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  /*
   * 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.base.Preconditions.checkArgument;
 import static com.google.common.math.DoubleUtils.IMPLICIT_BIT;
 import static com.google.common.math.DoubleUtils.SIGNIFICAND_BITS;
 import static com.google.common.math.DoubleUtils.getSignificand;
 import static com.google.common.math.DoubleUtils.isFinite;
 import static com.google.common.math.DoubleUtils.isNormal;
 import static com.google.common.math.DoubleUtils.scaleNormalize;
 import static com.google.common.math.MathPreconditions.checkInRange;
 import static com.google.common.math.MathPreconditions.checkNonNegative;
 import static com.google.common.math.MathPreconditions.checkRoundingUnnecessary;
 
 
A class for arithmetic on doubles that is not covered by java.lang.Math.

Author(s):
Louis Wasserman
Since:
11.0
 
 public final class DoubleMath {
   /*
    * This method returns a value y such that rounding y DOWN (towards zero) gives the same result
    * as rounding x according to the specified mode.
    */
   static double roundIntermediate(double xRoundingMode mode) {
     if (!isFinite(x)) {
       throw new ArithmeticException("input is infinite or NaN");
     }
     switch (mode) {
       case :
         return x;
 
       case :
         return (x >= 0.0) ? x : Math.floor(x);
 
       case :
         return (x >= 0.0) ? Math.ceil(x) : x;
 
       case :
         return x;
 
       case :
         return (x >= 0.0) ? Math.ceil(x) : Math.floor(x);
 
       case :
         return Math.rint(x);
 
       case :
         if (isMathematicalInteger(x)) {
           return x;
         } else {
           return (x >= 0.0) ? x + 0.5 : x - 0.5;
         }
 
       case :
         if (isMathematicalInteger(x)) {
           return x;
         } else if (x >= 0.0) {
           double z = x + 0.5;
           return (z == x) ? x : DoubleUtils.nextDown(z); // x + 0.5 - epsilon
         } else {
           double z = x - 0.5;
           return (z == x) ? x : Math.nextUp(z); // x - 0.5 + epsilon
         }
 
       default:
         throw new AssertionError();
     }
   }

  
Returns the int value that is equal to x rounded with the specified rounding mode, if possible.

Throws:
java.lang.ArithmeticException if
  • x is infinite or NaN
  • x, after being rounded to a mathematical integer using the specified rounding mode, is either less than Integer.MIN_VALUE or greater than Integer.MAX_VALUE
  • x is not a mathematical integer and mode is java.math.RoundingMode.UNNECESSARY
  public static int roundToInt(double xRoundingMode mode) {
    double z = roundIntermediate(xmode);
    checkInRange(z >  - 1.0 & z <  + 1.0);
    return (intz;
  }
  private static final double MIN_INT_AS_DOUBLE = -0x1p31;
  private static final double MAX_INT_AS_DOUBLE = 0x1p31 - 1.0;

  
Returns the long value that is equal to x rounded with the specified rounding mode, if possible.

Throws:
java.lang.ArithmeticException if
  • x is infinite or NaN
  • x, after being rounded to a mathematical integer using the specified rounding mode, is either less than Long.MIN_VALUE or greater than Long.MAX_VALUE
  • x is not a mathematical integer and mode is java.math.RoundingMode.UNNECESSARY
  public static long roundToLong(double xRoundingMode mode) {
    double z = roundIntermediate(xmode);
    return (longz;
  }
  private static final double MIN_LONG_AS_DOUBLE = -0x1p63;
  /*
   * We cannot store Long.MAX_VALUE as a double without losing precision.  Instead, we store
   * Long.MAX_VALUE + 1 == -Long.MIN_VALUE, and then offset all comparisons by 1.
   */
  private static final double MAX_LONG_AS_DOUBLE_PLUS_ONE = 0x1p63;

  
Returns the BigInteger value that is equal to x rounded with the specified rounding mode, if possible.

