c - Rand Implementation

Question

I would like to go through how rand() and srand() functions are implemented and would like to tweak the code to modify it to my requirements. Where can i find the source code of rand() and srand().

Answer 1

rand and srand are usually implemented as a simple LCG, you can easily write your own (it's few lines of code) without looking for the sources of rand and srand. Notice that, if you need random numbers for "serious" purposes (e.g. cryptography), there are much better RNGs than LCG.

By the way, the C standard itself includes a sample implementation of rand and srand:

static unsigned long int next = 1;

int rand(void) // RAND_MAX assumed to be 32767
{
    next = next * 1103515245 + 12345;
    return (unsigned int)(next/65536) % 32768;
}

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