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package java.util.random;

import java.math.BigInteger;

import java.util.concurrent.atomic.AtomicLong;

import java.util.random.RandomGenerator.LeapableGenerator;

import java.util.random.RandomSupport.AbstractArbitrarilyJumpableGenerator;

/**

 * A generator of uniform pseudorandom values applicable for use in

 * (among other contexts) isolated parallel computations that may

 * generate subtasks.  Class {@link MRG32k3a} implements

 * interfaces {@link RandomGenerator} and {@link AbstractArbitrarilyJumpableGenerator},

 * and therefore supports methods for producing pseudorandomly chosen

 * numbers of type {@code int}, {@code long}, {@code float}, and {@code double}

 * as well as creating new {@link Xoroshiro128PlusMRG32k3a} objects

 * by "jumping" or "leaping".

 * <p>

 * Instances {@link Xoroshiro128Plus} are <em>not</em> thread-safe.

 * They are designed to be used so that each thread as its own instance.

 * The methods {@link #jump} and {@link #leap} and {@link #jumps} and {@link #leaps}

 * can be used to construct new instances of {@link Xoroshiro128Plus} that traverse

 * other parts of the state cycle.

 * <p>

 * Instances of {@link MRG32k3a} are not cryptographically

 * secure.  Consider instead using {@link java.security.SecureRandom}

 * in security-sensitive applications. Additionally,

 * default-constructed instances do not use a cryptographically random

 * seed unless the {@linkplain System#getProperty system property}

 * {@code java.util.secureRandomSeed} is set to {@code true}.

 *

 * @since 14

 */

public final class MRG32k3a extends AbstractArbitrarilyJumpableGenerator {

    /*

     * Implementation Overview.

     *

     * See http://simul.iro.umontreal.ca/rng/MRG32k3a.c .

     *

     * File organization: First the non-public methods that constitute

     * the main algorithm, then the main public methods, followed by

     * some custom spliterator classes needed for stream methods.

     */

    private final static double NORM1 = 2.328306549295728e-10;

    private final static double NORM2 = 2.328318824698632e-10;

    private final static double M1 =   4294967087.0;

    private final static double M2 =   4294944443.0;

    private final static double A12 =     1403580.0;

    private final static double A13N =     810728.0;

    private final static double A21 =      527612.0;

    private final static double A23N =    1370589.0;

    private final static int M1_DEFICIT = 209;

    /**

     * The per-instance state.

     The seeds for s10, s11, s12 must be integers in [0, m1 - 1] and not all 0.

     The seeds for s20, s21, s22 must be integers in [0, m2 - 1] and not all 0.

     */

    private double s10, s11, s12,

                   s20, s21, s22;

    /**

     * The seed generator for default constructors.

     */

    private static final AtomicLong DEFAULT_GEN =

        new AtomicLong(RandomSupport.initialSeed());

    /*

      32-bits Random number generator U(0,1): MRG32k3a

      Author: Pierre L'Ecuyer,

      Source: Good Parameter Sets for Combined Multiple Recursive Random

           Number Generators,

           Shorter version in Operations Research,

           47, 1 (1999), 159--164.

           ---------------------------------------------------------

    */

    private void nextState() {

        /* Component 1 */

        double p1 = A12 * s11 - A13N * s10;

        double k1 = p1 / M1;   p1 -= k1 * M1;   if (p1 < 0.0) p1 += M1;

        s10 = s11;   s11 = s12;   s12 = p1;

        /* Component 2 */

        double p2 = A21 * s22 - A23N * s20;

        double k2 = p2 / M2;   p2 -= k2 * M2;   if (p2 < 0.0) p2 += M2;

        s20 = s21;   s21 = s22;   s22 = p2;

    }

    /**

     * The form of nextInt used by IntStream Spliterators.

     * Exactly the same as long version, except for types.

     *

     * @param origin the least value, unless greater than bound

     * @param bound the upper bound (exclusive), must not equal origin

     *

     * @return a pseudorandom value

     */

    private int internalNextInt(int origin, int bound) {

        if (origin < bound) {

            final int n = bound - origin;

            final int m = n - 1;

            if (n > 0) {

                int r;

                for (int u = (int)nextDouble() >>> 1;

                     u + m + ((M1_DEFICIT + 1) >>> 1) - (r = u % n) < 0;

                     u = (int)nextDouble() >>> 1)

                    ;

                return (r + origin);

            } else {

                return RandomSupport.boundedNextInt(this, origin, bound);

            }

        } else {

            return nextInt();

        }

    }

    private int internalNextInt(int bound) {

        // Specialize internalNextInt for origin == 0, bound > 0

        final int n = bound;

        final int m = n - 1;

        int r;

        for (int u = (int)nextDouble() >>> 1;

             u + m + ((M1_DEFICIT + 1) >>> 1) - (r = u % n) < 0;

             u = (int)nextDouble() >>> 1)

            ;

        return r;

    }

    /**

     * All arguments must be known to be nonnegative integral values

     * less than the appropriate modulus.

