BigInteger bitwise Gcd : BigInteger « Data Type « Java

1. Java
2. Data Type
3. BigInteger

BigInteger bitwise Gcd

 

/*
 * @(#)MathUtil.java  1.0 Apr 26, 2008
 *
 *  The MIT License
 *
 *  Copyright (c) 2008 Malachi de AElfweald <malachid@gmail.com>
 *
 *  Permission is hereby granted, free of charge, to any person obtaining a copy
 *  of this software and associated documentation files (the "Software"), to deal
 *  in the Software without restriction, including without limitation the rights
 *  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 *  copies of the Software, and to permit persons to whom the Software is
 *  furnished to do so, subject to the following conditions:
 *
 *  The above copyright notice and this permission notice shall be included in
 *  all copies or substantial portions of the Software.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 *  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 *  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 *  THE SOFTWARE.
 */
 
 
import java.math.BigDecimal;
import java.math.BigInteger;
import java.math.RoundingMode;



public class Util{
  protected static BigInteger BigIntegerZERO = BigInteger.ZERO;
  protected static BigInteger BigIntegerONE = BigInteger.ONE;
  protected static BigInteger BigIntegerTWO = BigInteger.valueOf(2);
  protected static BigInteger BigIntegerTHREE=BigInteger.valueOf(3);
  protected static BigInteger FactorialBreakpoint = BigInteger.valueOf(96);
  protected static BigDecimal BigDecimalZERO = BigDecimal.ZERO;
  protected static BigDecimal BigDecimalONE = BigDecimal.ONE;
  protected static BigDecimal BigDecimalTWO = new BigDecimal(2);
  protected static BigDecimal BigDecimalFOUR = new BigDecimal(4);
  
  public static BigInteger bitwiseGcd(BigInteger u, BigInteger v)
  {
    if(u.equals(BigInteger.ZERO)) return v;
    if(v.equals(BigInteger.ZERO)) return u;

//    System.out.format("u=%s=%s\nu.getLowestSetBit()=%s\n%s>>%s=%s = %s\n", u, u.toString(2), u.getLowestSetBit(), u, u.getLowestSetBit(), u.shiftRight(u.getLowestSetBit()), u.shiftRight(u.getLowestSetBit()).toString(2));

    int uBit = u.getLowestSetBit();
    int vBit = v.getLowestSetBit();
    int k = (uBit <= vBit ? uBit : vBit);

    while(u.signum() > 0)
    {
      // first ensure that both are odd
      u = u.shiftRight(u.getLowestSetBit());
      v = v.shiftRight(v.getLowestSetBit());
      if(u.subtract(v).signum() >= 0)
      {
        u = (u.subtract(v)).shiftRight(1);
      }else{
        v = (v.subtract(u)).shiftRight(1);
      }
    }

    return v.shiftLeft(k);
  }
}

   
  

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