DRAND48(8)          Linux Programmer's Manual          DRAND48(8)



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

SYNOPSIS
       #include <stdlib.h>

       double drand48(8);

       double erand48(unsigned short xsubi[3]);

       long int lrand48(8);

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

       long int mrand48(8);

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

       void srand48(long int seedval);

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

       void lcong48(unsigned short param[7]);

DESCRIPTION
       These  functions  generate pseudo-random numbers using the
       linear congruential algorithm and  48-bit  integer  arith-
       metic.

       The  drand48() and erand48() functions return non-negative
       double-precision  floating-point  values  uniformly   dis-
       tributed between [0.0, 1.0).

       The  lrand48() and nrand48() functions return non-negative
       long integers uniformly distributed between 0 and 2^31.

       The mrand48() and jrand48() functions return  signed  long
       integers uniformly distributed between -2^31 and 2^31.

       The  srand48(),  seed48() and lcong48() functions are ini-
       tialization functions,  one  of  which  should  be  called
       before using drand48(), lrand48() or mrand48().  The func-
       tions erand48(), nrand48() and jrand48() do not require an
       initialization function to be called first.

       All  the functions work by generating a sequence of 48-bit
       integers, Xi, according to the  linear  congruential  for-
       mula:

              Xn+1 = (aXn + c) mod m, where n >= 0

       The parameter m = 2^48, hence 48-bit integer arithmetic is
       performed.  Unless lcong48() is called, a and c are  given
       by:

              a = 0x5DEECE66D
              c = 0xB

       The  value  returned  by  any  of the functions drand48(),
       erand48(), lrand48(), nrand48(), mrand48() or jrand48() is
       computed  by  first  generating  the next 48-bit Xi in the
       sequence.  Then the appropriate number of bits,  according
       to  the  type  of data item to be returned, is copied from
       the  high-order  bits  of  Xi  and  transformed  into  the
       returned value.

       The functions drand48(), lrand48() and mrand48() store the
       last 48-bit Xi generated in an internal buffer.  The func-
       tions erand48(), nrand48() and jrand48() require the call-
       ing program to provide storage for the successive Xi  val-
       ues  in  the array argument xsubi.  The functions are ini-
       tialized by placing the initial value of Xi into the array
       before calling the function for the first time.

       The  initializer  function  srand48()  sets the high order
       32-bits of Xi to the  argument  seedval.   The  low  order
       16-bits are set to the arbitrary value 0x330E.

       The  initializer function seed48() sets the value of Xi to
       the 48-bit value specified in the array argument  seed16v.
       The previous value of Xi is copied into an internal buffer
       and a pointer to this buffer is returned by seed48().

       The initialization function lcong48() allows the  user  to
       specify  initial  values  for Xi, a and c.  Array argument
       elements param[0-2] specify Xi, param[3-5] specify a,  and
       param[6]  specifies c.  After lcong48() has been called, a
       subsequent call  to  either  srand48()  or  seed48()  will
       restore the standard values of a and c.

CONFORMING TO
       SVID 3

NOTES
       These  functions  are  declared  obsolete by SVID 3, which
       states that rand(d) should be used instead.

SEE ALSO
       rand(d), random(m)



                            1993-07-02                 DRAND48(8)