src/decaf/src/main/decaf/util/Random.cpp

/*
 * 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.
 */

#include "Random.h"

#include <decaf/util/Date.h>

using namespace decaf;
using namespace decaf::util;
using namespace decaf::lang;

unsigned long long Random::multiplier = 0x5deece66dLL;

////////////////////////////////////////////////////////////////////////////////
Random::Random() {
    setSeed(Date::getCurrentTimeMilliseconds());
}

////////////////////////////////////////////////////////////////////////////////
Random::Random( unsigned long long seed ) {
    setSeed(seed);
}

////////////////////////////////////////////////////////////////////////////////
bool Random::nextBoolean() {
    return next(1) != 0;
}

////////////////////////////////////////////////////////////////////////////////
void Random::nextBytes( std::vector<unsigned char>& buf ) {
    int rand = 0;
    std::size_t count = 0, loop = 0;
    while (count < buf.size()) {
        if (loop == 0) {
            rand = nextInt();
            loop = 3;
        } else {
            loop--;
        }
        buf[count++] = (unsigned char) rand;
        rand >>= 8;
    }
}

////////////////////////////////////////////////////////////////////////////////
double Random::nextDouble() {
    // was: return ((((long long) next(26) << 27) + next(27)) / (double) (1L << 53));
    long long divisor = 1LL;
    divisor <<= 31;
    divisor <<= 22;
    return ((((long long) next(26) << 27) + next(27)) / (double) divisor);
}

////////////////////////////////////////////////////////////////////////////////
float Random::nextFloat() {
    return (next(24) / 16777216.0f);
}

////////////////////////////////////////////////////////////////////////////////
double Random::nextGaussian() {
    if (haveNextNextGaussian) {
        // if X1 has been returned, return the second Gaussian
        haveNextNextGaussian = false;
        return nextNextGaussian;
    }

    double v1, v2, s;
    do {
        // Generates two independent random variables U1, U2
        v1 = 2 * nextDouble() - 1;
        v2 = 2 * nextDouble() - 1;
        s = v1 * v1 + v2 * v2;
    } while (s >= 1);
    double norm = std::sqrt(-2 * std::log(s) / s);
    // should that not be norm instead of multiplier ?
    nextNextGaussian = v2 * norm;
    haveNextNextGaussian = true;
    // should that not be norm instead of multiplier ?
    return v1 * norm;
}

////////////////////////////////////////////////////////////////////////////////
int Random::nextInt() {
    return next(32);
}

////////////////////////////////////////////////////////////////////////////////
int Random::nextInt( int n ) throw( exceptions::IllegalArgumentException ) {
    if (n > 0) {
        if ((n & -n) == n) {
            return (int) ((n * (long long) next(31)) >> 31);
        }
        int bits, val;
        do {
            bits = next(31);
            val = bits % n;
        } while (bits - val + (n - 1) < 0);
        return val;
    }
    throw exceptions::IllegalArgumentException();
}

////////////////////////////////////////////////////////////////////////////////
long long Random::nextLong() {
    return ((long long) next(32) << 32) + next(32);
}

////////////////////////////////////////////////////////////////////////////////
void Random::setSeed( unsigned long long seed ) {
    // was this->seed = (seed ^ multiplier) & ((1L << 48) - 1);
    unsigned long long mask = 1ULL;
    mask <<= 31;
    mask <<= 17;
    this->seed = (seed ^ multiplier) & (mask - 1);
    haveNextNextGaussian = false;
}

////////////////////////////////////////////////////////////////////////////////
int Random::next( int bits ) {
    // was: seed = (seed * multiplier + 0xbL) & ((1L << 48) - 1);
    long long mask = 1L;
    mask <<= 31;
    mask <<= 17;
    seed = (seed * multiplier + 0xbL) & (mask - 1);
    // was: return (int) (seed >>> (48 - bits));
    return (int) (seed >> (48 - bits));
}