pcg_basic.c

/*
 * PCG Random Number Generation for C.
 *
 * Copyright 2014 Melissa O'Neill <oneill@pcg-random.org>
 *
 * 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.
 *
 * For additional information about the PCG random number generation scheme,
 * including its license and other licensing options, visit
 *
 *       http://www.pcg-random.org
 */

#include "pcg_basic.h"

void pcg32_srandom_r(pcg32_random_t* rng, uint64_t initial_state, uint64_t initseq) {
    rng->state = 0U;
    rng->inc = (initseq << 1u) | 1u;
    pcg32_random_r(rng);
    rng->state += initial_state;
    pcg32_random_r(rng);
}

uint32_t pcg32_random_r(pcg32_random_t* rng) {
    uint64_t oldstate = rng->state;
    rng->state = oldstate * 6364136223846793005ULL + rng->inc;
    uint32_t xorshifted = (uint32_t)(((oldstate >> 18u) ^ oldstate) >> 27u);
    uint32_t rot = (uint32_t)(oldstate >> 59u);
    return (xorshifted >> rot) | (xorshifted << ((~rot + 1u) & 31)); /* was (xorshifted >> rot) | (xorshifted << ((-rot) & 31)) */
}