BEGIN LICENSE BLOCK *****
Version: EPL 2.0/GPL 2.0/LGPL 2.1
The contents of this file are subject to the Eclipse Public
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.eclipse.org/legal/epl-v20.html
Software distributed under the License is distributed on an "AS
IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
implied. See the License for the specific language governing
rights and limitations under the License.
Alternatively, the contents of this file may be used under the terms of
either of the GNU General Public License Version 2 or later (the "GPL"),
or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
in which case the provisions of the GPL or the LGPL are applicable instead
of those above. If you wish to allow use of your version of this file only
under the terms of either the GPL or the LGPL, and not to allow others to
use your version of this file under the terms of the EPL, indicate your
decision by deleting the provisions above and replace them with the notice
and other provisions required by the GPL or the LGPL. If you do not delete
the provisions above, a recipient may use your version of this file under
the terms of any one of the EPL, the GPL or the LGPL.
END LICENSE BLOCK /***** BEGIN LICENSE BLOCK *****
 * Version: EPL 2.0/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Eclipse Public
 * 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.eclipse.org/legal/epl-v20.html
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the EPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the EPL, the GPL or the LGPL.
 ***** END LICENSE BLOCK *****/

package org.jruby.util;

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

public class Random {
    public static final int N = 624;
    private static final int M = 397;
    private static final int MATRIX_A = 0x9908b0df; /* constant vector a */
    private static final int UMASK = 0x80000000; /* most significant w-r bits */
    private static final int LMASK = 0x7fffffff; /* least significant r bits */

    private static int MIXBITS(int u, int v) {
        return (u & UMASK) | (v & LMASK);
    }

    private static int TWIST(int u, int v) {
        return (MIXBITS(u, v) >>> 1) ^ (((v & 1) != 0) ? MATRIX_A : 0);
    }

    private final int[] state = new int[N];
    private int left = 1;

    public Random() {
    }

    public Random(int s) {
        initGenrand(s);
    }

    public Random(int[] initKey) {
        initByArray(initKey);
    }

    public Random(Random orig) {
        System.arraycopy(orig.state, 0, this.state, 0, this.state.length);
        this.left = orig.left;
    }

    public Random(int[] state, int left) {
        if (state.length != this.state.length) {
            throw new IllegalStateException("wrong state length: " + state.length);
        }
        System.arraycopy(state, 0, this.state, 0, this.state.length);
        this.left = left;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) return true;
        if (!(obj instanceof Random)) return false;
        Random rhs = (Random) obj;
        return (left == rhs.left) && Arrays.equals(state, rhs.state);
    }

    @Override
    public int hashCode() {
        // Using 17 as the initializer, 37 as the multiplier.
        return (629 + left) * 37 + Arrays.hashCode(state);
    }
    
    private void initGenrand(int s) {
        state[0] = s;
        for (int j = 1; j < N; j++) {
            state[j] = (1812433253 * (state[j - 1] ^ (state[j - 1] >>> 30)) + j);
        }
        left = 1;
    }

    private void initByArray(int[] initKey) {
        initGenrand(19650218);
        int len = initKey.length;
        int i = 1;
        int j = 0;
        int k = N > len ? N : len;
        for (; k > 0; k--) {
            state[i] = (state[i] ^ ((state[i - 1] ^ (state[i - 1] >>> 30)) * 1664525)) + initKey[j]
                    + j;
            i++;
            j++;
            if (i >= N) {
                state[0] = state[N - 1];
                i = 1;
            }
            if (j >= len) {
                j = 0;
            }
        }
        for (k = N - 1; k > 0; k--) {
            state[i] = (state[i] ^ ((state[i - 1] ^ (state[i - 1] >>> 30)) * 1566083941)) - i;
            i++;
            if (i >= N) {
                state[0] = state[N - 1];
                i = 1;
            }
        }
        state[0] = 0x80000000;
    }

    private void nextState() {
        int p = 0;

        left = N;

        for (int j = N - M + 1; --j > 0; p++) {
            state[p] = state[p + M] ^ TWIST(state[p + 0], state[p + 1]);
        }

        for (int j = M; --j > 0; p++) {
            state[p] = state[p + M - N] ^ TWIST(state[p + 0], state[p + 1]);
        }

        state[p] = state[p + M - N] ^ TWIST(state[p + 0], state[0]);
    }

    public int genrandInt32() {
        int y;

        synchronized (this) {
            if (--left <= 0)
                nextState();

            y = state[N - left];
        }

        /* Tempering */
        y ^= (y >>> 11);
        y ^= (y << 7) & 0x9d2c5680L;
        y ^= (y << 15) & 0xefc60000L;
        y ^= (y >>> 18);

        return y;
    }

    public double genrandReal() {
        int a = genrandInt32() >>> 5;
        int b = genrandInt32() >>> 6;
        return (a * 67108864.0 + b) * (1.0 / 9007199254740992.0);
    }

    public double genrandReal2() {
        int a = genrandInt32();
        int b = genrandInt32();
        return intPairToRealInclusive(a, b);
    }

    private static final BigInteger INTPAIR_CONST = BigInteger.valueOf((1L << 53) + 1);
    private static final double LDEXP_CONST = Math.pow(2.0, -53);

    // c: ldexp((a<< 32)|b) * ((1<<53)+1) >> 64, -53)
    // TODO: not enough prec...
    private double intPairToRealInclusive(int a, int b) {
        BigInteger c = BigInteger.valueOf(a & 0xffffffffL);
        BigInteger d = BigInteger.valueOf(b & 0xffffffffL);
        return c.shiftLeft(32).or(d).multiply(INTPAIR_CONST).shiftRight(64).doubleValue()
                * LDEXP_CONST;
    }

    public int[] getState() {
        return state;
    }

    public int getLeft() {
        return left;
    }
}