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DRAND48(3P) POSIX Programmer's Manual DRAND48(3P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
delim $$
drand48, erand48, jrand48, lcong48, lrand48, mrand48, nrand48,
seed48, srand48 — generate uniformly distributed pseudo-random
numbers
#include <stdlib.h>
double drand48(void);
double erand48(unsigned short xsubi[3]);
long jrand48(unsigned short xsubi[3]);
void lcong48(unsigned short param[7]);
long lrand48(void);
long mrand48(void);
long nrand48(unsigned short xsubi[3]);
unsigned short *seed48(unsigned short seed16v[3]);
void srand48(long seedval);
This family of functions shall generate pseudo-random numbers using a
linear congruential algorithm and 48-bit integer arithmetic.
The drand48() and erand48() functions shall return non-negative,
double-precision, floating-point values, uniformly distributed over
the interval [0.0,1.0).
The lrand48() and nrand48() functions shall return non-negative, long
integers, uniformly distributed over the interval [0,231).
The mrand48() and jrand48() functions shall return signed long
integers uniformly distributed over the interval [−231,231).
The srand48(), seed48(), and lcong48() functions 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 shall be supplied
automatically if drand48(), lrand48(), or mrand48() is called without
a prior call to an initialization entry point.) The erand48(),
nrand48(), and jrand48() functions do not require an initialization
entry point to be called first.
All the routines work by generating a sequence of 48-bit integer
values, $X_ i" " ,$ according to the linear congruential formula:
$X sub{n+1} " " = " " (aX_ n" "^+^c) sub{roman mod " " m} " "
" " " " " " " " " " " " " " n>= " " 0$
The parameter $m^=^2"^" 48$; hence 48-bit integer arithmetic is
performed. Unless lcong48() is invoked, the multiplier value $a$ and
the addend value $c$ are given by:
$a " " mark = " " roman "5DEECE66D"^sub 16 " " = " " roman
273673163155^sub 8$
$c " " lineup = " " roman B^sub 16 " " = " " roman 13^sub 8$
The value returned by any of the drand48(), erand48(), jrand48(),
lrand48(), mrand48(), or nrand48() functions is computed by first
generating the next 48-bit $X_ i$ in the sequence. Then the
appropriate number of bits, according to the type of data item to be
returned, are copied from the high-order (leftmost) bits of $X_ i$
and transformed into the returned value.
The drand48(), lrand48(), and mrand48() functions store the last
48-bit $X_ i$ generated in an internal buffer; that is why the
application shall ensure that these are initialized prior to being
invoked. The erand48(), nrand48(), and jrand48() functions require
the calling program to provide storage for the successive $X_ i$
values in the array specified as an argument when the functions are
invoked. That is why these routines do not have to be initialized;
the calling program merely has to place the desired initial value of
$X_ i$ into the array and pass it as an argument. By using different
arguments, 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 shall
not depend upon how many times the routines are called to generate
numbers for the other streams.
The initializer function srand48() sets the high-order 32 bits of $X_
i$ to the low-order 32 bits contained in its argument. The low-order
16 bits of $X_ i$ are set to the arbitrary value $roman 330E_ 16" "
.$
The initializer function seed48() sets the value of $X_ i$ to the
48-bit value specified in the argument array. The low-order 16 bits
of $X_ i$ are set to the low-order 16 bits of seed16v[0]. The mid-
order 16 bits of $X_ i$ are set to the low-order 16 bits of
seed16v[1]. The high-order 16 bits of $X_ i$ are set to the low-
order 16 bits of seed16v[2]. In addition, the previous value of $X_
i$ is copied into a 48-bit internal buffer, used only by seed48(),
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 $X_ i$ value, and
then use this value to reinitialize via seed48() when the program is
restarted.
The initializer function lcong48() allows the user to specify the
initial $X_ i" " ,$ the multiplier value $a,$ and the addend value
$c.$ Argument array elements param[0-2] specify $X_ i" " ,$
param[3-5] specify the multiplier $a,$ and param[6] specifies the
16-bit addend $c.$ After lcong48() is called, a subsequent call to
either srand48() or seed48() shall restore the standard multiplier
and addend values, a and c, specified above.
The drand48(), lrand48(), and mrand48() functions need not be thread-
safe.
As described in the DESCRIPTION above.
No errors are defined.
The following sections are informative.
None.
None.
None.
None.
rand(3p)
The Base Definitions volume of POSIX.1‐2008, stdlib.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 DRAND48(3P)
Pages that refer to this page: stdlib.h(0p), erand48(3p), initstate(3p), jrand48(3p), lcong48(3p), lrand48(3p), mrand48(3p), nrand48(3p), rand(3p), seed48(3p), srand48(3p)