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/*
 * 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.
 */

package org.apache.commons.math.util;

import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Arrays;

import org.apache.commons.math.MathRuntimeException;

/**
 * Some useful additions to the built-in functions in {@link Math}.
 * @version $Revision: 830770 $ $Date: 2009-10-28 22:52:39 +0100 (mer., 28 oct. 2009) $
 */
public final class MathUtils {

    /** Smallest positive number such that 1 - EPSILON is not numerically equal to 1. */
    public static final double EPSILON = 0x1.0p-53;

    /** Safe minimum, such that 1 / SAFE_MIN does not overflow.
     * 
In IEEE 754 arithmetic, this is also the smallest normalized
     * number 2-1022.

     */
    public static final double SAFE_MIN = 0x1.0p-1022;

    /** 2 π. */
    public static final double TWO_PI = 2 * Math.PI;

    /** -1.0 cast as a byte. */
    private static final byte  NB = (byte)-1;

    /** -1.0 cast as a short. */
    private static final short NS = (short)-1;

    /** 1.0 cast as a byte. */
    private static final byte  PB = (byte)1;

    /** 1.0 cast as a short. */
    private static final short PS = (short)1;

    /** 0.0 cast as a byte. */
    private static final byte  ZB = (byte)0;

    /** 0.0 cast as a short. */
    private static final short ZS = (short)0;

    /** Gap between NaN and regular numbers. */
    private static final int NAN_GAP = 4 * 1024 * 1024;

    /** Offset to order signed double numbers lexicographically. */
    private static final long SGN_MASK = 0x8000000000000000L;

    /** All long-representable factorials */
    private static final long[] FACTORIALS = new long[] {
            1l,                  1l,                   2l,
            6l,                 24l,                 120l,
            720l,               5040l,               40320l,
            362880l,            3628800l,            39916800l,
            479001600l,         6227020800l,         87178291200l,
            1307674368000l,     20922789888000l,     355687428096000l,
            6402373705728000l, 121645100408832000l, 2432902008176640000l };

    /**
     * Private Constructor
     */
    private MathUtils() {
        super();
    }

    /**
     * Add two integers, checking for overflow.
     *
     * @param x an addend
     * @param y an addend
     * @return the sum x+y
     * @throws ArithmeticException if the result can not be represented as an
     *         int
     * @since 1.1
     */
    public static int addAndCheck(int x, int y) {
        long s = (long)x + (long)y;
        if (s < Integer.MIN_VALUE || s > Integer.MAX_VALUE) {
            throw new ArithmeticException("overflow: add");
        }
        return (int)s;
    }

    /**
     * Add two long integers, checking for overflow.
     *
     * @param a an addend
     * @param b an addend
     * @return the sum a+b
     * @throws ArithmeticException if the result can not be represented as an
     *         long
     * @since 1.2
     */
    public static long addAndCheck(long a, long b) {
        return addAndCheck(a, b, "overflow: add");
    }

    /**
     * Add two long integers, checking for overflow.
     *
     * @param a an addend
     * @param b an addend
     * @param msg the message to use for any thrown exception.
     * @return the sum a+b
     * @throws ArithmeticException if the result can not be represented as an
     *         long
     * @since 1.2
     */
    private static long addAndCheck(long a, long b, String msg) {
        long ret;
        if (a > b) {
            // use symmetry to reduce boundary cases
            ret = addAndCheck(b, a, msg);
        } else {
            // assert a <= b

            if (a < 0) {
                if (b < 0) {
                    // check for negative overflow
                    if (Long.MIN_VALUE - b <= a) {
                        ret = a + b;
                    } else {
                        throw new ArithmeticException(msg);
                    }
                } else {
                    // opposite sign addition is always safe
                    ret = a + b;
                }
            } else {
                // assert a >= 0
                // assert b >= 0

                // check for positive overflow
                if (a <= Long.MAX_VALUE - b) {
                    ret = a + b;
                } else {
                    throw new ArithmeticException(msg);
                }
            }
        }
        return ret;
    }

    /**
     * Returns an exact representation of the  Binomial
     * Coefficient, "n choose k", the number of
     * k-element subsets that can be selected from an
     * n-element set.
     * 

     * Preconditions:
     * 
    
     * 
  •  0 <= k <= n  (otherwise
     * IllegalArgumentException is thrown)
    • 
     * 
  •  The result is small enough to fit into a long. The
     * largest value of n for which all coefficients are
     *  < Long.MAX_VALUE is 66. If the computed value exceeds
     * Long.MAX_VALUE an ArithMeticException is
     * thrown.
    • 
     * 

     *
     * @param n the size of the set
     * @param k the size of the subsets to be counted
     * @return n choose k
     * @throws IllegalArgumentException if preconditions are not met.
     * @throws ArithmeticException if the result is too large to be represented
     *         by a long integer.
     */
    public static long binomialCoefficient(final int n, final int k) {
        checkBinomial(n, k);
        if ((n == k) || (k == 0)) {
            return 1;
        }
        if ((k == 1) || (k == n - 1)) {
            return n;
        }
        // Use symmetry for large k
        if (k > n / 2)
            return binomialCoefficient(n, n - k);

        // We use the formula
        // (n choose k) = n! / (n-k)! / k!
        // (n choose k) == ((n-k+1)*...*n) / (1*...*k)
        // which could be written
        // (n choose k) == (n-1 choose k-1) * n / k
        long result = 1;
        if (n <= 61) {
            // For n <= 61, the naive implementation cannot overflow.
            int i = n - k + 1;
            for (int j = 1; j <= k; j++) {
                result = result * i / j;
                i++;
            }
        } else if (n <= 66) {
            // For n > 61 but n <= 66, the result cannot overflow,
            // but we must take care not to overflow intermediate values.
            int i = n - k + 1;
            for (int j = 1; j <= k; j++) {
                // We know that (result * i) is divisible by j,
                // but (result * i) may overflow, so we split j:
                // Filter out the gcd, d, so j/d and i/d are integer.
                // result is divisible by (j/d) because (j/d)
                // is relative prime to (i/d) and is a divisor of
                // result * (i/d).
                final long d = gcd(i, j);
                result = (result / (j / d)) * (i / d);
                i++;
            }
        } else {
            // For n > 66, a result overflow might occur, so we check
            // the multiplication, taking care to not overflow
            // unnecessary.
            int i = n - k + 1;
            for (int j = 1; j <= k; j++) {
                final long d = gcd(i, j);
                result = mulAndCheck(result / (j / d), i / d);
                i++;
            }
        }
        return result;
    }

