YK: The only reason of having this class is to avoid dependency on the Commons-Math jar.
*
* @param value the double value to convert to a fraction.
* @param epsilon maximum error allowed. The resulting fraction is within
* epsilon of value, in absolute terms.
* @param maxDenominator maximum denominator value allowed.
* @param maxIterations maximum number of convergents
* @throws RuntimeException if the continued fraction failed to
* converge.
* @throws IllegalArgumentException if value > Integer.MAX_VALUE
*/
private static SimpleFraction buildFractionMaxDenominator(final double value, final double epsilon,
final int maxDenominator, final int maxIterations) {
final long overflow = Integer.MAX_VALUE;
double r0 = value;
long a0 = (long)Math.floor(r0);
if (a0 > overflow) {
throw new IllegalArgumentException("Overflow trying to convert "+value+" to fraction ("+a0+"/"+1l+")");
}
// check for (almost) integer arguments, which should not go
// to iterations.
if (Math.abs(a0 - value) < epsilon) {
return new SimpleFraction((int)a0, 1);
}
long p0 = 1;
long q0 = 0;
long p1 = a0;
long q1 = 1;
long p2;
long q2;
int n = 0;
boolean stop = false;
do {
++n;
double r1 = 1.0 / (r0 - a0);
long a1 = (long)Math.floor(r1);
p2 = (a1 * p1) + p0;
q2 = (a1 * q1) + q0;
//MATH-996/POI-55419
if (epsilon == 0.0f && maxDenominator > 0 && Math.abs(q2) > maxDenominator &&
Math.abs(q1) < maxDenominator){
return new SimpleFraction((int)p1, (int)q1);
}
if ((p2 > overflow) || (q2 > overflow)) {
throw new RuntimeException("Overflow trying to convert "+value+" to fraction ("+p2+"/"+q2+")");
}
double convergent = (double)p2 / (double)q2;
if (n < maxIterations && Math.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 RuntimeException("Unable to convert "+value+" to fraction after "+maxIterations+" iterations");
}
if (q2 < maxDenominator) {
return new SimpleFraction((int) p2, (int)q2);
} else {
return new SimpleFraction((int)p1, (int)q1);
}
}
/**
* 分母の取得
*
* @return the denominator.
*/
public int getDenominator() {
return denominator;
}
/**
* 分子の取得
*
* @return the numerator.
*/
public int getNumerator() {
return numerator;
}
}