Throws:
java.lang.ArithmeticException if
  public static BigInteger roundToBigInteger(double xRoundingMode mode) {
    x = roundIntermediate(xmode);
    if ( - x < 1.0 & x < ) {
      return BigInteger.valueOf((longx);
    }
    int exponent = Math.getExponent(x);
    if (exponent < 0) {
      return .;
    }
    long significand = getSignificand(x);
    BigInteger result = BigInteger.valueOf(significand).shiftLeft(exponent - );
    return (x < 0) ? result.negate() : result;
  }

  
Returns true if x is exactly equal to 2^k for some finite integer k.
  public static boolean isPowerOfTwo(double x) {
    return x > 0.0 && isFinite(x) && LongMath.isPowerOfTwo(getSignificand(x));
  }

  
Returns the base 2 logarithm of a double value.

Special cases:

  • If x is NaN or less than zero, the result is NaN.
  • If x is positive infinity, the result is positive infinity.
  • If x is positive or negative zero, the result is negative infinity.

The computed result must be within 1 ulp of the exact result.

If the result of this method will be immediately rounded to an int, log2(double,java.math.RoundingMode) is faster.

  public static double log2(double x) {
    return Math.log(x) / // surprisingly within 1 ulp according to tests
  }
  private static final double LN_2 = Math.log(2);

  
Returns the base 2 logarithm of a double value, rounded with the specified rounding mode to an int.

Regardless of the rounding mode, this is faster than (int) log2(x).

Throws:
java.lang.IllegalArgumentException if x <= 0.0, x is NaN, or x is infinite
  @SuppressWarnings("fallthrough")
  public static int log2(double xRoundingMode mode) {
    checkArgument(x > 0.0 && isFinite(x), "x must be positive and finite");
    int exponent = Math.getExponent(x);
    if (!isNormal(x)) {
      return log2(x * mode) - ;
      // Do the calculation on a normal value.
    }
    // x is positive, finite, and normal
    boolean increment;
    switch (mode) {
      case :
        // fall through
      case :
        increment = false;
        break;
      case :
        increment = !isPowerOfTwo(x);
        break;
      case :
        increment = exponent < 0 & !isPowerOfTwo(x);
        break;
      case :
        increment = exponent >= 0 & !isPowerOfTwo(x);
        break;
      case :
      case :
      case :
        double xScaled = scaleNormalize(x);
        // sqrt(2) is irrational, and the spec is relative to the "exact numerical result,"
        // so log2(x) is never exactly exponent + 0.5.
        increment = (xScaled * xScaled) > 2.0;
        break;
      default:
        throw new AssertionError();
    }
    return increment ? exponent + 1 : exponent;
  }

  
Returns true if x represents a mathematical integer.

This is equivalent to, but not necessarily implemented as, the expression !Double.isNaN(x) && !Double.isInfinite(x) && x == Math.rint(x).

  public static boolean isMathematicalInteger(double x) {
    return isFinite(x)
        && (x == 0.0 || 
            - Long.numberOfTrailingZeros(getSignificand(x)) <= Math.getExponent(x));
  }

  
Returns n!, that is, the product of the first n positive integers, 1 if n == 0, or e n!}, or java.lang.Double.POSITIVE_INFINITY if n! > Double.MAX_VALUE.

The result is within 1 ulp of the true value.

  public static double factorial(int n) {
    checkNonNegative("n"n);
    if (n > ) {
      return .;
    } else {
      // Multiplying the last (n & 0xf) values into their own accumulator gives a more accurate
      // result than multiplying by EVERY_SIXTEENTH_FACTORIAL[n >> 4] directly.
      double accum = 1.0;
      for (int i = 1 + (n & ~0xf); i <= ni++) {
        accum *= i;
      }
      return accum * [n >> 4];
    }
  }
  static final int MAX_FACTORIAL = 170;
  static final double[] EVERY_SIXTEENTH_FACTORIAL = {
      0x1.0p0,
      0x1.30777758p44,
      0x1.956ad0aae33a4p117,
      0x1.ee69a78d72cb6p202,
      0x1.fe478ee34844ap295,
      0x1.c619094edabffp394,
      0x1.3638dd7bd6347p498,
      0x1.7cac197cfe503p605,
      0x1.1e5dfc140e1e5p716,
      0x1.8ce85fadb707ep829,
      0x1.95d5f3d928edep945};
  private DoubleMath() {}
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