    /**
     * Returns a double representation of the  Binomial
     * Coefficient, "n choose k", the number of
     * k-element subsets that can be selected from an
     * n-element set.
     * 

     * Preconditions:
     * 
    
     * 
  •  0 <= k <= n  (otherwise
     * IllegalArgumentException is thrown)
    • 
     * 
  •  The result is small enough to fit into a double. The
     * largest value of n for which all coefficients are <
     * Double.MAX_VALUE is 1029. If the computed value exceeds Double.MAX_VALUE,
     * Double.POSITIVE_INFINITY is returned
    • 
     * 

     *
     * @param n the size of the set
     * @param k the size of the subsets to be counted
     * @return n choose k
     * @throws IllegalArgumentException if preconditions are not met.
     */
    public static double binomialCoefficientDouble(final int n, final int k) {
        checkBinomial(n, k);
        if ((n == k) || (k == 0)) {
            return 1d;
        }
        if ((k == 1) || (k == n - 1)) {
            return n;
        }
        if (k > n/2) {
            return binomialCoefficientDouble(n, n - k);
        }
        if (n < 67) {
            return binomialCoefficient(n,k);
        }

        double result = 1d;
        for (int i = 1; i <= k; i++) {
            result *= (double)(n - k + i) / (double)i;
        }

        return Math.floor(result + 0.5);
    }

    /**
     * Returns the natural log of the  Binomial
     * Coefficient, "n choose k", the number of
     * k-element subsets that can be selected from an
     * n-element set.
     * 

     * Preconditions:
     * 
    
     * 
  •  0 <= k <= n  (otherwise
     * IllegalArgumentException is thrown)
    • 
     * 

     *
     * @param n the size of the set
     * @param k the size of the subsets to be counted
     * @return n choose k
     * @throws IllegalArgumentException if preconditions are not met.
     */
    public static double binomialCoefficientLog(final int n, final int k) {
        checkBinomial(n, k);
        if ((n == k) || (k == 0)) {
            return 0;
        }
        if ((k == 1) || (k == n - 1)) {
            return Math.log(n);
        }

        /*
         * For values small enough to do exact integer computation,
         * return the log of the exact value
         */
        if (n < 67) {
            return Math.log(binomialCoefficient(n,k));
        }

        /*
         * Return the log of binomialCoefficientDouble for values that will not
         * overflow binomialCoefficientDouble
         */
        if (n < 1030) {
            return Math.log(binomialCoefficientDouble(n, k));
        }

        if (k > n / 2) {
            return binomialCoefficientLog(n, n - k);
        }

        /*
         * Sum logs for values that could overflow
         */
        double logSum = 0;

        // n!/(n-k)!
        for (int i = n - k + 1; i <= n; i++) {
            logSum += Math.log(i);
        }

        // divide by k!
        for (int i = 2; i <= k; i++) {
            logSum -= Math.log(i);
        }

        return logSum;
    }

    /**
     * Check binomial preconditions.
     * @param n the size of the set
     * @param k the size of the subsets to be counted
     * @exception IllegalArgumentException if preconditions are not met.
     */
    private static void checkBinomial(final int n, final int k)
            throws IllegalArgumentException {
        if (n < k) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "must have n >= k for binomial coefficient (n,k), got n = {0}, k = {1}",
                    n, k);
        }
        if (n < 0) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "must have n >= 0 for binomial coefficient (n,k), got n = {0}",
                    n);
        }
    }

    /**
     * Compares two numbers given some amount of allowed error.
     *
     * @param x the first number
     * @param y the second number
     * @param eps the amount of error to allow when checking for equality
     * @return 
  • 0 if  {@link #equals(double, double, double) equals(x, y, eps)}
    • 
     *       
  • < 0 if !{@link #equals(double, double, double) equals(x, y, eps)} && x < y
    • 
     *       
  • > 0 if !{@link #equals(double, double, double) equals(x, y, eps)} && x > y

     */
    public static int compareTo(double x, double y, double eps) {
        if (equals(x, y, eps)) {
            return 0;
        } else if (x < y) {
            return -1;
        }
        return 1;
    }

    /**
     * Returns the 
     * hyperbolic cosine of x.
     *
     * @param x double value for which to find the hyperbolic cosine
     * @return hyperbolic cosine of x
     */
    public static double cosh(double x) {
        return (Math.exp(x) + Math.exp(-x)) / 2.0;
    }

    /**
     * Returns true iff both arguments are NaN or neither is NaN and they are
     * equal
     *
     * @param x first value
     * @param y second value
     * @return true if the values are equal or both are NaN
     */
    public static boolean equals(double x, double y) {
        return (Double.isNaN(x) && Double.isNaN(y)) || x == y;
    }

    /**
     * Returns true iff both arguments are equal or within the range of allowed
     * error (inclusive).
     * 

     * Two NaNs are considered equals, as are two infinities with same sign.
     * 

     *
     * @param x first value
     * @param y second value
     * @param eps the amount of absolute error to allow
     * @return true if the values are equal or within range of each other
     */
    public static boolean equals(double x, double y, double eps) {
        return equals(x, y) || (Math.abs(y - x) <= eps);
    }

