libcore/math/src/test/java/org/apache/harmony/math/tests/java/math/BigIntegerModPowTest.java - platform/dalvik - Git at Google

 /*
  *  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.
  */
 /**
  * @author Elena Semukhina
  * @version $Revision$
  */

 package org.apache.harmony.math.tests.java.math;

 import java.math.BigInteger;

 import junit.framework.TestCase;

 /**
  * Class:   java.math.BigInteger
  * Methods: modPow, modInverse, and gcd
  */
 public class BigIntegerModPowTest extends TestCase {
     /**
      * modPow: non-positive modulus
      */
     public void testModPowException() {
         byte aBytes[] = {1, 2, 3, 4, 5, 6, 7};
         byte eBytes[] = {1, 2, 3, 4, 5};
         byte mBytes[] = {1, 2, 3};
         int aSign = 1;
         int eSign = 1;
         int mSign = -1;
         BigInteger aNumber = new BigInteger(aSign, aBytes);
         BigInteger exp = new BigInteger(eSign, eBytes);
         BigInteger modulus = new BigInteger(mSign, mBytes);
         try {
             aNumber.modPow(exp, modulus);
             fail("ArithmeticException has not been caught");
         } catch (ArithmeticException e) {
             assertEquals("Improper exception message", "BigInteger: modulus not positive", e.getMessage());
         }
     }

     /**
      * modPow: positive exponent
      */
     public void testModPowPosExp() {
         byte aBytes[] = {-127, 100, 56, 7, 98, -1, 39, -128, 127, 75, 48, -7};
         byte eBytes[] = {27, -15, 65, 39};
         byte mBytes[] = {-128, 2, 3, 4, 5};
         int aSign = 1;
         int eSign = 1;
         int mSign = 1;
         byte rBytes[] = {113, 100, -84, -28, -85};
         BigInteger aNumber = new BigInteger(aSign, aBytes);
         BigInteger exp =      new BigInteger(eSign, eBytes);
         BigInteger modulus = new BigInteger(mSign, mBytes);
         BigInteger result = aNumber.modPow(exp, modulus);
         byte resBytes[] = new byte[rBytes.length];
         resBytes = result.toByteArray();
         for(int i = 0; i < resBytes.length; i++) {
             assertTrue(resBytes[i] == rBytes[i]);
         }
         assertEquals("incorrect sign", 1, result.signum());
     }

     /**
      * modPow: negative exponent
      */
     public void testModPowNegExp() {
         byte aBytes[] = {-127, 100, 56, 7, 98, -1, 39, -128, 127, 75, 48, -7};
         byte eBytes[] = {27, -15, 65, 39};
         byte mBytes[] = {-128, 2, 3, 4, 5};
         int aSign = 1;
         int eSign = -1;
         int mSign = 1;
         byte rBytes[] = {12, 118, 46, 86, 92};
         BigInteger aNumber = new BigInteger(aSign, aBytes);
         BigInteger exp =      new BigInteger(eSign, eBytes);
         BigInteger modulus = new BigInteger(mSign, mBytes);
         BigInteger result = aNumber.modPow(exp, modulus);
         byte resBytes[] = new byte[rBytes.length];
         resBytes = result.toByteArray();
         for(int i = 0; i < resBytes.length; i++) {
             assertTrue(resBytes[i] == rBytes[i]);
         }
         assertEquals("incorrect sign", 1, result.signum());
     }

     /**
      * modInverse: non-positive modulus
      */
     public void testmodInverseException() {
         byte aBytes[] = {1, 2, 3, 4, 5, 6, 7};
         byte mBytes[] = {1, 2, 3};
         int aSign = 1;
         int mSign = -1;
         BigInteger aNumber = new BigInteger(aSign, aBytes);
         BigInteger modulus = new BigInteger(mSign, mBytes);
         try {
             aNumber.modInverse(modulus);
             fail("ArithmeticException has not been caught");
         } catch (ArithmeticException e) {
             assertEquals("Improper exception message", "BigInteger: modulus not positive", e.getMessage());
         }
     }

     /**
      * modInverse: non-invertible number
      */
     public void testmodInverseNonInvertible() {
         byte aBytes[] = {-15, 24, 123, 56, -11, -112, -34, -98, 8, 10, 12, 14, 25, 125, -15, 28, -127};
         byte mBytes[] = {-12, 1, 0, 0, 0, 23, 44, 55, 66};
         int aSign = 1;
         int mSign = 1;
         BigInteger aNumber = new BigInteger(aSign, aBytes);
         BigInteger modulus = new BigInteger(mSign, mBytes);
         try {
             aNumber.modInverse(modulus);
             fail("ArithmeticException has not been caught");
         } catch (ArithmeticException e) {
             assertEquals("Improper exception message", "BigInteger not invertible.", e.getMessage());
         }
     }