     */

    private MRG32k3a(double s10, double s11, double s12,

                     double s20, double s21, double s22) {

        this.s10 = s10; this.s11 = s11; this.s12 = s12;

        this.s20 = s20; this.s21 = s21; this.s22 = s22;

        if ((s10 == 0.0) && (s11 == 0.0) && (s12 == 0.0)) {

            this.s10 = this.s11 = this.s12 = 12345.0;

        }

        if ((s20 == 0.0) && (s21 == 0.0) && (s22 == 0.0)) {

            this.s20 = this.s21 = this.s21 = 12345.0;

        }

    }

    /* ---------------- public methods ---------------- */

    /**

     * Creates a new MRG32k3a instance using six specified {@code int}

     * initial seed values. MRG32k3a instances created with the same

     * seeds in the same program generate identical sequences of values.

     * If all six seed values are zero, the generator is seeded to a

     * widely used initialization of MRG32k3a: all six state variables

     * are set to 12345.

     *

     * @param s10 the first seed value for the first subgenerator

     * @param s11 the second seed value for the first subgenerator

     * @param s12 the third seed value for the first subgenerator

     * @param s20 the first seed value for the second subgenerator

     * @param s21 the second seed value for the second subgenerator

     * @param s22 the third seed value for the second subgenerator

     */

    public MRG32k3a(int s10, int s11, int s12,

                    int s20, int s21, int s22) {

        this(((double)(((long)s10) & 0x00000000ffffffffL)) % M1,

             ((double)(((long)s11) & 0x00000000ffffffffL)) % M1,

             ((double)(((long)s12) & 0x00000000ffffffffL)) % M1,

             ((double)(((long)s20) & 0x00000000ffffffffL)) % M2,

             ((double)(((long)s21) & 0x00000000ffffffffL)) % M2,

             ((double)(((long)s22) & 0x00000000ffffffffL)) % M2);

    }

    /**

     * Creates a new MRG32k3a instance using the specified

     * initial seed. MRG32k3a instances created with the same

     * seed in the same program generate identical sequences of values.

     * An argument of 0 seeds the generator to a widely used initialization

     * of MRG32k3a: all six state variables are set to 12345.

     *

     * @param seed the initial seed

     */

    public MRG32k3a(long seed) {

        this((double)((seed & 0x7FF) + 12345),

             (double)(((seed >>> 11) & 0x7FF) + 12345),

             (double)(((seed >>> 22) & 0x7FF) + 12345),

             (double)(((seed >>> 33) & 0x7FF) + 12345),

             (double)(((seed >>> 44) & 0x7FF) + 12345),

             (double)((seed >>> 55) + 12345));

    }

    /**

     * Creates a new MRG32k3a instance that is likely to

     * generate sequences of values that are statistically independent

     * of those of any other instances in the current program; and

     * may, and typically does, vary across program invocations.

     */

    public MRG32k3a() {

        this(DEFAULT_GEN.getAndAdd(RandomSupport.GOLDEN_RATIO_64));

    }

    /**

     * Creates a new instance of {@link Xoshiro256StarStar} using the specified array of

     * initial seed bytes. Instances of {@link Xoshiro256StarStar} created with the same

     * seed array in the same program execution generate identical sequences of values.

     *

     * @param seed the initial seed

     */

    public MRG32k3a(byte[] seed) {

        // Convert the seed to 6 int values.

        int[] data = RandomSupport.convertSeedBytesToInts(seed, 6, 0);

        int s10 = data[0], s11 = data[1], s12 = data[2];

        int s20 = data[3], s21 = data[4], s22 = data[5];

        this.s10 = ((double)(((long)s10) & 0x00000000ffffffffL)) % M1;

        this.s11 = ((double)(((long)s11) & 0x00000000ffffffffL)) % M1;

        this.s12 = ((double)(((long)s12) & 0x00000000ffffffffL)) % M1;

        this.s20 = ((double)(((long)s20) & 0x00000000ffffffffL)) % M2;

        this.s21 = ((double)(((long)s21) & 0x00000000ffffffffL)) % M2;

        this.s22 = ((double)(((long)s22) & 0x00000000ffffffffL)) % M2;

        if ((s10 == 0.0) && (s11 == 0.0) && (s12 == 0.0)) {

            this.s10 = this.s11 = this.s12 = 12345.0;

        }

        if ((s20 == 0.0) && (s21 == 0.0) && (s22 == 0.0)) {

            this.s20 = this.s21 = this.s21 = 12345.0;

        }

    }

    public MRG32k3a copy() {

        return new MRG32k3a(s10, s11, s12, s20, s21, s22);

    }

    /**

     * Returns a pseudorandom {@code double} value between zero

     * (exclusive) and one (exclusive).