    /**
     * Returns true iff both arguments are equal or within the range of allowed
     * error (inclusive).
     * Adapted from 
     * Bruce Dawson
     *
     * @param x first value
     * @param y second value
     * @param maxUlps {@code (maxUlps - 1)} is the number of floating point
     * values between {@code x} and {@code y}.
     * @return {@code true} if there are less than {@code maxUlps} floating
     * point values between {@code x} and {@code y}
     */
    public static boolean equals(double x, double y, int maxUlps) {
        // Check that "maxUlps" is non-negative and small enough so that the
        // default NAN won't compare as equal to anything.
        assert maxUlps > 0 && maxUlps < NAN_GAP;

        long xInt = Double.doubleToLongBits(x);
        long yInt = Double.doubleToLongBits(y);

        // Make lexicographically ordered as a two's-complement integer.
        if (xInt < 0) {
            xInt = SGN_MASK - xInt;
        }
        if (yInt < 0) {
            yInt = SGN_MASK - yInt;
        }

        return Math.abs(xInt - yInt) <= maxUlps;
    }

    /**
     * Returns true iff both arguments are null or have same dimensions
     * and all their elements are {@link #equals(double,double) equals}
     *
     * @param x first array
     * @param y second array
     * @return true if the values are both null or have same dimension
     * and equal elements
     * @since 1.2
     */
    public static boolean equals(double[] x, double[] y) {
        if ((x == null) || (y == null)) {
            return !((x == null) ^ (y == null));
        }
        if (x.length != y.length) {
            return false;
        }
        for (int i = 0; i < x.length; ++i) {
            if (!equals(x[i], y[i])) {
                return false;
            }
        }
        return true;
    }

    /**
     * Returns n!. Shorthand for n  Factorial, the
     * product of the numbers 1,...,n.
     * 

     * Preconditions:
     * 
    
     * 
  •  n >= 0 (otherwise
     * IllegalArgumentException is thrown)
    • 
     * 
  •  The result is small enough to fit into a long. The
     * largest value of n for which n! <
     * Long.MAX_VALUE is 20. If the computed value exceeds Long.MAX_VALUE
     * an ArithMeticException  is thrown.
    • 
     * 

     * 

     *
     * @param n argument
     * @return n!
     * @throws ArithmeticException if the result is too large to be represented
     *         by a long integer.
     * @throws IllegalArgumentException if n < 0
     */
    public static long factorial(final int n) {
        if (n < 0) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "must have n >= 0 for n!, got n = {0}",
                    n);
        }
        if (n > 20) {
            throw new ArithmeticException(
                    "factorial value is too large to fit in a long");
        }
        return FACTORIALS[n];
    }

    /**
     * Returns n!. Shorthand for n  Factorial, the
     * product of the numbers 1,...,n as a double.
     * 

     * Preconditions:
     * 
    
     * 
  •  n >= 0 (otherwise
     * IllegalArgumentException is thrown)
    • 
     * 
  •  The result is small enough to fit into a double. The
     * largest value of n for which n! <
     * Double.MAX_VALUE is 170. If the computed value exceeds
     * Double.MAX_VALUE, Double.POSITIVE_INFINITY is returned
    • 
     * 

     * 

     *
     * @param n argument
     * @return n!
     * @throws IllegalArgumentException if n < 0
     */
    public static double factorialDouble(final int n) {
        if (n < 0) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "must have n >= 0 for n!, got n = {0}",
                    n);
        }
        if (n < 21) {
            return factorial(n);
        }
        return Math.floor(Math.exp(factorialLog(n)) + 0.5);
    }

    /**
     * Returns the natural logarithm of n!.
     * 

     * Preconditions:
     * 
    
     * 
  •  n >= 0 (otherwise
     * IllegalArgumentException is thrown)
    • 
     * 

     *
     * @param n argument
     * @return n!
     * @throws IllegalArgumentException if preconditions are not met.
     */
    public static double factorialLog(final int n) {
        if (n < 0) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "must have n >= 0 for n!, got n = {0}",
                    n);
        }
        if (n < 21) {
            return Math.log(factorial(n));
        }
        double logSum = 0;
        for (int i = 2; i <= n; i++) {
            logSum += Math.log(i);
        }
        return logSum;
    }

    /**
     * 

     * Gets the greatest common divisor of the absolute value of two numbers,
     * using the "binary gcd" method which avoids division and modulo
     * operations. See Knuth 4.5.2 algorithm B. This algorithm is due to Josef
     * Stein (1961).
     * 

     * Special cases:
     * 
    
     * 
  • The invocations
     * gcd(Integer.MIN_VALUE, Integer.MIN_VALUE),
     * gcd(Integer.MIN_VALUE, 0) and
     * gcd(0, Integer.MIN_VALUE) throw an
     * ArithmeticException, because the result would be 2^31, which
     * is too large for an int value.
    • 
     * 
  • The result of gcd(x, x), gcd(0, x) and
     * gcd(x, 0) is the absolute value of x, except
     * for the special cases above.
     * 
  • The invocation gcd(0, 0) is the only one which returns
     * 0.
    • 
     * 

     *
     * @param p any number
     * @param q any number
     * @return the greatest common divisor, never negative
     * @throws ArithmeticException
     *             if the result cannot be represented as a nonnegative int
     *             value
     * @since 1.1
     */
    public static int gcd(final int p, final int q) {
        int u = p;
        int v = q;
        if ((u == 0) || (v == 0)) {
            if ((u == Integer.MIN_VALUE) || (v == Integer.MIN_VALUE)) {
                throw MathRuntimeException.createArithmeticException(
                        "overflow: gcd({0}, {1}) is 2^31",
                        p, q);
            }
            return Math.abs(u) + Math.abs(v);
        }
        // keep u and v negative, as negative integers range down to
        // -2^31, while positive numbers can only be as large as 2^31-1
        // (i.e. we can't necessarily negate a negative number without
        // overflow)
        /* assert u!=0 && v!=0; */
        if (u > 0) {
            u = -u;
        } // make u negative
        if (v > 0) {
            v = -v;
        } // make v negative
        // B1. [Find power of 2]
        int k = 0;
        while ((u & 1) == 0 && (v & 1) == 0 && k < 31) { // while u and v are
            // both even...
            u /= 2;
            v /= 2;
            k++; // cast out twos.
        }
        if (k == 31) {
            throw MathRuntimeException.createArithmeticException(
                    "overflow: gcd({0}, {1}) is 2^31",
                    p, q);
        }
        // B2. Initialize: u and v have been divided by 2^k and at least
        // one is odd.
        int t = ((u & 1) == 1) ? v : -(u / 2)/* B3 */;
        // t negative: u was odd, v may be even (t replaces v)
        // t positive: u was even, v is odd (t replaces u)
        do {
            /* assert u<0 && v<0; */
            // B4/B3: cast out twos from t.
            while ((t & 1) == 0) { // while t is even..
                t /= 2; // cast out twos
            }
            // B5 [reset max(u,v)]
            if (t > 0) {
                u = -t;
            } else {
                v = t;
            }
            // B6/B3. at this point both u and v should be odd.
            t = (v - u) / 2;
            // |u| larger: t positive (replace u)
            // |v| larger: t negative (replace v)
        } while (t != 0);
        return -u * (1 << k); // gcd is u*2^k
    }

