rand.c File Reference

#include <stdlib.h>

Include dependency graph for rand.c:

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Functions
static int	do_rand (unsigned long *ctx)
	__attribute__ ((weak))

Variables
static unsigned long	next = 1

Function Documentation

__attribute__()

__attribute__

(

(weak)

)

Definition at line 71 of file rand.c.

{
    unsigned long val = (unsigned long)*ctx;
    int r = do_rand(&val);

    *ctx = (unsigned int)val;
    return (r);
}

References do_rand().

do_rand()

static int do_rand ( unsigned long *  ctx )

static

Definition at line 35 of file rand.c.

{
#ifdef USE_WEAK_SEEDING
    /*
     * Historic implementation compatibility.
     * The random sequences do not vary much with the seed,
     * even with overflowing.
     */
    return ((*ctx = *ctx * 1103515245 + 12345) % ((unsigned long)RAND_MAX + 1));
#else /* !USE_WEAK_SEEDING */
    /*
     * Compute x = (7^5 * x) mod (2^31 - 1)
     * without overflowing 31 bits:
     *      (2^31 - 1) = 127773 * (7^5) + 2836
     * From "Random number generators: good ones are hard to find",
     * Park and Miller, Communications of the ACM, vol. 31, no. 10,
     * October 1988, p. 1195.
     */
    long hi, lo, x;

    /* Can't be initialized with 0, so use another value. */
    if(*ctx == 0)
    {
        *ctx = 123459876;
    }
    hi = *ctx / 127773;
    lo = *ctx % 127773;
    x = 16807 * lo - 2836 * hi;
    if(x < 0)
    {
        x += 0x7fffffff;
    }
    return (int)((*ctx = (unsigned long)x) % ((unsigned long)RAND_MAX + 1));
#endif /* !USE_WEAK_SEEDING */
}

References RAND_MAX.

Referenced by __attribute__().

Variable Documentation

next

unsigned long next = 1

static

Definition at line 34 of file rand.c.