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Added support for sqrt and 1/x
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@javadev
javadev committed Jan 26, 2013
1 parent b7e93c8 commit 06dd011
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253 changes: 253 additions & 0 deletions checkstyle.xml
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2 changes: 2 additions & 0 deletions pom.xml
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Expand All @@ -23,6 +24,7 @@
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60 changes: 60 additions & 0 deletions src/main/java/com/github/calc/BigDecimalUtil.java
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/*
* $Id$
*
* Copyright 2013 Valentyn Kolesnikov
*
* Licensed 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 com.github.calc;

import java.math.BigDecimal;
import java.math.BigInteger;

public class BigDecimalUtil {

/**
* Compute the square root of x to a given scale, x >= 0.
* Use Newton's algorithm.
* @param x the value of x
* @param scale the desired scale of the result
* @return the result value
*/
public static BigDecimal sqrt(BigDecimal x) {
int scale = 18;
// Check that x >= 0.
if (x.signum() < 0) {
throw new ArithmeticException("x < 0");
}

// n = x*(10^(2*scale))
BigInteger n = x.movePointRight(scale << 1).toBigInteger();

// The first approximation is the upper half of n.
int bits = (n.bitLength() + 1) >> 1;
BigInteger ix = n.shiftRight(bits);
BigInteger ixPrev;

// Loop until the approximations converge
// (two successive approximations are equal after rounding).
do {
ixPrev = ix;

// x = (x + n/x)/2
ix = ix.add(n.divide(ix)).shiftRight(1);

Thread.yield();
} while (ix.compareTo(ixPrev) != 0);

return new BigDecimal(ix, scale);
}
}
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