about rand

[xcm]

#include <stdlib.h>

static unsigned long int next = 1;

int rand(void)
{
next = next * 1103515245 + 12345;
return (unsigned int)(next/(2 * (RAND_MAX +1L)) % (RAND_MAX+1L));
}

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




next = next * 1103515245 + 12345;


1103515245,12345
why not 1103511234 ,54321?

 

[A. Sinan Unur]

#include <stdlib.h>

static unsigned long int next = 1;

int rand(void)
{
next = next * 1103515245 + 12345;
return (unsigned int)(next/(2 * (RAND_MAX +1L)) % (RAND_MAX+1L));
}

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

rand and srand are functions provided by the standard library. Why are
you re-writing them?

next = next * 1103515245 + 12345;


1103515245,12345
why not 1103511234 ,54321?

What do you mean?

 

[Peter Nilsson]

xcm wrote:

next = next * 1103515245 + 12345;

1103515245,12345
why not 1103511234 ,54321?

Well, why not 42 and 27?

Do some googling on PRNG and linear congruential generators.

Your question doesn't seem to be about C specifically, rather it
seems to be about a particular algorithm used to implement one
version of rand(). But the C standards don't require a specific
algorithm for rand(), and comp.lan.c is not an algorithms group.