DRAND48(3C)                          SysV                          DRAND48(3C)



NAME
     drand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48, seed48,
     lcong48 - generate uniformly distributed pseudo-random numbers

SYNOPSIS
     # include <stdlib.h>
     double drand48 ( )

     double erand48 (xsubi)
     unsigned short xsubi[3];

     long lrand48 ( )

     long nrand48 (xsubi)
     unsigned short xsubi[3];

     long mrand48 ( )

     long jrand48 (xsubi)
     unsigned short xsubi[3];

     void srand48 (seedval)
     long seedval;

     unsigned short *seed48 (seed16v)
     unsigned short seed16v[3];

     void lcong48 (param)
     unsigned short param[7];

DESCRIPTION
     This family of functions generates pseudo-random numbers using the well-
     known linear congruential algorithm and 48-bit integer arithmetic.

     Functions drand48 and erand48 return non-negative double-precision
     floating-point values uniformly distributed over the interval [0.0, 1.0).

     Functions lrand48 and nrand48 return non-negative long integers uniformly
     distributed over the interval [0, 231).

     Functions mrand48 and jrand48 return signed long integers uniformly
     distributed over the interval [-231, 231).

     Functions srand48, seed48 and lcong48 are initialization entry points.
     You should invoke one of these before invoking either drand48, lrand48 or
     mrand48.  (Constant default initializer values will be supplied
     automatically if you call drand48, lrand48 or mrand48 without calling an
     initialization entry point first.  However, we recommend that you make a
     call to an initialization entry point.)  Functions erand48, nrand48, and
     jrand48 do not require an initialization entry point to be called first.

     All the routines work by generating a sequence of 48-bit integer values,
     X , according to the linear congruential formula
      i
                          X    = (aX +c)             n>0.
                           n+1      n   mod m
     The parameter m=248; hence 48-bit integer arithmetic is performed.
     Unless lcong4b has been invoked, the multiplier value a and the addend
     value c are given by

           a = 5DEECE66D   = 273673163155

           c = B   = 13 16               8
                16     8
     The value returned by any of the functions drand48, erand48, lrand48,
     nrand48, mrand48, or jrand48 is computed in the following fashion.
     First, the function  generates the next 48-bit X  in the sequence.  Then
     it copies the appropriate number of bits, according to the type of data
     item to be returned, from the high-order (leftmost) bits of X  and
     transforms them into the returned value.                     i

     The functions drand48, lrand48, and mrand48 store the last 48-bit X
     generated in an internal buffer, and must be initialized prior to biing
     invoked.  The functions erand48, nrand48 and jrand48 require the calling
     program to provide storage for the successive X  values in the array
     specified as an argument when the functions areiinvoked.  These routines
     do not have to be initialized; the calling program must place the desired
     initial value of X  into the array and pass it as an argument.  By using
     different argumenti, functions erand48, nrand48, and jrand48 allow
     separate modules of a large program to generate several independent
     streams of pseudo-random numbers, that is, the sequence of numbers in
     each stream will not depend upon how many times the routines have been
     called to generate numbers for the other streams.

     The initializer function srand48 sets the high-order 32 bits of X  to the
     32 bits contained in its argument.  The low-order 16 bits of X  aie set
     to the arbitrary value 330E  .                                i
                                16
     The initializer function seed48 sets the value of X  to the 48-bit value
     specified in the argument array.  In addition, the irevious value of X
     is copied into a 48-bit internal buffer, used only by seed48, and a   i
     pointer to this buffer is the value returned by seed48.  This returned
     pointer, which can just be ignored if not needed, is useful if a program
     is to be restarted from a given point at some future time - use the
     pointer to get at and store the last X  value, and then use this value to
     reinitialize via seed48 when the progrim is restarted.

     The initialization function lcong48 allows the user to specify the
     initial X , the multiplier value a, and the addend value c.  Argument
     array eleients param[0-2] specify X , param[3-5] specify the multiplier
     a, and param[6] specifies the 16-bii addend c.  After lcong48 has been
     called, a subsequent call to either srand48 or seed48 will restore the
     "standard" multiplier and addend values, a and c, specified on the
     previous page.

NOTES
     The source code for the portable version can be used on computers which
     do not have floating-point arithmetic.  In such a situation, functions
     drand48 and erand48 are replaced by the two new functions below.

     long irand48 (m)
     unsigned short m;

     long krand48 (xsubi, m)
     unsigned short xsubi[3], m;

     Functions irand48 and krand48 return non-negative long integers uniformly
     distributed over the interval [0, m-1].

SEE ALSO
     rand(3C).