drand48, drand48_r, erand48, erand48_r, jrand48,
jrand48_r, lcong48, lcong48_r, lrand48, lrand48_r,
mrand48, mrand48_r, nrand48, nrand48_r, seed48, seed48_r,
srand48, srand48_r - Generate uniformly distributed pseudorandom
number sequences
#include <stdlib.h>
double drand48(
void ); int drand48_r(
struct drand48_data *dp,
double *randval ); double erand48(
unsigned short xsubi[3] ); int erand48_r(
unsigned short xsubi[3],
struct drand48_data *dp,
double *randval ); long jrand48(
unsigned short xsubi[3] ); int jrand48_r(
unsigned short xsubi[3],
struct drand48_data *dp,
double *randval ); void lcong48(
unsigned short param[7] ); int lcong48_r(
unsigned short param[7],
struct drand48_data *dp ); long lrand48(
void ); int lrand48_r(
struct drand48_data *dp,
long *randval ); long mrand48(
void ); int mrand48_r(
struct drand48_data *dp,
long *randval ); long nrand48(
unsigned short xsubi[3] ); long nrand48_r(
unsigned short xsubi[3],
struct drand48_data *dp,
long *randval ); unsigned short *seed48(
unsigned short seed_16v[3] ); int *seed48_r(
unsigned short seed_16v[3],
struct drand48_data *dp ); void srand48(
long seed_val ); int srand48_r(
long seed_val,
struct drand48_data *dp );
Standard C Library (libc)
Interfaces documented on this reference page conform to
industry standards as follows:
drand48(), erand48(), jrand48(), lcong48(), lrand48(),
mrand48(), nrand48(), seed48(), srand48(): XPG4,
XPG4-UNIX
drand48_r(), erand48_r(), jrand48_r(), lcong48_r(),
lrand48_r(), mrand48_r(), nrand48_r(), seed48_r(),
srand48_r(): POSIX.1c
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Specifies an array of three shorts, which, when concatenated
together, form a 48-bit integer. Specifies the initialization
value to begin randomization. Changing this
value changes the randomization pattern. Specifies
another seed value; an array of three unsigned shorts that
form a 48-bit seed value. Specifies an array that in turn
specifies the initial X[i], the multiplier value a, and
the addend value c. [POSIX] Points to a structure which
contains data for the reentrant routines. [POSIX] Points
at the returned nonnegative pseudorandom numbers.
This family of functions generates pseudorandom 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 range of y values such that 0<=y < 1.0.
The lrand48() and nrand48() functions return nonnegative
long integers uniformly distributed over the range of y
values such that 0 <= y < 2^31.
The mrand48() and jrand48() functions return signed long
integers uniformly distributed over the range of y values
such that -2^31<= y < 2^31.
The srand48(), seed48(), and lcong48() functions initialize
the random-number generator. Programs should invoke
one of them before calling the drand48(), lrand48(), or
the mrand48() functions. (Although it is not recommended
practice, constant default initializer values are supplied
automatically if the drand48(), lrand48(), or mrand48()
functions are called without first calling an initialization
function.) The erand48(), nrand48(), and jrand48()
functions do not require that an initialization function
be called first.
All the functions work by generating a sequence of 48-bit
integer values, X[i], according to the linear congruential
formula:
X[n + 1] = (aX[n] + c)[mod m] n>= 0
The parameter m equals 2^48 hence 48-bit integer arithmetic
is performed. Unless lcong48() has been invoked, the
multiplier value a() and the addend value c are given by
a = 5DEECE66D (hex) = 273673163155 (octal)
c = B (hex) = 13 (octal)
The values returned by the drand48(), erand48(),
lrand48(), nrand48(), mrand48(), and jrand48() functions
are computed by first generating the next 48-bit X[i] in
the sequence. Then the appropriate bits, according to the
type of data item to be returned, are copied from the
high-order (most-significant) bits of X[i] and transformed
into the returned value.
The drand48(), lrand48(), and mrand48() functions store
the last 48-bit X[i] generated into an internal buffer,
which is why they must be initialized prior to being
invoked.
The erand48(), nrand48(), and jrand48() functions require
that the calling program provide storage for the successive
X[i] values in the array pointed to by the xsubi
parameter. This 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 a parameter.
By using different parameters, the erand48(), nrand48(),
and jrand48() functions allow separate modules of a large
program to generate several independent sequences of pseudorandom
numbers; that is, the sequence of numbers that
one module generates does not depend upon how many times
the functions are called by other modules.
The initializer function srand48() sets the high-order 32
bits of X[i] to the LONG_BIT bits contained in its parameter.
The low-order 16 bits of X[i] are set to the arbitrary
hexadecimal value 330E.
The initializer function seed48() sets the value of X[i]
to the 48-bit value specified in the array pointed to by
the seed_16v parameter. In addition, seed48() returns a
pointer to a 48-bit internal buffer that contains the previous
value of X[i] which is used only by seed48(). The
returned pointer allows you to restart the pseudorandom
sequence at a given point. Use the pointer to copy the
previous X[i] value into a temporary array. To resume
where the original sequence left off, you can call
seed48() with a pointer to this array.
The lcong48() function specifies the initial X[i] value,
the multiplier value a, and the addend value c. The param
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() has been called, a subsequent call to
either srand48() or seed48() restores the standard a and c
as specified previously.
[POSIX] The drand48_r(), erand48_r(), jrand48_r(),
lcong48_r(), lrand48_r(), mrand48_r(), nrand48_r() l,
seed48_r(), and srand_r() functions are the reentrant versions
of drand48(), erand48(), jrand48(), lcong48(),
lrand48(), mrand48(), nrand48(), seed48(), and srand48().
[POSIX] Note that if the reentrant initialization functions
are not used prior to calling the random number generators,
the init field of the struct drand48_data structure
(passed to the random number generator functions)
must be cleared prior to calling them.
[POSIX] Note also, that the 48-bit internal buffer that
used to be returned by the seed48() function is now placed
in the DRAND48D structure in the lastx field by the
seed48_r() function.
The drand48() and erand48() functions return nonnegative,
double-precision, floating-point values.
The lrand48() and nrand48() functions return signed long
integers uniformly distributed over the range 0 <=y <
2^31.
The mrand48() and jrand48() functions return signed long
integers uniformly distributed over the range -2^31 <=y <
2^31.
The seed48() function returns a pointer to a 48-bit internal
buffer.
The lcong48() and srand48() functions do not return a
value.
[POSIX] Upon success, both the drand48_r() and
erand48_r() functions return a pointer (randval) to the
returned double value, and return a value of 0 (zero).
Upon success, both the mrand48_r() and jrand48_r() functions
have randval at the returned long value, and return
a value of 0 (zero). Upon success, the lcong48_r(),
seed48_r(), and srand48_r() return a value of 0 (zero).
The lrand48_r() and rand48_r() functions have randval
point at the returned long value, and return a value of 0
(zero). Upon error, the reentrant functions return a value
of -1, and set errno to [EFAULT].
[POSIX] Upon error, the drand48_r(), erand48_r(),
jrand48_r, lcong48_r, lrand48_r, mrand48_r, nrand48_r,
seed48_r, and srand_r functions return a value of -1, and
errno will be set to the following value: The dp, randval,
xsubi, param, or seed_16v value is invalid.
Functions: rand(3), random(3)
Standards: standards(5)
drand48(3)
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