srand48

Initializes a 48-bit random number generator.

Format

#include  <stdlib.h>

void srand48  (long int seed_val);

Arguments

seed_val

The initialization value to begin randomization. Changing this value changes the randomization pattern.

Description

This function initializes the random number generator. You can use this function in your program before calling the drand48, lrand48, or mrand48 functions. (Although it is not recommended practice, constant default initializer values are supplied automatically if you call drand48, lrand48, or mrand48 without calling an initialization function).

The function works by generating a sequence of 48-bit integer values, Xi, according to the linear congruential formula:

       Xn+1 = (aXn+c)mod m        n >= 0

The argument m equals 248 , so 48-bit integer arithmetic is performed. Unless you invoke the lcong48 function, the multiplier value a and the addend value c are:

      a = 5DEECE66D16 = 2736731631558

      c = B16 = 138

The initializer function srand48 sets the high-order 32 bits of Xi to the low-order 32 bits contained in its argument. The low-order 16 bits of Xi are set to the arbitrary value 330E 16 .

See also drand48, lrand48, and mrand48 in this section.