генерировать равномерно распределенные псевдослучайные числа (generate uniformly distributed pseudo-random numbers)
Имя (Name)
drand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48,
seed48, lcong48 - generate uniformly distributed pseudo-random
numbers
Синопсис (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]);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
All functions shown above:
_XOPEN_SOURCE
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc <= 2.19: */ _SVID_SOURCE
Описание (Description)
These functions generate pseudo-random numbers using the linear
congruential algorithm and 48-bit integer arithmetic.
The drand48() and erand48() functions return nonnegative double-
precision 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
uniformly 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 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 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
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.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────────────┬───────────────┬──────────────┐
│Interface │ Attribute │ Value │
├─────────────────────────────────┼───────────────┼──────────────┤
│drand48(), erand48(), lrand48(), │ Thread safety │ MT-Unsafe │
│nrand48(), mrand48(), jrand48(), │ │ race:drand48 │
│srand48(), seed48(), lcong48() │ │ │
└─────────────────────────────────┴───────────────┴──────────────┘
The above functions record global state information for the
random number generator, so they are not thread-safe.
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008, SVr4.
Смотри также (See also)
rand(3), random(3)
