source: azure_iot_hub/trunk/musl-1.1.18/src/prng/random.c@ 388

#include <stdlib.h>
#include <stdint.h>
#include "libc.h"

/*
this code uses the same lagged fibonacci generator as the
original bsd random implementation except for the seeding
which was broken in the original
*/

static uint32_t init[] = {
0x00000000,0x5851f42d,0xc0b18ccf,0xcbb5f646,
0xc7033129,0x30705b04,0x20fd5db4,0x9a8b7f78,
0x502959d8,0xab894868,0x6c0356a7,0x88cdb7ff,
0xb477d43f,0x70a3a52b,0xa8e4baf1,0xfd8341fc,
0x8ae16fd9,0x742d2f7a,0x0d1f0796,0x76035e09,
0x40f7702c,0x6fa72ca5,0xaaa84157,0x58a0df74,
0xc74a0364,0xae533cc4,0x04185faf,0x6de3b115,
0x0cab8628,0xf043bfa4,0x398150e9,0x37521657};

static int n = 31;
static int i = 3;
static int j = 0;
static uint32_t *x = init+1;
static volatile int lock[2];

static uint32_t lcg31(uint32_t x) {
        return (1103515245*x + 12345) & 0x7fffffff;
}

static uint64_t lcg64(uint64_t x) {
        return 6364136223846793005ull*x + 1;
}

static void *savestate() {
        x[-1] = (n<<16)|(i<<8)|j;
        return x-1;
}

static void loadstate(uint32_t *state) {
        x = state+1;
        n = x[-1]>>16;
        i = (x[-1]>>8)&0xff;
        j = x[-1]&0xff;
}

static void __srandom(unsigned seed) {
        int k;
        uint64_t s = seed;

        if (n == 0) {
                x[0] = s;
                return;
        }
        i = n == 31 || n == 7 ? 3 : 1;
        j = 0;
        for (k = 0; k < n; k++) {
                s = lcg64(s);
                x[k] = s>>32;
        }
        /* make sure x contains at least one odd number */
        x[0] |= 1;
}

void srandom(unsigned seed) {
        LOCK(lock);
        __srandom(seed);
        UNLOCK(lock);
}

char *initstate(unsigned seed, char *state, size_t size) {
        void *old;

        if (size < 8)
                return 0;
        LOCK(lock);
        old = savestate();
        if (size < 32)
                n = 0;
        else if (size < 64)
                n = 7;
        else if (size < 128)
                n = 15;
        else if (size < 256)
                n = 31;
        else
                n = 63;
        x = (uint32_t*)state + 1;
        __srandom(seed);
        savestate();
        UNLOCK(lock);
        return old;
}

char *setstate(char *state) {
        void *old;

        LOCK(lock);
        old = savestate();
        loadstate((uint32_t*)state);
        UNLOCK(lock);
        return old;
}

long random(void) {
        long k;

        LOCK(lock);
        if (n == 0) {
                k = x[0] = lcg31(x[0]);
                goto end;
        }
        x[i] += x[j];
        k = x[i]>>1;
        if (++i == n)
                i = 0;
        if (++j == n)
                j = 0;
end:
        UNLOCK(lock);
        return k;
}