     /**
      * modInverse: positive number
      */
     public void testmodInversePos1() {
         byte aBytes[] = {24, 123, 56, -11, -112, -34, -98, 8, 10, 12, 14, 25, 125, -15, 28, -127};
         byte mBytes[] = {122, 45, 36, 100, 122, 45};
         int aSign = 1;
         int mSign = 1;
         byte rBytes[] = {47, 3, 96, 62, 87, 19};
         BigInteger aNumber = new BigInteger(aSign, aBytes);
         BigInteger modulus = new BigInteger(mSign, mBytes);
         BigInteger result = aNumber.modInverse(modulus);
         byte resBytes[] = new byte[rBytes.length];
         resBytes = result.toByteArray();
         for(int i = 0; i < resBytes.length; i++) {
             assertTrue(resBytes[i] == rBytes[i]);
         }
         assertEquals("incorrect sign", 1, result.signum());
     }

     /**
      * modInverse: positive number (another case: a < 0)
      */
     public void testmodInversePos2() {
         byte aBytes[] = {15, 24, 123, 56, -11, -112, -34, -98, 8, 10, 12, 14, 25, 125, -15, 28, -127};
         byte mBytes[] = {2, 122, 45, 36, 100};
         int aSign = 1;
         int mSign = 1;
         byte rBytes[] = {1, -93, 40, 127, 73};
         BigInteger aNumber = new BigInteger(aSign, aBytes);
         BigInteger modulus = new BigInteger(mSign, mBytes);
         BigInteger result = aNumber.modInverse(modulus);
         byte resBytes[] = new byte[rBytes.length];
         resBytes = result.toByteArray();
         for(int i = 0; i < resBytes.length; i++) {
             assertTrue(resBytes[i] == rBytes[i]);
         }
         assertEquals("incorrect sign", 1, result.signum());
     }

     /**
      * modInverse: negative number
      */
     public void testmodInverseNeg1() {
         byte aBytes[] = {15, 24, 123, 56, -11, -112, -34, -98, 8, 10, 12, 14, 25, 125, -15, 28, -127};
         byte mBytes[] = {2, 122, 45, 36, 100};
         int aSign = -1;
         int mSign = 1;
         byte rBytes[] = {0, -41, 4, -91, 27};
         BigInteger aNumber = new BigInteger(aSign, aBytes);
         BigInteger modulus = new BigInteger(mSign, mBytes);
         BigInteger result = aNumber.modInverse(modulus);
         byte resBytes[] = new byte[rBytes.length];
         resBytes = result.toByteArray();
         for(int i = 0; i < resBytes.length; i++) {
             assertTrue(resBytes[i] == rBytes[i]);
         }
         assertEquals("incorrect sign", 1, result.signum());
     }

     /**
      * modInverse: negative number (another case: x < 0)
      */
     public void testmodInverseNeg2() {
         byte aBytes[] = {-15, 24, 123, 57, -15, 24, 123, 57, -15, 24, 123, 57};
         byte mBytes[] = {122, 2, 4, 122, 2, 4};
         byte rBytes[] = {85, 47, 127, 4, -128, 45};
         BigInteger aNumber = new BigInteger(aBytes);
         BigInteger modulus = new BigInteger(mBytes);
         BigInteger result = aNumber.modInverse(modulus);
         byte resBytes[] = new byte[rBytes.length];
         resBytes = result.toByteArray();
         for(int i = 0; i < resBytes.length; i++) {
             assertTrue(resBytes[i] == rBytes[i]);
         }
         assertEquals("incorrect sign", 1, result.signum());
     }

     /**
      * gcd: the second number is zero
      */
     public void testGcdSecondZero() {
         byte aBytes[] = {15, 24, 123, 57, -15, 24, 123, 57, -15, 24, 123, 57};
         byte bBytes[] = {0};
         int aSign = 1;
         int bSign = 1;
         byte rBytes[] = {15, 24, 123, 57, -15, 24, 123, 57, -15, 24, 123, 57};
         BigInteger aNumber = new BigInteger(aSign, aBytes);
         BigInteger bNumber = new BigInteger(bSign, bBytes);
         BigInteger result = aNumber.gcd(bNumber);
         byte resBytes[] = new byte[rBytes.length];
         resBytes = result.toByteArray();
         for(int i = 0; i < resBytes.length; i++) {
             assertTrue(resBytes[i] == rBytes[i]);
         }
         assertEquals("incorrect sign", 1, result.signum());
     }