    /**
     * Returns an integer hash code representing the given double value.
     *
     * @param value the value to be hashed
     * @return the hash code
     */
    public static int hash(double value) {
        return new Double(value).hashCode();
    }

    /**
     * Returns an integer hash code representing the given double array.
     *
     * @param value the value to be hashed (may be null)
     * @return the hash code
     * @since 1.2
     */
    public static int hash(double[] value) {
        return Arrays.hashCode(value);
    }

    /**
     * For a byte value x, this method returns (byte)(+1) if x >= 0 and
     * (byte)(-1) if x < 0.
     *
     * @param x the value, a byte
     * @return (byte)(+1) or (byte)(-1), depending on the sign of x
     */
    public static byte indicator(final byte x) {
        return (x >= ZB) ? PB : NB;
    }

    /**
     * For a double precision value x, this method returns +1.0 if x >= 0 and
     * -1.0 if x < 0. Returns NaN if x is
     * NaN.
     *
     * @param x the value, a double
     * @return +1.0 or -1.0, depending on the sign of x
     */
    public static double indicator(final double x) {
        if (Double.isNaN(x)) {
            return Double.NaN;
        }
        return (x >= 0.0) ? 1.0 : -1.0;
    }

    /**
     * For a float value x, this method returns +1.0F if x >= 0 and -1.0F if x <
     * 0. Returns NaN if x is NaN.
     *
     * @param x the value, a float
     * @return +1.0F or -1.0F, depending on the sign of x
     */
    public static float indicator(final float x) {
        if (Float.isNaN(x)) {
            return Float.NaN;
        }
        return (x >= 0.0F) ? 1.0F : -1.0F;
    }

    /**
     * For an int value x, this method returns +1 if x >= 0 and -1 if x < 0.
     *
     * @param x the value, an int
     * @return +1 or -1, depending on the sign of x
     */
    public static int indicator(final int x) {
        return (x >= 0) ? 1 : -1;
    }

    /**
     * For a long value x, this method returns +1L if x >= 0 and -1L if x < 0.
     *
     * @param x the value, a long
     * @return +1L or -1L, depending on the sign of x
     */
    public static long indicator(final long x) {
        return (x >= 0L) ? 1L : -1L;
    }

    /**
     * For a short value x, this method returns (short)(+1) if x >= 0 and
     * (short)(-1) if x < 0.
     *
     * @param x the value, a short
     * @return (short)(+1) or (short)(-1), depending on the sign of x
     */
    public static short indicator(final short x) {
        return (x >= ZS) ? PS : NS;
    }

    /**
     * 

     * Returns the least common multiple of the absolute value of two numbers,
     * using the formula lcm(a,b) = (a / gcd(a,b)) * b.
     * 

     * Special cases:
     * 
    
     * 
  • The invocations lcm(Integer.MIN_VALUE, n) and
     * lcm(n, Integer.MIN_VALUE), where abs(n) is a
     * power of 2, throw an ArithmeticException, because the result
     * would be 2^31, which is too large for an int value.
    • 
     * 
  • The result of lcm(0, x) and lcm(x, 0) is
     * 0 for any x.
     * 

     *
     * @param a any number
     * @param b any number
     * @return the least common multiple, never negative
     * @throws ArithmeticException
     *             if the result cannot be represented as a nonnegative int
     *             value
     * @since 1.1
     */
    public static int lcm(int a, int b) {
        if (a==0 || b==0){
            return 0;
        }
        int lcm = Math.abs(mulAndCheck(a / gcd(a, b), b));
        if (lcm == Integer.MIN_VALUE){
            throw new ArithmeticException("overflow: lcm is 2^31");
        }
        return lcm;
    }

    /**
     * 
Returns the
     * logarithm
     * for base b of x.
     * 

     * 
Returns NaN if either argument is negative.  If
     * base is 0 and x is positive, 0 is returned.
     * If base is positive and x is 0,
     * Double.NEGATIVE_INFINITY is returned.  If both arguments
     * are 0, the result is NaN.

     *
     * @param base the base of the logarithm, must be greater than 0
     * @param x argument, must be greater than 0
     * @return the value of the logarithm - the number y such that base^y = x.
     * @since 1.2
     */
    public static double log(double base, double x) {
        return Math.log(x)/Math.log(base);
    }

    /**
     * Multiply two integers, checking for overflow.
     *
     * @param x a factor
     * @param y a factor
     * @return the product x*y
     * @throws ArithmeticException if the result can not be represented as an
     *         int
     * @since 1.1
     */
    public static int mulAndCheck(int x, int y) {
        long m = ((long)x) * ((long)y);
        if (m < Integer.MIN_VALUE || m > Integer.MAX_VALUE) {
            throw new ArithmeticException("overflow: mul");
        }
        return (int)m;
    }

