setstate(3m) [hpux man page]

random(3M)																random(3M)

NAME

       random(), srandom(), initstate(), setstate() - generate a pseudorandom number

SYNOPSIS

DESCRIPTION

       The and functions are random-number generators that have virtually the same calling sequence and initialization properties as the and func-
       tions, but produce sequences that are more random.  The low 12 bits generated by the function go through a cyclic pattern,  while  all  the
       bits generated by the function are usable.  For example, produces a random binary value.

       The  function uses a nonlinear additive feedback random-number generator employing a default state array size of 31 long integers to return
       successive pseudorandom numbers in the range from 0 to The period of this random-number generator is approximately 16 x	The  size  of  the
       state array determines the period of the random-number generator.  Increasing the state array size increases the period.

       With 256 bytes of state information, the period of the random-number generator is greater than

       Like  the function, the function produces by default a sequence of numbers that can be duplicated by calling the function with a value of 1
       as the seed.

       The function initializes the current state array using the value of seed.

       The and functions handle restarting and changing random-number generators.  The function allows a state array,  pointed	to  by	the  state
       argument,  to be initialized for future use.  The size argument, which specifies the size in bytes of the state array, is used by the func-
       tion to decide how sophisticated a random-number generator to use; the larger the state array, the more random the numbers.  Values for the
       amount  of  state  information are 8, 32, 64, 128, and 256 bytes.  Amounts less than 8 bytes return a NULL pointer, while other amounts are
       rounded down to the nearest known value.  The seed argument specifies a starting point for the  random-number  sequence	and  provides  for
       restarting at the same point.  The function returns a pointer to the previous state information array.

       Once a state has been initialized, the function allows switching between state arrays.  The array defined by the state argument is used for
       further random-number generation until the function is called or the function is called again.  The function returns a pointer to the  pre-
       vious state array.

       After initialization, a state array can be restarted at a different point in one of two ways:

	      The function can be used, with the desired seed, state array, and size of the array.

	      The  function,  with the desired state, can be used, followed by the function with the desired seed.  The advantage of using both of
	      these functions is that the size of the state array does not have to be saved once it is initialized.

RETURN VALUE

       The function returns the generated pseudorandom number.

       The function returns no value.

       Upon successful completion, the and functions return a pointer to the previous state array.  Otherwise, a NULL pointer is returned.

ERRORS

       If the function detects that the state information has been damaged, error messages are written to standard error.

SEE ALSO

       drand48(3C), rand(3C), random(7).

STANDARDS CONFORMANCE

																	random(3M)

RANDOM(3)						     Library Functions Manual							 RANDOM(3)

NAME

       random, srandom, initstate, setstate - better random number generator; routines for changing generators

SYNOPSIS

       long random()

       srandom(seed)
       int seed;

       char *initstate(seed, state, n)
       unsigned seed;
       char *state;
       int n;

       char *setstate(state)
       char *state;

DESCRIPTION

       Random  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).

       Random/srandom  have  (almost)  the same calling sequence and initialization properties as rand/srand.  The difference is that rand(3) pro-
       duces a much less random sequence -- in fact, the low dozen bits generated by rand go through a cyclic pattern.	All the bits generated	by
       random are usable.  For example, ``random()&01'' will produce a random binary value.

       Unlike  srand,  srandom	does not return the old seed; the reason for this is that the amount of state information used is much more than a
       single word.  (Two other routines are provided to deal with restarting/changing random number generators).  Like rand(3),  however,  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.  Initstate returns a
       pointer to the previous state information array.

       Once a state has been initialized, the setstate routine provides for rapid switching between states.  Setstate 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  call-
       ing 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.

AUTHOR

       Earl T. Cohen

DIAGNOSTICS

       If 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.

SEE ALSO

       rand(3)

BUGS

       About 2/3 the speed of rand(3C).

4.2 Berkeley Distribution					September 29, 1985							 RANDOM(3)