     /**
      * gcd: the first number is zero
      */
     public void testGcdFirstZero() {
         byte aBytes[] = {0};
         byte bBytes[] = {15, 24, 123, 57, -15, 24, 123, 57, -15, 24, 123, 57};
         int aSign = 1;
         int bSign = 1;
         byte rBytes[] = {15, 24, 123, 57, -15, 24, 123, 57, -15, 24, 123, 57};
         BigInteger aNumber = new BigInteger(aSign, aBytes);
         BigInteger bNumber = new BigInteger(bSign, bBytes);
         BigInteger result = aNumber.gcd(bNumber);
         byte resBytes[] = new byte[rBytes.length];
         resBytes = result.toByteArray();
         for(int i = 0; i < resBytes.length; i++) {
             assertTrue(resBytes[i] == rBytes[i]);
         }
         assertEquals("incorrect sign", 1, result.signum());
     }

     /**
      * gcd: the first number is ZERO
      */
     public void testGcdFirstZERO() {
         byte bBytes[] = {15, 24, 123, 57, -15, 24, 123, 57, -15, 24, 123, 57};
         int bSign = 1;
         byte rBytes[] = {15, 24, 123, 57, -15, 24, 123, 57, -15, 24, 123, 57};
         BigInteger aNumber = BigInteger.ZERO;
         BigInteger bNumber = new BigInteger(bSign, bBytes);
         BigInteger result = aNumber.gcd(bNumber);
         byte resBytes[] = new byte[rBytes.length];
         resBytes = result.toByteArray();
         for(int i = 0; i < resBytes.length; i++) {
             assertTrue(resBytes[i] == rBytes[i]);
         }
         assertEquals("incorrect sign", 1, result.signum());
     }

     /**
      * gcd: both numbers are zeros
      */
     public void testGcdBothZeros() {
         byte rBytes[] = {0};
         BigInteger aNumber = new BigInteger("0");
         BigInteger bNumber = BigInteger.valueOf(0L);
         BigInteger result = aNumber.gcd(bNumber);
         byte resBytes[] = result.toByteArray();
         for(int i = 0; i < resBytes.length; i++) {
             assertTrue(resBytes[i] == rBytes[i]);
         }
         assertEquals("incorrect sign", 0, result.signum());
     }

     /**
      * gcd: the first number is longer
      */
     public void testGcdFirstLonger() {
         byte aBytes[] = {-15, 24, 123, 56, -11, -112, -34, -98, 8, 10, 12, 14, 25, 125, -15, 28, -127};
         byte bBytes[] = {-12, 1, 0, 0, 0, 23, 44, 55, 66};
         int aSign = 1;
         int bSign = 1;
         byte rBytes[] = {7};
         BigInteger aNumber = new BigInteger(aSign, aBytes);
         BigInteger bNumber = new BigInteger(bSign, bBytes);
         BigInteger result = aNumber.gcd(bNumber);
         byte resBytes[] = new byte[rBytes.length];
         resBytes = result.toByteArray();
         for(int i = 0; i < resBytes.length; i++) {
             assertTrue(resBytes[i] == rBytes[i]);
         }
         assertEquals("incorrect sign", 1, result.signum());
     }

     /**
      * gcd: the second number is longer
      */
     public void testGcdSecondLonger() {
         byte aBytes[] = {-12, 1, 0, 0, 0, 23, 44, 55, 66};
         byte bBytes[] = {-15, 24, 123, 56, -11, -112, -34, -98, 8, 10, 12, 14, 25, 125, -15, 28, -127};
         int aSign = 1;
         int bSign = 1;
         byte rBytes[] = {7};
         BigInteger aNumber = new BigInteger(aSign, aBytes);
         BigInteger bNumber = new BigInteger(bSign, bBytes);
         BigInteger result = aNumber.gcd(bNumber);
         byte resBytes[] = new byte[rBytes.length];
         resBytes = result.toByteArray();
         for(int i = 0; i < resBytes.length; i++) {
             assertTrue(resBytes[i] == rBytes[i]);
         }
         assertEquals("incorrect sign", 1, result.signum());
     }
 }
	/*
	* 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.
	*/
	/**
	* @author Elena Semukhina
	* @version $Revision$
	*/

	package org.apache.harmony.math.tests.java.math;

	import java.math.BigInteger;

	import junit.framework.TestCase;

