| RANDOM(3) | Library Functions Manual | RANDOM(3) | 
random, srandom,
  initstate, setstate —
#include <stdlib.h>
long
  
  random(void);
void
  
  srandom(unsigned
    int seed);
char *
  
  initstate(unsigned
    int seed, char
    *state, size_t
  n);
char *
  
  setstate(char
    *state);
random() function uses a non-linear additive
  feedback random number generator employing a default table of size 31 long
  integers to return successive pseudo-random numbers in the range from 0 to
  (2**31)−1. The period of this random number generator is very large,
  approximately 16*((2**31)−1). The maximum value
  RANDOM_MAX is defined in
  <stdlib.h>.
The random() and
    srandom() have (almost) the same calling sequence
    and initialization properties as
    rand(3) and
    srand(3). The difference is
    that rand(3) produces a much
    less random sequence — in fact, the low dozen bits generated by
    rand(3) go through a cyclic
    pattern. All the bits generated by random() are
    usable. For example, ‘random()&01’
    will produce a random binary value.
Like rand(3),
    random() will by default produce a sequence of
    numbers that can be duplicated by calling srandom()
    with ‘1’ as the seed.
The initstate() routine allows a state
    array, passed in as an argument, to be initialized for future use. The size
    of the state array (in bytes) is used by initstate()
    to decide how sophisticated a random number generator it should use —
    the more state, the better the random numbers will be. (Current
    "optimal" values for the amount of state information are 8, 32,
    64, 128, and 256 bytes; other amounts will be rounded down to the nearest
    known amount. Using less than 8 bytes will cause an error). The seed for the
    initialization (which specifies a starting point for the random number
    sequence, and provides for restarting at the same point) is also an
    argument. The state array passed to initstate() must
    be aligned to a 32-bit boundary. This can be achieved by using a
    suitably-sized array of ints, and casting the array to char * when passing
    it to initstate(). The
    initstate() function returns a pointer to the
    previous state information array.
Once a state has been initialized, the
    setstate() routine provides for rapid switching
    between states. The setstate() function returns a
    pointer to the previous state array; its argument state array is used for
    further random number generation until the next call to
    initstate() or
  setstate().
Once a state array has been initialized, it may be restarted at a
    different point either by calling initstate() (with
    the desired seed, the state array, and its size) or by calling both
    setstate() (with the state array) and
    srandom() (with the desired seed). The advantage of
    calling both setstate() and
    srandom() is that the size of the state array does
    not have to be remembered after it is initialized.
With 256 bytes of state information, the period of the random number generator is greater than 2**69 which should be sufficient for most purposes.
initstate() is called with less than 8 bytes of state
  information, or if setstate() detects that the state
  information has been garbled, error messages are printed on the standard error
  output.
random(), srandom(),
  initstate() and setstate()
  functions conform to IEEE Std 1003.1-2008
  (“POSIX.1”).
| June 12, 2014 | NetBSD 9.3 |