Manual Pages for UNIX Operating System command usage for man setstate

Standard C Library Functions                           random(3C)



NAME
     random, srandom, initstate, setstate -  pseudorandom  number
     functions

SYNOPSIS
     #include 

     long random(void);


     void srandom(unsigned int seed);


     char *initstate(unsigned int seed, char *state, size_t size);


     char *setstate(const char *state);


DESCRIPTION
     The random() function uses  a  nonlinear  additive  feedback
     random-number generator employing a default state array size
     of 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 approximately 16 x (2^31 -1). The
     size  of  the  state  array  determines  the  period  of the
     random-number generator. Increasing  the  state  array  size
     increases the period.


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


     The random() and srandom() functions have (almost) the  same
     calling sequence and initialization properties as rand() and
     srand() (see rand(3C)). The difference is that rand(3C) 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.


     The algorithm from rand() is used by srandom()  to  generate
     the  31 state integers. Because of this, different srandom()
     seeds often produce, within an offset, the same sequence  of
     low  order  bits  from  random(). If low order bits are used
     directly, random() should  be  initialized  with  setstate()
     using high quality random values.


     Unlike srand(), srandom()  does  not  return  the  old  seed
     because  the  amount  of state information used is much more



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Standard C Library Functions                           random(3C)



     than a single word. Two other routines are provided to  deal
     with  restarting/changing random number generators. 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.


     Like rand(3C), random() produces by default  a  sequence  of
     numbers  that  can be duplicated by calling srandom() with 1
     as the seed.


     The initstate() and setstate() functions  handle  restarting
     and  changing  random-number  generators.   The  initstate()
     function allows a state array, pointed to by the state argu-
     ment,  to  be initialized for future use. The size argument,
     which specifies the size in bytes of  the  state  array,  is
     used  by  initstate()  to  decide what type of random-number
     generator to use; the larger the state array, the more  ran-
     dom the numbers.  Values for the amount of state information
     are 8, 32, 64, 128, and 256  bytes.   Other  values  greater
     than  8  bytes  are rounded down to the nearest one of these
     values.  For values smaller than 8, random() uses  a  simple
     linear congruential random number generator.  The seed argu-
     ment  specifies  a  starting  point  for  the  random-number
     sequence and provides for restarting at the same point.  The
     initstate() function returns a pointer to the previous state
     information array.


     If initstate() has not been called, then random() behaves as
     though initstate() had been called with seed=1 and size=128.


     If initstate() is called with size<8, then random()  uses  a
     simple linear congruential random number generator.


     Once a state has been initialized, setstate() allows switch-
     ing  between  state  arrays.  The array defined by the state
     argument is used for further random-number generation  until
     initstate()  is  called  or  setstate() is called again. The
     setstate() function returns a pointer to the previous  state
     array.

RETURN VALUES
     The random() function returns  the  generated  pseudo-random
     number.


     The srandom() function returns no value.




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Standard C Library Functions                           random(3C)



     Upon  successful  completion,  initstate()  and   setstate()
     return  a pointer to the previous state array.  Otherwise, a
     null pointer is returned.

ERRORS
     No errors are defined.

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

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

         o    The setstate() function, with  the  desired  state,
              can be used, followed by srandom() with the desired
              seed. The advantage of using both  of  these  func-
              tions  is that the size of the state array does not
              have to be saved once it is initialized.

EXAMPLES
     Example 1 Initialize an array.


     The following example demonstrates the use of initstate() to
     intialize  an  array. It also demonstrates how to initialize
     an array and pass it to setstate().


       # include 
       static unsigned int state0[32];
       static unsigned int state1[32] = {
            3,
            0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342,
            0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
            0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86,
            0xda672e2a, 0x1588ca88, 0xe369735d, 0x904f35f7,
            0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
            0xde3b81e0, 0xdf0a6fb5, 0xf103bc02, 0x48f340fb,
            0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b,
            0xf5ad9d0e, 0x8999220b, 0x27fb47b9
            };
       main() {
            unsigned seed;
            int n;
            seed = 1;
            n = 128;
            (void)initstate(seed, (char *)state0, n);
            printf("random() = %d0\n", random());
            (void)setstate((char *)state1);
            printf("random() = %d0\n", random());
       }



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Standard C Library Functions                           random(3C)



ATTRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:



     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Interface Stability         | Committed                   |
    |_____________________________|_____________________________|
    | MT-Level                    | See NOTES below.            |
    |_____________________________|_____________________________|
    | Standard                    | See standards(5).           |
    |_____________________________|_____________________________|


SEE ALSO
     drand48(3C), rand(3C), attributes(5), standards(5)

NOTES
     The random() and srandom()  functions  are  unsafe  in  mul-
     tithreaded applications.


     Use of these  functions  in  multithreaded  applications  is
     unsupported.


     For initstate() and setstate(), the state argument  must  be
     aligned on an int boundary.


     Newer and better performing random number generators such as
     addrans() and lcrans() are available with the SUNWspro pack-
     age.



















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