	/**
	* Class: java.math.BigInteger
	* Methods: modPow, modInverse, and gcd
	*/
	public class BigIntegerModPowTest extends TestCase {
	/**
	* modPow: non-positive modulus
	*/
	public void testModPowException() {
	byte aBytes[] = {1, 2, 3, 4, 5, 6, 7};
	byte eBytes[] = {1, 2, 3, 4, 5};
	byte mBytes[] = {1, 2, 3};
	int aSign = 1;
	int eSign = 1;
	int mSign = -1;
	BigInteger aNumber = new BigInteger(aSign, aBytes);
	BigInteger exp = new BigInteger(eSign, eBytes);
	BigInteger modulus = new BigInteger(mSign, mBytes);
	try {
	aNumber.modPow(exp, modulus);
	fail("ArithmeticException has not been caught");
	} catch (ArithmeticException e) {
	assertEquals("Improper exception message", "BigInteger: modulus not positive", e.getMessage());
	}
	}

	/**
	* modPow: positive exponent
	*/
	public void testModPowPosExp() {
	byte aBytes[] = {-127, 100, 56, 7, 98, -1, 39, -128, 127, 75, 48, -7};
	byte eBytes[] = {27, -15, 65, 39};
	byte mBytes[] = {-128, 2, 3, 4, 5};
	int aSign = 1;
	int eSign = 1;
	int mSign = 1;
	byte rBytes[] = {113, 100, -84, -28, -85};
	BigInteger aNumber = new BigInteger(aSign, aBytes);
	BigInteger exp = new BigInteger(eSign, eBytes);
	BigInteger modulus = new BigInteger(mSign, mBytes);
	BigInteger result = aNumber.modPow(exp, modulus);
	byte resBytes[] = new byte[rBytes.length];
	resBytes = result.toByteArray();
	for(int i = 0; i < resBytes.length; i++) {
	assertTrue(resBytes[i] == rBytes[i]);
	}
	assertEquals("incorrect sign", 1, result.signum());
	}

	/**
	* modPow: negative exponent
	*/
	public void testModPowNegExp() {
	byte aBytes[] = {-127, 100, 56, 7, 98, -1, 39, -128, 127, 75, 48, -7};
	byte eBytes[] = {27, -15, 65, 39};
	byte mBytes[] = {-128, 2, 3, 4, 5};
	int aSign = 1;
	int eSign = -1;
	int mSign = 1;
	byte rBytes[] = {12, 118, 46, 86, 92};
	BigInteger aNumber = new BigInteger(aSign, aBytes);
	BigInteger exp = new BigInteger(eSign, eBytes);
	BigInteger modulus = new BigInteger(mSign, mBytes);
	BigInteger result = aNumber.modPow(exp, modulus);
	byte resBytes[] = new byte[rBytes.length];
	resBytes = result.toByteArray();
	for(int i = 0; i < resBytes.length; i++) {
	assertTrue(resBytes[i] == rBytes[i]);
	}
	assertEquals("incorrect sign", 1, result.signum());
	}

	/**
	* modInverse: non-positive modulus
	*/
	public void testmodInverseException() {
	byte aBytes[] = {1, 2, 3, 4, 5, 6, 7};
	byte mBytes[] = {1, 2, 3};
	int aSign = 1;
	int mSign = -1;
	BigInteger aNumber = new BigInteger(aSign, aBytes);
	BigInteger modulus = new BigInteger(mSign, mBytes);
	try {
	aNumber.modInverse(modulus);
	fail("ArithmeticException has not been caught");
	} catch (ArithmeticException e) {
	assertEquals("Improper exception message", "BigInteger: modulus not positive", e.getMessage());
	}
	}

	/**
	* modInverse: non-invertible number
	*/
	public void testmodInverseNonInvertible() {
	byte aBytes[] = {-15, 24, 123, 56, -11, -112, -34, -98, 8, 10, 12, 14, 25, 125, -15, 28, -127};
	byte mBytes[] = {-12, 1, 0, 0, 0, 23, 44, 55, 66};
	int aSign = 1;
	int mSign = 1;
	BigInteger aNumber = new BigInteger(aSign, aBytes);
	BigInteger modulus = new BigInteger(mSign, mBytes);
	try {
	aNumber.modInverse(modulus);
	fail("ArithmeticException has not been caught");
	} catch (ArithmeticException e) {
	assertEquals("Improper exception message", "BigInteger not invertible.", e.getMessage());
	}
	}

