How to get a larger random number from the c function rand()

Question

I am in a coding environment where I only have access to some most basic c functions. #include\'ing other lib is not feasible.

In this environment, I can call rand()

Answer 1

static unsigned long next = 1;
int my_rand(void) {
    next = next * 1103515245 + 12345;
    return((unsigned)(next/65536) % (RAND_MAX+1));
}

void my_srand(unsigned int seed) {
    next = seed;
}

on linux

#define RAND_MAX    2147483647

your environment RAND_MAX is probably 32767

reference: http://en.wikipedia.org/wiki/Linear_congruential_generator

if you are not memory constrained you can look also at http://en.wikipedia.org/wiki/Mersenne_twister the code is embeddable as like as the example above