/*
    * 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_LONG_CANDIDATES;
  import static com.google.common.math.MathTesting.ALL_ROUNDING_MODES;
  import static com.google.common.math.MathTesting.ALL_SAFE_ROUNDING_MODES;
  import static com.google.common.math.MathTesting.NEGATIVE_INTEGER_CANDIDATES;
  import static com.google.common.math.MathTesting.NEGATIVE_LONG_CANDIDATES;
  import static com.google.common.math.MathTesting.POSITIVE_LONG_CANDIDATES;
  import static java.math.BigInteger.valueOf;
  import static java.math.RoundingMode.UNNECESSARY;
  
  import com.google.common.annotations.GwtCompatible;
  
  import junit.framework.TestCase;
  
  import java.math.BigDecimal;
  import java.math.BigInteger;
  import java.math.RoundingMode;
  
  /**
   * Tests for LongMath.
   *
   * @author Louis Wasserman
   */
  @GwtCompatible(emulated = true)
  public class LongMathTest extends TestCase {
    
    public void testLessThanBranchFree() {
      for (long x : ALL_LONG_CANDIDATES) {
        for (long y : ALL_LONG_CANDIDATES) {
          BigInteger difference = BigInteger.valueOf(x).subtract(BigInteger.valueOf(y));
          if (fitsInLong(difference)) {
            int expected = (x < y) ? 1 : 0;
            int actual = LongMath.lessThanBranchFree(x, y);
            assertEquals(expected, actual);
          }
        }
      }
    }
  
    // Throws an ArithmeticException if "the simple implementation" of binomial coefficients overflows
  
    public void testLog2ZeroAlwaysThrows() {
      for (RoundingMode mode : ALL_ROUNDING_MODES) {
        try {
          LongMath.log2(0L, mode);
          fail("Expected IllegalArgumentException");
        } catch (IllegalArgumentException expected) {}
      }
    }
  
    public void testLog2NegativeAlwaysThrows() {
      for (long x : NEGATIVE_LONG_CANDIDATES) {
        for (RoundingMode mode : ALL_ROUNDING_MODES) {
          try {
            LongMath.log2(x, mode);
            fail("Expected IllegalArgumentException");
          } catch (IllegalArgumentException expected) {}
        }
      }
    }
  
    /* Relies on the correctness of BigIntegerMath.log2 for all modes except UNNECESSARY. */
    public void testLog2MatchesBigInteger() {
      for (long x : POSITIVE_LONG_CANDIDATES) {
        for (RoundingMode mode : ALL_SAFE_ROUNDING_MODES) {
          // The BigInteger implementation is tested separately, use it as the reference.
          assertEquals(BigIntegerMath.log2(valueOf(x), mode), LongMath.log2(x, mode));
        }
      }
    }
  
    /* Relies on the correctness of isPowerOfTwo(long). */
    public void testLog2Exact() {
      for (long x : POSITIVE_LONG_CANDIDATES) {
        // We only expect an exception if x was not a power of 2.
        boolean isPowerOf2 = LongMath.isPowerOfTwo(x);
        try {
          assertEquals(x, 1L << LongMath.log2(x, UNNECESSARY));
          assertTrue(isPowerOf2);
        } catch (ArithmeticException e) {
          assertFalse(isPowerOf2);
        }
     }
   }
 
   // Relies on the correctness of BigIntegerMath.log10 for all modes except UNNECESSARY.
 
   // Relies on the correctness of log10(long, FLOOR) and of pow(long, int).
 
   // Relies on the correctness of BigIntegerMath.sqrt for all modes except UNNECESSARY.
 
   /* Relies on the correctness of sqrt(long, FLOOR). */
 
   public void testGCDExhaustive() {
     for (long a : POSITIVE_LONG_CANDIDATES) {
       for (long b : POSITIVE_LONG_CANDIDATES) {
         assertEquals(valueOf(a).gcd(valueOf(b)), valueOf(LongMath.gcd(a, b)));
       }
     }
   }
 
   // Depends on the correctness of BigIntegerMath.factorial.
 
   // Depends on the correctness of BigIntegerMath.binomial.
   public void testBinomial() {
     for (int n = 0; n <= 70; n++) {
       for (int k = 0; k <= n; k++) {
         BigInteger expectedBig = BigIntegerMath.binomial(n, k);
         long expectedLong = fitsInLong(expectedBig) ? expectedBig.longValue() : Long.MAX_VALUE;
         assertEquals(expectedLong, LongMath.binomial(n, k));
       }
     }
   }
 
   public void testBinomialOutside() {
     for (int n = 0; n <= 50; n++) {
       try {
         LongMath.binomial(n, -1);
         fail("Expected IllegalArgumentException");
       } catch (IllegalArgumentException expected) {}
       try {
         LongMath.binomial(n, n + 1);
         fail("Expected IllegalArgumentException");
       } catch (IllegalArgumentException expected) {}
     }
   }
 
   public void testBinomialNegative() {
     for (int n : NEGATIVE_INTEGER_CANDIDATES) {
       try {
         LongMath.binomial(n, 0);
         fail("Expected IllegalArgumentException");
       } catch (IllegalArgumentException expected) {}
     }
   }
   
   public void testSqrtOfLongIsAtMostFloorSqrtMaxLong() {
     long sqrtMaxLong = (long) Math.sqrt(Long.MAX_VALUE);
     assertTrue(sqrtMaxLong <= LongMath.FLOOR_SQRT_MAX_LONG);
   }
 
   /**
    * Helper method that asserts the arithmetic mean of x and y is equal
    * to the expectedMean.
    */
   private static void assertMean(long expectedMean, long x, long y) {
     assertEquals("The expectedMean should be the same as computeMeanSafely",
         expectedMean, computeMeanSafely(x, y));
     assertMean(x, y);
   }
 
   /**
    * Helper method that asserts the arithmetic mean of x and y is equal
    *to the result of computeMeanSafely.
    */
   private static void assertMean(long x, long y) {
     long expectedMean = computeMeanSafely(x, y);
     assertEquals(expectedMean, LongMath.mean(x, y));
     assertEquals("The mean of x and y should equal the mean of y and x",
         expectedMean, LongMath.mean(y, x));
   }
 
   /**
    * Computes the mean in a way that is obvious and resilient to
    * overflow by using BigInteger arithmetic.
    */
   private static long computeMeanSafely(long x, long y) {
     BigInteger bigX = BigInteger.valueOf(x);
     BigInteger bigY = BigInteger.valueOf(y);
     BigDecimal bigMean = new BigDecimal(bigX.add(bigY))
         .divide(BigDecimal.valueOf(2), BigDecimal.ROUND_FLOOR);
     // parseInt blows up on overflow as opposed to intValue() which does not.
     return Long.parseLong(bigMean.toString());
   }
 
   private static boolean fitsInLong(BigInteger big) {
     return big.bitLength() <= 63;
   }
 }