	/**
	* modInverse: positive number
	*/
	public void testmodInversePos1() {
	byte aBytes[] = {24, 123, 56, -11, -112, -34, -98, 8, 10, 12, 14, 25, 125, -15, 28, -127};
	byte mBytes[] = {122, 45, 36, 100, 122, 45};
	int aSign = 1;
	int mSign = 1;
	byte rBytes[] = {47, 3, 96, 62, 87, 19};
	BigInteger aNumber = new BigInteger(aSign, aBytes);
	BigInteger modulus = new BigInteger(mSign, mBytes);
	BigInteger result = aNumber.modInverse(modulus);
	byte resBytes[] = new byte[rBytes.length];
	resBytes = result.toByteArray();
	for(int i = 0; i < resBytes.length; i++) {
	assertTrue(resBytes[i] == rBytes[i]);
	}
	assertEquals("incorrect sign", 1, result.signum());
	}

	/**
	* modInverse: positive number (another case: a < 0)
	*/
	public void testmodInversePos2() {
	byte aBytes[] = {15, 24, 123, 56, -11, -112, -34, -98, 8, 10, 12, 14, 25, 125, -15, 28, -127};
	byte mBytes[] = {2, 122, 45, 36, 100};
	int aSign = 1;
	int mSign = 1;
	byte rBytes[] = {1, -93, 40, 127, 73};
	BigInteger aNumber = new BigInteger(aSign, aBytes);
	BigInteger modulus = new BigInteger(mSign, mBytes);
	BigInteger result = aNumber.modInverse(modulus);
	byte resBytes[] = new byte[rBytes.length];
	resBytes = result.toByteArray();
	for(int i = 0; i < resBytes.length; i++) {
	assertTrue(resBytes[i] == rBytes[i]);
	}
	assertEquals("incorrect sign", 1, result.signum());
	}

	/**
	* modInverse: negative number
	*/
	public void testmodInverseNeg1() {
	byte aBytes[] = {15, 24, 123, 56, -11, -112, -34, -98, 8, 10, 12, 14, 25, 125, -15, 28, -127};
	byte mBytes[] = {2, 122, 45, 36, 100};
	int aSign = -1;
	int mSign = 1;
	byte rBytes[] = {0, -41, 4, -91, 27};
	BigInteger aNumber = new BigInteger(aSign, aBytes);
	BigInteger modulus = new BigInteger(mSign, mBytes);
	BigInteger result = aNumber.modInverse(modulus);
	byte resBytes[] = new byte[rBytes.length];
	resBytes = result.toByteArray();
	for(int i = 0; i < resBytes.length; i++) {
	assertTrue(resBytes[i] == rBytes[i]);
	}
	assertEquals("incorrect sign", 1, result.signum());
	}

	/**
	* modInverse: negative number (another case: x < 0)
	*/
	public void testmodInverseNeg2() {
	byte aBytes[] = {-15, 24, 123, 57, -15, 24, 123, 57, -15, 24, 123, 57};
	byte mBytes[] = {122, 2, 4, 122, 2, 4};
	byte rBytes[] = {85, 47, 127, 4, -128, 45};
	BigInteger aNumber = new BigInteger(aBytes);
	BigInteger modulus = new BigInteger(mBytes);
	BigInteger result = aNumber.modInverse(modulus);
	byte resBytes[] = new byte[rBytes.length];
	resBytes = result.toByteArray();
	for(int i = 0; i < resBytes.length; i++) {
	assertTrue(resBytes[i] == rBytes[i]);
	}
	assertEquals("incorrect sign", 1, result.signum());
	}

	/**
	* gcd: the second number is zero
	*/
	public void testGcdSecondZero() {
	byte aBytes[] = {15, 24, 123, 57, -15, 24, 123, 57, -15, 24, 123, 57};
	byte bBytes[] = {0};
	int aSign = 1;
	int bSign = 1;
	byte rBytes[] = {15, 24, 123, 57, -15, 24, 123, 57, -15, 24, 123, 57};
	BigInteger aNumber = new BigInteger(aSign, aBytes);
	BigInteger bNumber = new BigInteger(bSign, bBytes);
	BigInteger result = aNumber.gcd(bNumber);
	byte resBytes[] = new byte[rBytes.length];
	resBytes = result.toByteArray();
	for(int i = 0; i < resBytes.length; i++) {
	assertTrue(resBytes[i] == rBytes[i]);
	}
	assertEquals("incorrect sign", 1, result.signum());
	}