     *

     * @return a pseudorandom {@code double} value between zero

     *         (exclusive) and one (exclusive)

     */

    public double nextOpenDouble() {

        nextState();

        double p1 = s12, p2 = s22;

        if (p1 <= p2)

            return ((p1 - p2 + M1) * NORM1);

        else

            return ((p1 - p2) * NORM1);

    }

    /**

     * Returns a pseudorandom {@code double} value between zero

     * (inclusive) and one (exclusive).

     *

     * @return a pseudorandom {@code double} value between zero

     *         (inclusive) and one (exclusive)

     */

    public double nextDouble() {

        nextState();

        double p1 = s12, p2 = s22;

        final double p = p1 * NORM1 - p2 * NORM2;

        if (p < 0.0) return (p + 1.0);

        else return p;

    }

    /**

     * Returns a pseudorandom {@code float} value between zero

     * (inclusive) and one (exclusive).

     *

     * @return a pseudorandom {@code float} value between zero

     *         (inclusive) and one (exclusive)

     */

    public float nextFloat() {

        return (float)nextDouble();

    }

    /**

     * Returns a pseudorandom {@code int} value.

     *

     * @return a pseudorandom {@code int} value

     */

    public int nextInt() {

        return (internalNextInt(0x10000) << 16) | internalNextInt(0x10000);

    }

    /**

     * Returns a pseudorandom {@code long} value.

     *

     * @return a pseudorandom {@code long} value

     */

    public long nextLong() {

         return (((long)internalNextInt(0x200000) << 43) |

                ((long)internalNextInt(0x200000) << 22) |

                ((long)internalNextInt(0x400000)));

    }

    // Period is (m1**3 - 1)(m2**3 - 1)/2, or approximately 2**191.

    static BigInteger calculateThePeriod() {

        BigInteger bigm1 = BigInteger.valueOf((long)M1);

        BigInteger bigm2 = BigInteger.valueOf((long)M2);

        BigInteger t1 = bigm1.multiply(bigm1).multiply(bigm1).subtract(BigInteger.ONE);

        BigInteger t2 = bigm2.multiply(bigm2).multiply(bigm2).subtract(BigInteger.ONE);

        return t1.shiftRight(1).multiply(t2);

    }

    static final BigInteger PERIOD = calculateThePeriod();

    public BigInteger period() {

        return PERIOD;

    }

    // Jump and leap distances recommended in Section 1.3 of this paper:

    // Pierre L'Ecuyer, Richard Simard, E. Jack Chen, and W. David Kelton.

    // An Object-Oriented Random-Number Package with Many Long Streams and Substreams.

    // Operations Research 50, 6 (Nov--Dec 2002), 1073--1075.

    public double defaultJumpDistance() {

        return 0x1.0p76;   // 2**76

    }

    public double defaultLeapDistance() {

        return 0x1.0p127;   // 2**127

    }

    public void jump(double distance) {

        if (distance < 0.0 || Double.isInfinite(distance) || distance != Math.floor(distance))

            throw new IllegalArgumentException("jump distance must be a nonnegative finite integer");

            // We will compute a jump transformation (s => M s) for each LCG.

            // We initialize each transformation to the identity transformation.

            // Each will be turned into the d'th power of the corresponding base transformation.

        long m1_00 = 1, m1_01 = 0, m1_02 = 0,

             m1_10 = 0, m1_11 = 1, m1_12 = 0,

             m1_20 = 0, m1_21 = 0, m1_22 = 1;

        long m2_00 = 1, m2_01 = 0, m2_02 = 0,

             m2_10 = 0, m2_11 = 1, m2_12 = 0,

             m2_20 = 0, m2_21 = 0, m2_22 = 1;

        // These are the base transformations, which will be repeatedly squared,

        // and composed with the computed transformations for each 1-bit in distance.

