initstate man page on Ultrix

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random(3)							     random(3)

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

Syntax
       long random()

       void srandom(seed)
       int seed;

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

       char *setstate(state)
       char *state;

Description
       The subroutine uses a non-linear additive feedback random number gener‐
       ator  employing a default table of size 31 long integers to return suc‐
       cessive 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 subroutines have (almost) the same calling sequence and initializa‐
       tion  properties as The difference is that rand(3) produces a much less
       random sequence - in fact, the low dozen	 bits  generated  by  rand  go
       through	a  cyclic pattern.  All the bits generated by are usable.  For
       example, “random()&01” will produce a random binary value.

       Unlike 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 however, will by default produce a sequence
       of numbers that can be duplicated by calling with 1 as the seed.

       The routine allows a state array, passed in as an argument, to be  ini‐
       tialized	 for  future  use.   The size of the state array (in bytes) is
       used by 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.   returns	a  pointer  to	the previous state information
       array.

       Once a state has been  initialized,  the	 routine  provides  for	 rapid
       switching between states.  The subroutine returns a pointer to the pre‐
       vious state array; its argument state array is used for further	random
       number generation until the next call to or

       Once  a state array has been initialized, it may be restarted at a dif‐
       ferent point either by calling (with the desired seed, the state array,
       and  its	 size) or by calling both (with the state array) and (with the
       desired seed).  The advantage of calling both and 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 269, which should be sufficient for most pur‐
       poses.

Diagnostics
       If is called with less than 8 bytes of state information, or if detects
       that the state information has been garbled, error messages are printed
       on the standard error output.

See Also
       rand(3)

								     random(3)
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