    /**
     * Multiply two long integers, checking for overflow.
     *
     * @param a first value
     * @param b second value
     * @return the product a * b
     * @throws ArithmeticException if the result can not be represented as an
     *         long
     * @since 1.2
     */
    public static long mulAndCheck(long a, long b) {
        long ret;
        String msg = "overflow: multiply";
        if (a > b) {
            // use symmetry to reduce boundary cases
            ret = mulAndCheck(b, a);
        } else {
            if (a < 0) {
                if (b < 0) {
                    // check for positive overflow with negative a, negative b
                    if (a >= Long.MAX_VALUE / b) {
                        ret = a * b;
                    } else {
                        throw new ArithmeticException(msg);
                    }
                } else if (b > 0) {
                    // check for negative overflow with negative a, positive b
                    if (Long.MIN_VALUE / b <= a) {
                        ret = a * b;
                    } else {
                        throw new ArithmeticException(msg);

                    }
                } else {
                    // assert b == 0
                    ret = 0;
                }
            } else if (a > 0) {
                // assert a > 0
                // assert b > 0

                // check for positive overflow with positive a, positive b
                if (a <= Long.MAX_VALUE / b) {
                    ret = a * b;
                } else {
                    throw new ArithmeticException(msg);
                }
            } else {
                // assert a == 0
                ret = 0;
            }
        }
        return ret;
    }

    /**
     * Get the next machine representable number after a number, moving
     * in the direction of another number.
     * 

     * If direction is greater than or equal tod,
     * the smallest machine representable number strictly greater than
     * d is returned; otherwise the largest representable number
     * strictly less than d is returned.

     * 

     * If d is NaN or Infinite, it is returned unchanged.

     *
     * @param d base number
     * @param direction (the only important thing is whether
     * direction is greater or smaller than d)
     * @return the next machine representable number in the specified direction
     * @since 1.2
     */
    public static double nextAfter(double d, double direction) {

        // handling of some important special cases
        if (Double.isNaN(d) || Double.isInfinite(d)) {
            return d;
        } else if (d == 0) {
            return (direction < 0) ? -Double.MIN_VALUE : Double.MIN_VALUE;
        }
        // special cases MAX_VALUE to infinity and  MIN_VALUE to 0
        // are handled just as normal numbers

        // split the double in raw components
        long bits     = Double.doubleToLongBits(d);
        long sign     = bits & 0x8000000000000000L;
        long exponent = bits & 0x7ff0000000000000L;
        long mantissa = bits & 0x000fffffffffffffL;

        if (d * (direction - d) >= 0) {
            // we should increase the mantissa
            if (mantissa == 0x000fffffffffffffL) {
                return Double.longBitsToDouble(sign |
                        (exponent + 0x0010000000000000L));
            } else {
                return Double.longBitsToDouble(sign |
                        exponent | (mantissa + 1));
            }
        } else {
            // we should decrease the mantissa
            if (mantissa == 0L) {
                return Double.longBitsToDouble(sign |
                        (exponent - 0x0010000000000000L) |
                        0x000fffffffffffffL);
            } else {
                return Double.longBitsToDouble(sign |
                        exponent | (mantissa - 1));
            }
        }

    }

    /**
     * Scale a number by 2scaleFactor.
     * 
If d is 0 or NaN or Infinite, it is returned unchanged.

     *
     * @param d base number
     * @param scaleFactor power of two by which d sould be multiplied
     * @return d × 2scaleFactor
     * @since 2.0
     */
    public static double scalb(final double d, final int scaleFactor) {

        // handling of some important special cases
        if ((d == 0) || Double.isNaN(d) || Double.isInfinite(d)) {
            return d;
        }

        // split the double in raw components
        final long bits     = Double.doubleToLongBits(d);
        final long exponent = bits & 0x7ff0000000000000L;
        final long rest     = bits & 0x800fffffffffffffL;

        // shift the exponent
        final long newBits = rest | (exponent + (((long) scaleFactor) << 52));
        return Double.longBitsToDouble(newBits);

    }

    /**
     * Normalize an angle in a 2&pi wide interval around a center value.
     * 
This method has three main uses:

     * 
    
     *   
  • normalize an angle between 0 and 2π:
    
     *       a = MathUtils.normalizeAngle(a, Math.PI);
    • 
     *   
  • normalize an angle between -π and +π
    
     *       a = MathUtils.normalizeAngle(a, 0.0);
    • 
     *   
  • compute the angle between two defining angular positions:
    
     *       angle = MathUtils.normalizeAngle(end, start) - start;
    • 
     * 

     * 
Note that due to numerical accuracy and since π cannot be represented
     * exactly, the result interval is closed, it cannot be half-closed
     * as would be more satisfactory in a purely mathematical view.

     * @param a angle to normalize
     * @param center center of the desired 2π interval for the result
     * @return a-2kπ with integer k and center-π <= a-2kπ <= center+π
     * @since 1.2
     */
    public static double normalizeAngle(double a, double center) {
        return a - TWO_PI * Math.floor((a + Math.PI - center) / TWO_PI);
    }

    /**
     * 
Normalizes an array to make it sum to a specified value.
     * Returns the result of the transformation 
     *    x |-> x * normalizedSum / sum
     * 

     * applied to each non-NaN element x of the input array, where sum is the
     * sum of the non-NaN entries in the input array.

     *
     * 
Throws IllegalArgumentException if normalizedSum is infinite
     * or NaN and ArithmeticException if the input array contains any infinite elements
     * or sums to 0

     *
     * 
Ignores (i.e., copies unchanged to the output array) NaNs in the input array.