        long t1_00 = 0,           t1_01 = 1,         t1_02 = 0,

             t1_10 = 0,           t1_11 = 0,         t1_12 = 1,

             t1_20 = -(long)A13N, t1_21 = (long)A12, t1_22 = 0;

        long t2_00 = 0,           t2_01 = 1,         t2_02 = 0,

             t2_10 = 0,           t2_11 = 0,         t2_12 = 1,

             t2_20 = -(long)A23N, t2_21 = (long)A21, t2_22 = 0;

        while (distance > 0.0) {

            final double dhalf = 0.5 * distance;

            if (Math.floor(dhalf) != dhalf) {

                // distance is odd: accumulate current squaring

                final long n1_00 = m1_00 * t1_00 + m1_01 * t1_10 + m1_02 * t1_20;

                final long n1_01 = m1_00 * t1_01 + m1_01 * t1_11 + m1_02 * t1_21;

                final long n1_02 = m1_00 * t1_02 + m1_01 * t1_12 + m1_02 * t1_22;

                final long n1_10 = m1_10 * t1_00 + m1_11 * t1_10 + m1_12 * t1_20;

                final long n1_11 = m1_10 * t1_01 + m1_11 * t1_11 + m1_12 * t1_21;

                final long n1_12 = m1_10 * t1_02 + m1_11 * t1_12 + m1_12 * t1_22;

                final long n1_20 = m1_20 * t1_00 + m1_21 * t1_10 + m1_22 * t1_20;

                final long n1_21 = m1_20 * t1_01 + m1_21 * t1_11 + m1_22 * t1_21;

                final long n1_22 = m1_20 * t1_02 + m1_21 * t1_12 + m1_22 * t1_22;

                m1_00 = Math.floorMod(n1_00, (long)M1);

                m1_01 = Math.floorMod(n1_01, (long)M1);

                m1_02 = Math.floorMod(n1_02, (long)M1);

                m1_10 = Math.floorMod(n1_10, (long)M1);

                m1_11 = Math.floorMod(n1_11, (long)M1);

                m1_12 = Math.floorMod(n1_12, (long)M1);

                m1_20 = Math.floorMod(n1_20, (long)M1);

                m1_21 = Math.floorMod(n1_21, (long)M1);

                m1_22 = Math.floorMod(n1_22, (long)M1);

                final long n2_00 = m2_00 * t2_00 + m2_01 * t2_10 + m2_02 * t2_20;

                final long n2_01 = m2_00 * t2_01 + m2_01 * t2_11 + m2_02 * t2_21;

                final long n2_02 = m2_00 * t2_02 + m2_01 * t2_12 + m2_02 * t2_22;

                final long n2_10 = m2_10 * t2_00 + m2_11 * t2_10 + m2_12 * t2_20;

                final long n2_11 = m2_10 * t2_01 + m2_11 * t2_11 + m2_12 * t2_21;

                final long n2_12 = m2_10 * t2_02 + m2_11 * t2_12 + m2_12 * t2_22;

                final long n2_20 = m2_20 * t2_00 + m2_21 * t2_10 + m2_22 * t2_20;

                final long n2_21 = m2_20 * t2_01 + m2_21 * t2_11 + m2_22 * t2_21;

                final long n2_22 = m2_20 * t2_02 + m2_21 * t2_12 + m2_22 * t2_22;

                m2_00 = Math.floorMod(n2_00, (long)M2);

                m2_01 = Math.floorMod(n2_01, (long)M2);

                m2_02 = Math.floorMod(n2_02, (long)M2);

                m2_10 = Math.floorMod(n2_10, (long)M2);

                m2_11 = Math.floorMod(n2_11, (long)M2);

                m2_12 = Math.floorMod(n2_12, (long)M2);

                m2_20 = Math.floorMod(n2_20, (long)M2);

                m2_21 = Math.floorMod(n2_21, (long)M2);

                m2_22 = Math.floorMod(n2_22, (long)M2);

            }

            // Square the base transformations.

