initstate(3)                                               initstate(3)

  random()

  NAME

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

  SYNOPSIS

    #include 

    long random (void)

    void srandom (unsigned seed)

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

    char * setstate (char *state)

  DESCRIPTION

    The random(3) 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 srandom(3) function has almost the same calling sequence and
    initialization properties as srand(3). The difference is that rand(3)
    produces a much less random sequence -- in fact, the low dozen bits
    generated by rand(3) rand go through a cyclic pattern. All the bits
    generated by random(3) are usable. For example,

    random()&01

    will produce a random binary value.

    Unlike srand(3), srandom(3) 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(3) will
    by default produce a sequence of numbers that can be duplicated by calling
    srandom(3) with 1 as the seed.

    The initstate(3) 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(3) 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 initstate(3) function returns a pointer to the
    previous state information array.

    Once a state has been initialized, the setstate(3) routine provides for
    rapid switching between states. The setstate(3) 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(3) or
    setstate(3).

    Once a state array has been initialized, it may be restarted at a
    different point either by calling initstate(3) (with the desired seed, the
    state array, and its size) or by calling both setstate(3) (with the state
    array) and srandom(3) (with the desired seed). The advantage of calling
    both setstate(3) and srandom(3) 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.

  RETURN VALUES

    If initstate(3) is called with less than 8 bytes of state information, or
    if setstate(3) detects that the state information has been garbled, error
    messages are printed on the standard error output.

  BUGS

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

  SEE ALSO

    rand(3)

  USAGE NOTES

    None of these functions are thread safe.

    None of these functions are async-signal safe.