/*
 * Java Genetic Algorithm Library (jenetics-7.1.0).
 * Copyright (c) 2007-2022 Franz Wilhelmstötter
 *
 * 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.
 *
 * Author:
 *    Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
 */
package io.jenetics.internal.math;

import static java.lang.Double.doubleToLongBits;
import static java.lang.Double.min;

import io.jenetics.stat.LongSummary;

/**
 * This object contains mathematical helper functions.
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @since 1.0
 * @version 5.2
 */
public final class Basics {
        private Basics() {}

        /**
         * Normalize the given double array, so that it sum to one. The
         * normalization is performed in place and the same {@code values} are
         * returned.
         *
         * @param values the values to normalize.
         * @return the {@code values} array.
         * @throws NullPointerException if the given double array is {@code null}.
         */
        public static double[] normalize(final double[] values) {
                final double sum = 1.0/DoubleAdder.sum(values);
                for (int i = values.length; --i >= 0;) {
                        values[i] = values[i]*sum;
                }

                return values;
        }

        public static double[] normalize(final long[] values) {
                final double[] result = new double[values.length];
                final double sum = 1.0/LongSummary.sum(values);
                for (int i = values.length; --i >= 0;) {
                        result[i] = values[i]*sum;
                }

                return result;
        }

        /**
         * Component wise division of the given double array.
         *
         * @param values the double values to divide.
         * @param divisor the divisor.
         * @throws NullPointerException if the given double array is {@code null}.
         */
        public static void divide(final double[] values, final double divisor) {
                for (int i = values.length; --i >= 0;) {
                        values[i] /= divisor;
                }
        }

        /**
         * Binary exponentiation algorithm.
         *
         * @param b the base number.
         * @param e the exponent.
         * @return {@code b^e}.
         */
        public static long pow(final long b, final long e) {
                long base = b;
                long exp = e;
                long result = 1;

                while (exp != 0) {
                        if ((exp & 1) != 0) {
                                result *= base;
                        }
                        exp >>>= 1;
                        base *= base;
                }

                return result;
        }

        public static boolean isMultiplicationSave(final int a, final int b) {
                final long m = (long)a*(long)b;
                return (int)m == m;
        }

        /**
         * <i>Clamping</i> a value between a pair of boundary values.
         * <i>Note: using clamp with floating point numbers may give unexpected
         * results if one of the values is {@code NaN}.</i>
         *
         * @param v the value to <i>clamp</i>
         * @param lo the lower bound.
         * @param hi the upper bound.
         * @return The clamped value:
         *        <ul>
         *            <li>{@code lo if v < lo}</li>
         *            <li>{@code hi if hi < v}</li>
         *            <li>{@code otherwise, v}</li>
         *        </ul>
         */
        public static double clamp(final double v, final double lo, final double hi) {
                return v < lo ? lo : min(v, hi);
        }

        /**
         * Return the <a href="http://en.wikipedia.org/wiki/Unit_in_the_last_place">ULP</a>
         * distance of the given two double values.
         *
         * @param a first double.
         * @param b second double.
         * @return the ULP distance.
         * @throws ArithmeticException if the distance doesn't fit in a long value.
         */
        public static long ulpDistance(final double a, final double b) {
                return Math.subtractExact(ulpPosition(a), ulpPosition(b));
        }

        /**
         * Calculating the <a href="http://en.wikipedia.org/wiki/Unit_in_the_last_place">ULP</a>
         * position of a double number.
         *
         * <pre>{@code
         * double a = 0.0;
         * for (int i = 0; i < 10; ++i) {
         *     a = Math.nextAfter(a, Double.POSITIVE_INFINITY);
         * }
         *
         * for (int i = 0; i < 19; ++i) {
         *     a = Math.nextAfter(a, Double.NEGATIVE_INFINITY);
         *     System.out.println(
         *          a + "\t" + ulpPosition(a) + "\t" + ulpDistance(0.0, a)
         *     );
         * }
         * }</pre>
         *
         * The code fragment above will create the following output:
         * <pre>
         *   4.4E-323    9  9
         *   4.0E-323    8  8
         *   3.5E-323    7  7
         *   3.0E-323    6  6
         *   2.5E-323    5  5
         *   2.0E-323    4  4
         *   1.5E-323    3  3
         *   1.0E-323    2  2
         *   4.9E-324    1  1
         *   0.0         0  0
         *  -4.9E-324   -1  1
         *  -1.0E-323   -2  2
         *  -1.5E-323   -3  3
         *  -2.0E-323   -4  4
         *  -2.5E-323   -5  5
         *  -3.0E-323   -6  6
         *  -3.5E-323   -7  7
         *  -4.0E-323   -8  8
         *  -4.4E-323   -9  9
         * </pre>
         *
         * @param a the double number.
         * @return the ULP position.
         */
        public static long ulpPosition(final double a) {
                long t = doubleToLongBits(a);
                if (t < 0) {
                        t = Long.MIN_VALUE - t;
                }
                return t;
        }

}