drand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48, seed48, lcong48 - generate uniformly distributed pseudo-random numbers
#include <stdlib.h> double drand48(void); double erand48(unsigned short xsubi); long lrand48(void); long nrand48(unsigned short xsubi); long mrand48(void); long jrand48(unsigned short xsubi); void srand48(long seedval); unsigned short *seed48(unsigned short seed16v); void lcong48(unsigned short param);
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
These functions generate pseudo-random numbers using the linear congruential algorithm and 48-bit integer arithmetic.
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
m = 2^48, hence 48-bit integer arithmetic is
performed. Unless lcong48() is called,
c are given by:
a = 0x5DEECE66D c = 0xB
The value returned by any of the functions
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
transformed into the returned value.
The functions drand48(), lrand48(),
and mrand48() store the last 48-bit
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
Xi into the array before calling the function for the
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
The initialization function lcong48() allows the
user to specify initial values for
c. Array argument elements
c. After lcong48()
has been called, a subsequent call to either srand48()
or seed48() will restore the standard values of
For an explanation of the terms used in this section, see attributes(7).
|drand48(), erand48(), lrand48(), nrand48(), mrand48(), jrand48(), srand48(), seed48(), lcong48()||Thread safety||MT-Unsafe race:drand48|
The above functions record global state information for the random number generator, so they are not thread-safe.
POSIX.1-2001, POSIX.1-2008, SVr4.
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