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man:drand48

DRAND48(3) Linux Programmer's Manual DRAND48(3)

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 int lrand48(void);
     long int nrand48(unsigned short xsubi[3]);
     long int mrand48(void);
     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]);
 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
     All functions shown above: _XOPEN_SOURCE
         || /* Glibc since 2.19: */ _DEFAULT_SOURCE
         || /* Glibc versions <= 2.19: */ _SVID_SOURCE

DESCRIPTION

     These functions generate pseudo-random numbers using the linear congru-
     ential algorithm and 48-bit integer arithmetic.
     The  drand48() and erand48() functions return nonnegative double-preci-
     sion floating-point values  uniformly  distributed  over  the  interval
     [0.0, 1.0).
     The  lrand48() and nrand48() functions return nonnegative long integers
     uniformly distributed over the interval [0, 2^31).
     The mrand48() and jrand48() functions return signed long integers  uni-
     formly distributed over the interval [-2^31, 2^31).
     The  srand48(),  seed48()  and  lcong48()  functions are initialization
     functions, one of  which  should  be  called  before  using  drand48(),
     lrand48()   or  mrand48().   The  functions  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 formula:
         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  gen-
     erating  the next 48-bit Xi in the sequence.  Then the appropriate num-
     ber 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 functions erand48(), nrand48()
     and jrand48() require the calling program to provide  storage  for  the
     successive  Xi  values  in the array argument xsubi.  The functions are
     initialized 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  ini-
     tial  values for Xi, a and c.  Array argument elements param[0-2] spec-
     ify  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.

ATTRIBUTES

     For  an  explanation  of  the  terms  used   in   this   section,   see
     attributes(7).
     +----------------------+---------------+------------------------+
     |Interface             | Attribute     | Value                  |
     +----------------------+---------------+------------------------+
     |drand48(), erand48(), | Thread safety | MT-Unsafe race:drand48 |
     |lrand48(), nrand48(), |               |                        |
     |mrand48(), jrand48(), |               |                        |
     |srand48(), seed48(),  |               |                        |
     |lcong48()             |               |                        |
     +----------------------+---------------+------------------------+
     The above functions record global state information for the random num-
     ber generator, so they are not thread-safe.

CONFORMING TO

     POSIX.1-2001, POSIX.1-2008, SVr4.

SEE ALSO

     rand(3), random(3)

COLOPHON

     This  page  is  part of release 4.16 of the Linux man-pages project.  A
     description of the project, information about reporting bugs,  and  the
     latest     version     of     this    page,    can    be    found    at
     https://www.kernel.org/doc/man-pages/.
                                2017-09-15                        DRAND48(3)
/data/webs/external/dokuwiki/data/pages/man/drand48.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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