     *
     * @param values input array to be normalized
     * @param normalizedSum target sum for the normalized array
     * @return normalized array
     * @throws ArithmeticException if the input array contains infinite elements or sums to zero
     * @throws IllegalArgumentException if the target sum is infinite or NaN
     */
    public static double[] normalizeArray(double[] values, double normalizedSum)
            throws ArithmeticException, IllegalArgumentException {
        if (Double.isInfinite(normalizedSum)) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "Cannot normalize to an infinite value");
        }
        if (Double.isNaN(normalizedSum)) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "Cannot normalize to NaN");
        }
        double sum = 0d;
        final int len = values.length;
        double[] out = new double[len];
        for (int i = 0; i < len; i++) {
            if (Double.isInfinite(values[i])) {
                throw MathRuntimeException.createArithmeticException(
                        "Array contains an infinite element, {0} at index {1}", values[i], i);
            }
            if (!Double.isNaN(values[i])) {
                sum += values[i];
            }
        }
        if (sum == 0) {
            throw MathRuntimeException.createArithmeticException(
                    "Array sums to zero");
        }
        for (int i = 0; i < len; i++) {
            if (Double.isNaN(values[i])) {
                out[i] = Double.NaN;
            } else {
                out[i] = values[i] * normalizedSum / sum;
            }
        }
        return out;
    }

    /**
     * Round the given value to the specified number of decimal places. The
     * value is rounded using the {@link BigDecimal#ROUND_HALF_UP} method.
     *
     * @param x the value to round.
     * @param scale the number of digits to the right of the decimal point.
     * @return the rounded value.
     * @since 1.1
     */
    public static double round(double x, int scale) {
        return round(x, scale, BigDecimal.ROUND_HALF_UP);
    }

    /**
     * Round the given value to the specified number of decimal places. The
     * value is rounded using the given method which is any method defined in
     * {@link BigDecimal}.
     *
     * @param x the value to round.
     * @param scale the number of digits to the right of the decimal point.
     * @param roundingMethod the rounding method as defined in
     *        {@link BigDecimal}.
     * @return the rounded value.
     * @since 1.1
     */
    public static double round(double x, int scale, int roundingMethod) {
        try {
            return (new BigDecimal
                    (Double.toString(x))
                    .setScale(scale, roundingMethod))
                    .doubleValue();
        } catch (NumberFormatException ex) {
            if (Double.isInfinite(x)) {
                return x;
            } else {
                return Double.NaN;
            }
        }
    }

    /**
     * Round the given value to the specified number of decimal places. The
     * value is rounding using the {@link BigDecimal#ROUND_HALF_UP} method.
     *
     * @param x the value to round.
     * @param scale the number of digits to the right of the decimal point.
     * @return the rounded value.
     * @since 1.1
     */
    public static float round(float x, int scale) {
        return round(x, scale, BigDecimal.ROUND_HALF_UP);
    }

    /**
     * Round the given value to the specified number of decimal places. The
     * value is rounded using the given method which is any method defined in
     * {@link BigDecimal}.
     *
     * @param x the value to round.
     * @param scale the number of digits to the right of the decimal point.
     * @param roundingMethod the rounding method as defined in
     *        {@link BigDecimal}.
     * @return the rounded value.
     * @since 1.1
     */
    public static float round(float x, int scale, int roundingMethod) {
        float sign = indicator(x);
        float factor = (float)Math.pow(10.0f, scale) * sign;
        return (float)roundUnscaled(x * factor, sign, roundingMethod) / factor;
    }

    /**
     * Round the given non-negative, value to the "nearest" integer. Nearest is
     * determined by the rounding method specified. Rounding methods are defined
     * in {@link BigDecimal}.
     *
     * @param unscaled the value to round.
     * @param sign the sign of the original, scaled value.
     * @param roundingMethod the rounding method as defined in
     *        {@link BigDecimal}.
     * @return the rounded value.
     * @since 1.1
     */
    private static double roundUnscaled(double unscaled, double sign,
                                        int roundingMethod) {
        switch (roundingMethod) {
            case BigDecimal.ROUND_CEILING :
                if (sign == -1) {
                    unscaled = Math.floor(nextAfter(unscaled, Double.NEGATIVE_INFINITY));
                } else {
                    unscaled = Math.ceil(nextAfter(unscaled, Double.POSITIVE_INFINITY));
                }
                break;
            case BigDecimal.ROUND_DOWN :
                unscaled = Math.floor(nextAfter(unscaled, Double.NEGATIVE_INFINITY));
                break;
            case BigDecimal.ROUND_FLOOR :
                if (sign == -1) {
                    unscaled = Math.ceil(nextAfter(unscaled, Double.POSITIVE_INFINITY));
                } else {
                    unscaled = Math.floor(nextAfter(unscaled, Double.NEGATIVE_INFINITY));
                }
                break;
            case BigDecimal.ROUND_HALF_DOWN : {
                unscaled = nextAfter(unscaled, Double.NEGATIVE_INFINITY);
                double fraction = unscaled - Math.floor(unscaled);
                if (fraction > 0.5) {
                    unscaled = Math.ceil(unscaled);
                } else {
                    unscaled = Math.floor(unscaled);
                }
                break;
            }
            case BigDecimal.ROUND_HALF_EVEN : {
                double fraction = unscaled - Math.floor(unscaled);
                if (fraction > 0.5) {
                    unscaled = Math.ceil(unscaled);
                } else if (fraction < 0.5) {
                    unscaled = Math.floor(unscaled);
                } else {
                    // The following equality test is intentional and needed for rounding purposes
                    if (Math.floor(unscaled) / 2.0 == Math.floor(Math
                            .floor(unscaled) / 2.0)) { // even
                        unscaled = Math.floor(unscaled);
                    } else { // odd
                        unscaled = Math.ceil(unscaled);
                    }
                }
                break;
            }
            case BigDecimal.ROUND_HALF_UP : {
                unscaled = nextAfter(unscaled, Double.POSITIVE_INFINITY);
                double fraction = unscaled - Math.floor(unscaled);
                if (fraction >= 0.5) {
                    unscaled = Math.ceil(unscaled);
                } else {
                    unscaled = Math.floor(unscaled);
                }
                break;
            }
            case BigDecimal.ROUND_UNNECESSARY :
                if (unscaled != Math.floor(unscaled)) {
                    throw new ArithmeticException("Inexact result from rounding");
                }
                break;
            case BigDecimal.ROUND_UP :
                unscaled = Math.ceil(nextAfter(unscaled,  Double.POSITIVE_INFINITY));
                break;
            default :
                throw MathRuntimeException.createIllegalArgumentException(
                        "invalid rounding method {0}, valid methods: {1} ({2}), {3} ({4})," +
                                " {5} ({6}), {7} ({8}), {9} ({10}), {11} ({12}), {13} ({14}), {15} ({16})",
                        roundingMethod,
                        "ROUND_CEILING",     BigDecimal.ROUND_CEILING,
                        "ROUND_DOWN",        BigDecimal.ROUND_DOWN,
                        "ROUND_FLOOR",       BigDecimal.ROUND_FLOOR,
                        "ROUND_HALF_DOWN",   BigDecimal.ROUND_HALF_DOWN,
                        "ROUND_HALF_EVEN",   BigDecimal.ROUND_HALF_EVEN,
                        "ROUND_HALF_UP",     BigDecimal.ROUND_HALF_UP,
                        "ROUND_UNNECESSARY", BigDecimal.ROUND_UNNECESSARY,
                        "ROUND_UP",          BigDecimal.ROUND_UP);
        }
        return unscaled;
    }