	/**
	* gcd: the first number is zero
	*/
	public void testGcdFirstZero() {
	byte aBytes[] = {0};
	byte bBytes[] = {15, 24, 123, 57, -15, 24, 123, 57, -15, 24, 123, 57};
	int aSign = 1;
	int bSign = 1;
	byte rBytes[] = {15, 24, 123, 57, -15, 24, 123, 57, -15, 24, 123, 57};
	BigInteger aNumber = new BigInteger(aSign, aBytes);
	BigInteger bNumber = new BigInteger(bSign, bBytes);
	BigInteger result = aNumber.gcd(bNumber);
	byte resBytes[] = new byte[rBytes.length];
	resBytes = result.toByteArray();
	for(int i = 0; i < resBytes.length; i++) {
	assertTrue(resBytes[i] == rBytes[i]);
	}
	assertEquals("incorrect sign", 1, result.signum());
	}

	/**
	* gcd: the first number is ZERO
	*/
	public void testGcdFirstZERO() {
	byte bBytes[] = {15, 24, 123, 57, -15, 24, 123, 57, -15, 24, 123, 57};
	int bSign = 1;
	byte rBytes[] = {15, 24, 123, 57, -15, 24, 123, 57, -15, 24, 123, 57};
	BigInteger aNumber = BigInteger.ZERO;
	BigInteger bNumber = new BigInteger(bSign, bBytes);
	BigInteger result = aNumber.gcd(bNumber);
	byte resBytes[] = new byte[rBytes.length];
	resBytes = result.toByteArray();
	for(int i = 0; i < resBytes.length; i++) {
	assertTrue(resBytes[i] == rBytes[i]);
	}
	assertEquals("incorrect sign", 1, result.signum());
	}

	/**
	* gcd: both numbers are zeros
	*/
	public void testGcdBothZeros() {
	byte rBytes[] = {0};
	BigInteger aNumber = new BigInteger("0");
	BigInteger bNumber = BigInteger.valueOf(0L);
	BigInteger result = aNumber.gcd(bNumber);
	byte resBytes[] = result.toByteArray();
	for(int i = 0; i < resBytes.length; i++) {
	assertTrue(resBytes[i] == rBytes[i]);
	}
	assertEquals("incorrect sign", 0, result.signum());
	}

	/**
	* gcd: the first number is longer
	*/
	public void testGcdFirstLonger() {
	byte aBytes[] = {-15, 24, 123, 56, -11, -112, -34, -98, 8, 10, 12, 14, 25, 125, -15, 28, -127};
	byte bBytes[] = {-12, 1, 0, 0, 0, 23, 44, 55, 66};
	int aSign = 1;
	int bSign = 1;
	byte rBytes[] = {7};
	BigInteger aNumber = new BigInteger(aSign, aBytes);
	BigInteger bNumber = new BigInteger(bSign, bBytes);
	BigInteger result = aNumber.gcd(bNumber);
	byte resBytes[] = new byte[rBytes.length];
	resBytes = result.toByteArray();
	for(int i = 0; i < resBytes.length; i++) {
	assertTrue(resBytes[i] == rBytes[i]);
	}
	assertEquals("incorrect sign", 1, result.signum());
	}

	/**
	* gcd: the second number is longer
	*/
	public void testGcdSecondLonger() {
	byte aBytes[] = {-12, 1, 0, 0, 0, 23, 44, 55, 66};
	byte bBytes[] = {-15, 24, 123, 56, -11, -112, -34, -98, 8, 10, 12, 14, 25, 125, -15, 28, -127};
	int aSign = 1;
	int bSign = 1;
	byte rBytes[] = {7};
	BigInteger aNumber = new BigInteger(aSign, aBytes);
	BigInteger bNumber = new BigInteger(bSign, bBytes);
	BigInteger result = aNumber.gcd(bNumber);
	byte resBytes[] = new byte[rBytes.length];
	resBytes = result.toByteArray();
	for(int i = 0; i < resBytes.length; i++) {
	assertTrue(resBytes[i] == rBytes[i]);
	}
	assertEquals("incorrect sign", 1, result.signum());
	}
	}