drand48(3C)          COMPATIBILITY FUNCTIONS          drand48(3C)



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

SYNOPSIS
     #include <stdlib.h>

     double drand48 (void);

     double erand48 (unsigned short xsubi[3]);

     long lrand48 (void);

     long nrand48 (unsigned short xsubi[3]);

     long mrand48 (void);

     long jrand48 (unsigned short xsubi[3]);

     void srand48 (long seedval);

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

     void lcong48 (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,  one of which should be invoked before either
     drand48, lrand48, or mrand48 is called.  (Although it is not
     recommended  practice,  constant  default initializer values
     will be  supplied  automatically  if  drand48,  lrand48,  or
     mrand48  is called without a prior call to an initialization
     entry point.)  Functions erand48, nrand48,  and  jrand48  do
     not  require  an  initialization  entry  point  to be called
     first.





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drand48(3C)          COMPATIBILITY FUNCTIONS          drand48(3C)



     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 per-
     formed.   Unless  lcong48  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 by first
     generating the next 48-bit X  in  the  sequence.   Then  the
     appropriate  number  of  biti
s,  according  to  the  type  of
     data item to be returned, are  copied  from  the  high-order
     (leftmost)  bits  of  X   and  transformed into the returned
     value.                 i

     The functions drand48, lrand48, and mrand48 store  the  last
     48-bit  X  generated in an internal buffer.  X  must be ini-
     tialized i
prior to being  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 fui
nctions are invoked.  These rou-
     tines 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  diffei
rent  arguments,
     functions  erand48,  nrand48,  and  jrand48  allow  separate
     modules of a large program to generate  several  independent
     streams  of  pseudo-random  numbers,  i.e.,  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-
     orderi16 bits of X  are 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 a
iddition,
     the previous value of X  is copied into  a  48-bit  internal
     buffer, used only by see
id48, and a 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 wh
ien  the  program
     is restarted.




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drand48(3C)          COMPATIBILITY FUNCTIONS          drand48(3C)



     The initialization  function  lcong48  allows  the  user  to
     specify  the  initial  X ,  the  multiplier value a, and the
     addend value c.  Argumeni
t array elements param[0-2]  specify
     X , param[3-5] specify the multiplier a, and param[6] speci-
     fies the 16-bit 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,  speci-
     fied on the previous page.

SEE ALSO
     rand(3C).












































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