    /**
     * Returns the  sign
     * for byte value x.
     * 

     * For a byte value x, this method returns (byte)(+1) if x > 0, (byte)(0) if
     * x = 0, and (byte)(-1) if x < 0.

     *
     * @param x the value, a byte
     * @return (byte)(+1), (byte)(0), or (byte)(-1), depending on the sign of x
     */
    public static byte sign(final byte x) {
        return (x == ZB) ? ZB : (x > ZB) ? PB : NB;
    }

    /**
     * Returns the  sign
     * for double precision x.
     * 

     * For a double value x, this method returns
     * +1.0 if x > 0, 0.0 if
     * x = 0.0, and -1.0 if x < 0.
     * Returns NaN if x is NaN.

     *
     * @param x the value, a double
     * @return +1.0, 0.0, or -1.0, depending on the sign of x
     */
    public static double sign(final double x) {
        if (Double.isNaN(x)) {
            return Double.NaN;
        }
        return (x == 0.0) ? 0.0 : (x > 0.0) ? 1.0 : -1.0;
    }

    /**
     * Returns the  sign
     * for float value x.
     * 

     * For a float value x, this method returns +1.0F if x > 0, 0.0F if x =
     * 0.0F, and -1.0F if x < 0. Returns NaN if x
     * is NaN.

     *
     * @param x the value, a float
     * @return +1.0F, 0.0F, or -1.0F, depending on the sign of x
     */
    public static float sign(final float x) {
        if (Float.isNaN(x)) {
            return Float.NaN;
        }
        return (x == 0.0F) ? 0.0F : (x > 0.0F) ? 1.0F : -1.0F;
    }

    /**
     * Returns the  sign
     * for int value x.
     * 

     * For an int value x, this method returns +1 if x > 0, 0 if x = 0, and -1
     * if x < 0.

     *
     * @param x the value, an int
     * @return +1, 0, or -1, depending on the sign of x
     */
    public static int sign(final int x) {
        return (x == 0) ? 0 : (x > 0) ? 1 : -1;
    }

    /**
     * Returns the  sign
     * for long value x.
     * 

     * For a long value x, this method returns +1L if x > 0, 0L if x = 0, and
     * -1L if x < 0.

     *
     * @param x the value, a long
     * @return +1L, 0L, or -1L, depending on the sign of x
     */
    public static long sign(final long x) {
        return (x == 0L) ? 0L : (x > 0L) ? 1L : -1L;
    }

    /**
     * Returns the  sign
     * for short value x.
     * 

     * For a short value x, this method returns (short)(+1) if x > 0, (short)(0)
     * if x = 0, and (short)(-1) if x < 0.

     *
     * @param x the value, a short
     * @return (short)(+1), (short)(0), or (short)(-1), depending on the sign of
     *         x
     */
    public static short sign(final short x) {
        return (x == ZS) ? ZS : (x > ZS) ? PS : NS;
    }

    /**
     * Returns the 
     * hyperbolic sine of x.
     *
     * @param x double value for which to find the hyperbolic sine
     * @return hyperbolic sine of x
     */
    public static double sinh(double x) {
        return (Math.exp(x) - Math.exp(-x)) / 2.0;
    }

    /**
     * Subtract two integers, checking for overflow.
     *
     * @param x the minuend
     * @param y the subtrahend
     * @return the difference x-y
     * @throws ArithmeticException if the result can not be represented as an
     *         int
     * @since 1.1
     */
    public static int subAndCheck(int x, int y) {
        long s = (long)x - (long)y;
        if (s < Integer.MIN_VALUE || s > Integer.MAX_VALUE) {
            throw new ArithmeticException("overflow: subtract");
        }
        return (int)s;
    }

    /**
     * Subtract two long integers, checking for overflow.
     *
     * @param a first value
     * @param b second value
     * @return the difference a-b
     * @throws ArithmeticException if the result can not be represented as an
     *         long
     * @since 1.2
     */
    public static long subAndCheck(long a, long b) {
        long ret;
        String msg = "overflow: subtract";
        if (b == Long.MIN_VALUE) {
            if (a < 0) {
                ret = a - b;
            } else {
                throw new ArithmeticException(msg);
            }
        } else {
            // use additive inverse
            ret = addAndCheck(a, -b, msg);
        }
        return ret;
    }

    /**
     * Raise an int to an int power.
     * @param k number to raise
     * @param e exponent (must be positive or null)
     * @return ke
     * @exception IllegalArgumentException if e is negative
     */
    public static int pow(final int k, int e)
            throws IllegalArgumentException {

        if (e < 0) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "cannot raise an integral value to a negative power ({0}^{1})",
                    k, e);
        }

        int result = 1;
        int k2p    = k;
        while (e != 0) {
            if ((e & 0x1) != 0) {
                result *= k2p;
            }
            k2p *= k2p;
            e = e >> 1;
        }

        return result;