            {

                final long z1_00 = m1_00 * m1_00 + m1_01 * m1_10 + m1_02 * m1_20;

                final long z1_01 = m1_00 * m1_01 + m1_01 * m1_11 + m1_02 * m1_21;

                final long z1_02 = m1_00 * m1_02 + m1_01 * m1_12 + m1_02 * m1_22;

                final long z1_10 = m1_10 * m1_00 + m1_11 * m1_10 + m1_12 * m1_20;

                final long z1_11 = m1_10 * m1_01 + m1_11 * m1_11 + m1_12 * m1_21;

                final long z1_12 = m1_10 * m1_02 + m1_11 * m1_12 + m1_12 * m1_22;

                final long z1_20 = m1_20 * m1_00 + m1_21 * m1_10 + m1_22 * m1_20;

                final long z1_21 = m1_20 * m1_01 + m1_21 * m1_11 + m1_22 * m1_21;

                final long z1_22 = m1_20 * m1_02 + m1_21 * m1_12 + m1_22 * m1_22;

                m1_00 = Math.floorMod(z1_00, (long)M1);

                m1_01 = Math.floorMod(z1_01, (long)M1);

                m1_02 = Math.floorMod(z1_02, (long)M1);

                m1_10 = Math.floorMod(z1_10, (long)M1);

                m1_11 = Math.floorMod(z1_11, (long)M1);

                m1_12 = Math.floorMod(z1_12, (long)M1);

                m1_20 = Math.floorMod(z1_20, (long)M1);

                m1_21 = Math.floorMod(z1_21, (long)M1);

                m1_22 = Math.floorMod(z1_22, (long)M1);

                final long z2_00 = m2_00 * m2_00 + m2_01 * m2_10 + m2_02 * m2_20;

                final long z2_01 = m2_00 * m2_01 + m2_01 * m2_11 + m2_02 * m2_21;

                final long z2_02 = m2_00 * m2_02 + m2_01 * m2_12 + m2_02 * m2_22;

                final long z2_10 = m2_10 * m2_00 + m2_11 * m2_10 + m2_12 * m2_20;

                final long z2_11 = m2_10 * m2_01 + m2_11 * m2_11 + m2_12 * m2_21;

                final long z2_12 = m2_10 * m2_02 + m2_11 * m2_12 + m2_12 * m2_22;

                final long z2_20 = m2_20 * m2_00 + m2_21 * m2_10 + m2_22 * m2_20;

                final long z2_21 = m2_20 * m2_01 + m2_21 * m2_11 + m2_22 * m2_21;

                final long z2_22 = m2_20 * m2_02 + m2_21 * m2_12 + m2_22 * m2_22;

                m2_00 = Math.floorMod(z2_00, (long)M2);

                m2_01 = Math.floorMod(z2_01, (long)M2);

                m2_02 = Math.floorMod(z2_02, (long)M2);

                m2_10 = Math.floorMod(z2_10, (long)M2);

                m2_11 = Math.floorMod(z2_11, (long)M2);

                m2_12 = Math.floorMod(z2_12, (long)M2);

                m2_20 = Math.floorMod(z2_20, (long)M2);

                m2_21 = Math.floorMod(z2_21, (long)M2);

                m2_22 = Math.floorMod(z2_22, (long)M2);

            }

            // Divide distance by 2.

            distance = dhalf;

        }

        final long w10 = m1_00 * (long)s10 + m1_01 * (long)s11 + m1_02 * (long)s12;

        final long w11 = m1_10 * (long)s10 + m1_11 * (long)s11 + m1_12 * (long)s12;

        final long w12 = m1_20 * (long)s10 + m1_21 * (long)s11 + m1_22 * (long)s12;

        s10 = Math.floorMod(w10, (long)M1);

        s11 = Math.floorMod(w11, (long)M1);

        s12 = Math.floorMod(w12, (long)M1);

        final long w20 = m2_00 * (long)s20 + m2_01 * (long)s21 + m2_02 * (long)s22;

        final long w21 = m2_10 * (long)s20 + m2_11 * (long)s21 + m2_12 * (long)s22;

        final long w22 = m2_20 * (long)s20 + m2_21 * (long)s21 + m2_22 * (long)s22;

        s20 = Math.floorMod(w20, (long)M2);

        s21 = Math.floorMod(w21, (long)M2);

        s22 = Math.floorMod(w22, (long)M2);

    }

    /**

     * Alter the state of this pseudorandom number generator so as to

     * jump forward a distance equal to 2<sup>{@code logDistance}</sup>

     * within its state cycle.

     *

     * @param logDistance the base-2 logarithm of the distance to jump

     *        forward within the state cycle.  Must be non-negative and

     *        not greater than 192.

     *

     * @throws IllegalArgumentException if {@code logDistance} is

     *         less than zero or 2<sup>{@code logDistance}</sup> is

     *         greater than the period of this generator

     */

    public void jumpPowerOfTwo(int logDistance) {

        if (logDistance < 0 || logDistance > 192)

            throw new IllegalArgumentException("logDistance must be non-negative and not greater than 192");

        jump(Math.scalb(1.0, logDistance));

    }

}