/*
    * Copyright (C) 2011 The Guava Authors
    *
    * 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.google.common.math;
  
  import static com.google.common.math.MathTesting.ALL_BIGINTEGER_CANDIDATES;
  import static com.google.common.math.MathTesting.ALL_ROUNDING_MODES;
  import static com.google.common.math.MathTesting.POSITIVE_BIGINTEGER_CANDIDATES;
  import static java.math.BigInteger.ONE;
  import static java.math.BigInteger.ZERO;
  import static java.math.RoundingMode.CEILING;
  import static java.math.RoundingMode.DOWN;
  import static java.math.RoundingMode.FLOOR;
  import static java.math.RoundingMode.HALF_DOWN;
  import static java.math.RoundingMode.HALF_EVEN;
  import static java.math.RoundingMode.HALF_UP;
  import static java.math.RoundingMode.UNNECESSARY;
  import static java.math.RoundingMode.UP;
  import static java.util.Arrays.asList;
  
  import com.google.common.annotations.GwtCompatible;
  
  import junit.framework.TestCase;
  
  import java.math.BigInteger;
  import java.math.RoundingMode;
  
  /**
   * Tests for BigIntegerMath.
   *
   * @author Louis Wasserman
   */
  @GwtCompatible(emulated = true)
  public class BigIntegerMathTest extends TestCase {
  
    public void testIsPowerOfTwo() {
      for (BigInteger x : ALL_BIGINTEGER_CANDIDATES) {
        // Checks for a single bit set.
        boolean expected = x.signum() > 0 & x.and(x.subtract(ONE)).equals(ZERO);
        assertEquals(expected, BigIntegerMath.isPowerOfTwo(x));
      }
    }
  
    public void testLog2ZeroAlwaysThrows() {
      for (RoundingMode mode : ALL_ROUNDING_MODES) {
        try {
          BigIntegerMath.log2(ZERO, mode);
          fail("Expected IllegalArgumentException");
        } catch (IllegalArgumentException expected) {}
      }
    }
  
    public void testLog2NegativeAlwaysThrows() {
      for (RoundingMode mode : ALL_ROUNDING_MODES) {
        try {
          BigIntegerMath.log2(BigInteger.valueOf(-1), mode);
          fail("Expected IllegalArgumentException");
        } catch (IllegalArgumentException expected) {}
      }
    }
  
    public void testLog2Floor() {
      for (BigInteger x : POSITIVE_BIGINTEGER_CANDIDATES) {
        for (RoundingMode mode : asList(FLOOR, DOWN)) {
          int result = BigIntegerMath.log2(x, mode);
          assertTrue(ZERO.setBit(result).compareTo(x) <= 0);
          assertTrue(ZERO.setBit(result + 1).compareTo(x) > 0);
        }
      }
    }
  
    public void testLog2Ceiling() {
      for (BigInteger x : POSITIVE_BIGINTEGER_CANDIDATES) {
        for (RoundingMode mode : asList(CEILING, UP)) {
          int result = BigIntegerMath.log2(x, mode);
          assertTrue(ZERO.setBit(result).compareTo(x) >= 0);
          assertTrue(result == 0 || ZERO.setBit(result - 1).compareTo(x) < 0);
        }
      }
    }
  
    // Relies on the correctness of isPowerOfTwo(BigInteger).
    public void testLog2Exact() {
      for (BigInteger x : POSITIVE_BIGINTEGER_CANDIDATES) {
        // We only expect an exception if x was not a power of 2.
        boolean isPowerOf2 = BigIntegerMath.isPowerOfTwo(x);
       try {
         assertEquals(x, ZERO.setBit(BigIntegerMath.log2(x, UNNECESSARY)));
         assertTrue(isPowerOf2);
       } catch (ArithmeticException e) {
         assertFalse(isPowerOf2);
       }
     }
   }
 
   public void testLog2HalfUp() {
     for (BigInteger x : POSITIVE_BIGINTEGER_CANDIDATES) {
       int result = BigIntegerMath.log2(x, HALF_UP);
       BigInteger x2 = x.pow(2);
       // x^2 < 2^(2 * result + 1), or else we would have rounded up
       assertTrue(ZERO.setBit(2 * result + 1).compareTo(x2) > 0);
       // x^2 >= 2^(2 * result - 1), or else we would have rounded down
       assertTrue(result == 0 || ZERO.setBit(2 * result - 1).compareTo(x2) <= 0);
     }
   }
 
   public void testLog2HalfDown() {
     for (BigInteger x : POSITIVE_BIGINTEGER_CANDIDATES) {
       int result = BigIntegerMath.log2(x, HALF_DOWN);
       BigInteger x2 = x.pow(2);
       // x^2 <= 2^(2 * result + 1), or else we would have rounded up
       assertTrue(ZERO.setBit(2 * result + 1).compareTo(x2) >= 0);
       // x^2 > 2^(2 * result - 1), or else we would have rounded down
       assertTrue(result == 0 || ZERO.setBit(2 * result - 1).compareTo(x2) < 0);
     }
   }
 
   // Relies on the correctness of log2(BigInteger, {HALF_UP,HALF_DOWN}).
   public void testLog2HalfEven() {
     for (BigInteger x : POSITIVE_BIGINTEGER_CANDIDATES) {
       int halfEven = BigIntegerMath.log2(x, HALF_EVEN);
       // Now figure out what rounding mode we should behave like (it depends if FLOOR was
       // odd/even).
       boolean floorWasEven = (BigIntegerMath.log2(x, FLOOR) & 1) == 0;
       assertEquals(BigIntegerMath.log2(x, floorWasEven ? HALF_DOWN : HALF_UP), halfEven);
     }
   }
 
   // Relies on the correctness of log10(BigInteger, FLOOR).
 
   // Relies on the correctness of log10(BigInteger, {HALF_UP,HALF_DOWN}).
 
   // Relies on the correctness of sqrt(BigInteger, FLOOR).
 
   // Relies on the correctness of sqrt(BigInteger, {HALF_UP,HALF_DOWN}).
 
   public void testFactorial() {
     BigInteger expected = BigInteger.ONE;
     for (int i = 1; i <= 200; i++) {
       expected = expected.multiply(BigInteger.valueOf(i));
       assertEquals(expected, BigIntegerMath.factorial(i));
     }
   }
 
   public void testFactorial0() {
     assertEquals(BigInteger.ONE, BigIntegerMath.factorial(0));
   }
 
   public void testFactorialNegative() {
     try {
       BigIntegerMath.factorial(-1);
       fail("Expected IllegalArgumentException");
     } catch (IllegalArgumentException expected) {}
   }
 
   public void testBinomialSmall() {
     runBinomialTest(0, 30);
   }
 
   // Depends on the correctness of BigIntegerMath.factorial
   private static void runBinomialTest(int firstN, int lastN) {
     for (int n = firstN; n <= lastN; n++) {
       for (int k = 0; k <= n; k++) {
         BigInteger expected = BigIntegerMath
             .factorial(n)
             .divide(BigIntegerMath.factorial(k))
             .divide(BigIntegerMath.factorial(n - k));
         assertEquals(expected, BigIntegerMath.binomial(n, k));
       }
     }
   }
 
   public void testBinomialOutside() {
     for (int n = 0; n <= 50; n++) {
       try {
         BigIntegerMath.binomial(n, -1);
         fail("Expected IllegalArgumentException");
       } catch (IllegalArgumentException expected) {}
       try {
         BigIntegerMath.binomial(n, n + 1);
         fail("Expected IllegalArgumentException");
       } catch (IllegalArgumentException expected) {}
     }
   }
 }