    }

    /**
     * Raise an int to a long power.
     * @param k number to raise
     * @param e exponent (must be positive or null)
     * @return ke
     * @exception IllegalArgumentException if e is negative
     */
    public static int pow(final int k, long e)
            throws IllegalArgumentException {

        if (e < 0) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "cannot raise an integral value to a negative power ({0}^{1})",
                    k, e);
        }

        int result = 1;
        int k2p    = k;
        while (e != 0) {
            if ((e & 0x1) != 0) {
                result *= k2p;
            }
            k2p *= k2p;
            e = e >> 1;
        }

        return result;

    }

    /**
     * Raise a long to an int power.
     * @param k number to raise
     * @param e exponent (must be positive or null)
     * @return ke
     * @exception IllegalArgumentException if e is negative
     */
    public static long pow(final long k, int e)
            throws IllegalArgumentException {

        if (e < 0) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "cannot raise an integral value to a negative power ({0}^{1})",
                    k, e);
        }

        long result = 1l;
        long k2p    = k;
        while (e != 0) {
            if ((e & 0x1) != 0) {
                result *= k2p;
            }
            k2p *= k2p;
            e = e >> 1;
        }

        return result;

    }

    /**
     * Raise a long to a long power.
     * @param k number to raise
     * @param e exponent (must be positive or null)
     * @return ke
     * @exception IllegalArgumentException if e is negative
     */
    public static long pow(final long k, long e)
            throws IllegalArgumentException {

        if (e < 0) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "cannot raise an integral value to a negative power ({0}^{1})",
                    k, e);
        }

        long result = 1l;
        long k2p    = k;
        while (e != 0) {
            if ((e & 0x1) != 0) {
                result *= k2p;
            }
            k2p *= k2p;
            e = e >> 1;
        }

        return result;

    }

    /**
     * Raise a BigInteger to an int power.
     * @param k number to raise
     * @param e exponent (must be positive or null)
     * @return ke
     * @exception IllegalArgumentException if e is negative
     */
    public static BigInteger pow(final BigInteger k, int e)
            throws IllegalArgumentException {

        if (e < 0) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "cannot raise an integral value to a negative power ({0}^{1})",
                    k, e);
        }

        return k.pow(e);

    }

    /**
     * Raise a BigInteger to a long power.
     * @param k number to raise
     * @param e exponent (must be positive or null)
     * @return ke
     * @exception IllegalArgumentException if e is negative
     */
    public static BigInteger pow(final BigInteger k, long e)
            throws IllegalArgumentException {

        if (e < 0) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "cannot raise an integral value to a negative power ({0}^{1})",
                    k, e);
        }

        BigInteger result = BigInteger.ONE;
        BigInteger k2p    = k;
        while (e != 0) {
            if ((e & 0x1) != 0) {
                result = result.multiply(k2p);
            }
            k2p = k2p.multiply(k2p);
            e = e >> 1;
        }

        return result;

    }

    /**
     * Raise a BigInteger to a BigInteger power.
     * @param k number to raise
     * @param e exponent (must be positive or null)
     * @return ke
     * @exception IllegalArgumentException if e is negative
     */
    public static BigInteger pow(final BigInteger k, BigInteger e)
            throws IllegalArgumentException {

        if (e.compareTo(BigInteger.ZERO) < 0) {
            throw MathRuntimeException.createIllegalArgumentException(
                    "cannot raise an integral value to a negative power ({0}^{1})",
                    k, e);
        }

        BigInteger result = BigInteger.ONE;
        BigInteger k2p    = k;
        while (!BigInteger.ZERO.equals(e)) {
            if (e.testBit(0)) {
                result = result.multiply(k2p);
            }
            k2p = k2p.multiply(k2p);
            e = e.shiftRight(1);
        }

        return result;

    }

    /**
     * Calculates the L1 (sum of abs) distance between two points.
     *
     * @param p1 the first point
     * @param p2 the second point
     * @return the L1 distance between the two points
     */
    public static double distance1(double[] p1, double[] p2) {
        double sum = 0;
        for (int i = 0; i < p1.length; i++) {
            sum += Math.abs(p1[i] - p2[i]);
        }
        return sum;
    }

    /**
     * Calculates the L1 (sum of abs) distance between two points.
     *
     * @param p1 the first point
     * @param p2 the second point
     * @return the L1 distance between the two points
     */
    public static int distance1(int[] p1, int[] p2) {
        int sum = 0;
        for (int i = 0; i < p1.length; i++) {
            sum += Math.abs(p1[i] - p2[i]);
        }
        return sum;
    }

    /**
     * Calculates the L2 (Euclidean) distance between two points.
     *
     * @param p1 the first point
     * @param p2 the second point
     * @return the L2 distance between the two points
     */
    public static double distance(double[] p1, double[] p2) {
        double sum = 0;
        for (int i = 0; i < p1.length; i++) {
            final double dp = p1[i] - p2[i];
            sum += dp * dp;
        }
        return Math.sqrt(sum);
    }

    /**
     * Calculates the L2 (Euclidean) distance between two points.
     *
     * @param p1 the first point
     * @param p2 the second point
     * @return the L2 distance between the two points
     */
    public static double distance(int[] p1, int[] p2) {
        double sum = 0;
        for (int i = 0; i < p1.length; i++) {
            final double dp = p1[i] - p2[i];
            sum += dp * dp;
        }
        return Math.sqrt(sum);
    }

    /**
     * Calculates the L∞ (max of abs) distance between two points.
     *
     * @param p1 the first point
     * @param p2 the second point
     * @return the L∞ distance between the two points
     */
    public static double distanceInf(double[] p1, double[] p2) {
        double max = 0;
        for (int i = 0; i < p1.length; i++) {
            max = Math.max(max, Math.abs(p1[i] - p2[i]));
        }
        return max;
    }

    /**
     * Calculates the L∞ (max of abs) distance between two points.
     *
     * @param p1 the first point
     * @param p2 the second point
     * @return the L∞ distance between the two points
     */
    public static int distanceInf(int[] p1, int[] p2) {
        int max = 0;
        for (int i = 0; i < p1.length; i++) {
            max = Math.max(max, Math.abs(p1[i] - p2[i]));
        }
        return max;
    }


}




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