#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 generates pseudo-random numbers using a linear
congruential algorithm and 48-bit integer arithmetic.
The srand48(), seed48()
and lcong48() functions are initialization entry points,
one of which should be invoked before any of drand48(),
lrand48(), or mrand48() is called.
Although it is not recommended practice, constant default initializer
values are supplied automatically if drand48(),
lrand48(), or mrand48()
is called without a prior call to an initialization entry point.
The erand48(), jrand48(),
and nrand48() 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,
Xi, according to the linear
congruential formula:
The parameter m=248; hence 48-bit integer
arithmetic is performed.
Unless lcong48() is invoked,
the multiplier value a and the addend value c
are given by:
a=5DEECE66D16=2736731631558
c=B16=138
The value returned by any of the drand48(),
erand48(), jrand48(),
lrand48(), mrand48(),
or nrand48() functions is computed by
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 (leftmost)
bits of Xi and transformed into the return
value.
The drand48(), lrand48()
and mrand48() functions store the last 48-bit
Xi in generated in an internal buffer;
that is why they must be initialized prior to being invoked.
The erand48(), jrand48()
and nrand48() functions require the calling program to
provide storage for the successive Xi values in
the array specified as a parameter when the functions are invoked.
This is why these routines do not have to be initialized; the
calling program merely has to place the desired initial value of
Xi into the array and pass it as an argument.
By using different arguments, erand48(),
jrand48() and nrand48()
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 does 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 Xi to the low-order 32 bits contained
in its argument. The low-order 16 bits of Xi
are set to the arbitrary value 330E16.
The initializer function seed48() sets the value
Xi to the 48-bit value specified
in the argument array.
In addition, the previous value of Xi
is copied into a 48-bit internal buffer, used only by
seed48(), and a pointer to this buffer is
returned by seed48(). This
returned pointer, which can 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
Xi value, and then use this value to
re-initialize via seed48() when the program is restarted.
The initializer function lcong48()
allows the user to specify the initial Xi, the
multiplier value a, and the addend value c.
After lcong48() is called, a subsequent call to
either srand48() or seed48()
restores the standard multiplier and addend values, a
and c, as specified earlier.
- xsubi
-
Specifies the next value for Xi in the linear
congruential formula described earlier.
The functions erand48(), jrand48()
and nrand48() fill in this array on each iteration;
prior to calling any of these functions for the first time,
this array should be initialized with the first Xi
value.
- param
-
Specifies the initial Xi,
the multiplier value a, and the addend value c,
for the linear congruential formula described above.
Array elements param[0-2] specify Xi,
param[3-5] specify the multiplier a, and
param[6] specifies the 16-bit addend c.
- seed16v
-
Specifies the value of Xi
in the linear congruential formula described above. The
low-order 16 bits of Xi are set to the
low-order 16 bits of seed16v[0]. The mid-order 16
bits of Xi are set to the low-order 16
bits of seed16v[1].
The high-order 16 bits of Xi
are set to the low-order 16 bits of seed16v[2].
- seedval
-
Specifies the high-order
32 bits of Xi. The low-order 16 bits of
Xi are set to the arbitrary value 330E16.
The drand48() and erand48()
functions return non-negative, double-precision, floating point
values, uniformly distributed over the interval [0.0,1.0).
The lrand48() and nrand48()
functions return non-negative, long integers, uniformly
distributed over the interval [0,231).
The mrand48() and jrand48()
functions return signed long integers uniformly distributed over
the interval [-231,231).
The seed48() function returns a pointer to a buffer
containing the previous value of Xi.
The lcong48() and srand48()
functions return nothing.
UNIX 98
drand48(), lrand48(), mrand48(): Unsafe
erand48(), jrand48(), lcong48(), nrand48(), seed48(), srand48(): MT-Safe.
None.
PTC MKS Toolkit for Professional Developers
PTC MKS Toolkit for Professional Developers 64-Bit Edition
PTC MKS Toolkit for Enterprise Developers
PTC MKS Toolkit for Enterprise Developers 64-Bit Edition
- Functions:
- initstate(), rand(), rand_r(), random(), srand(), srandom()
PTC MKS Toolkit 10.5 Documentation Build 40.
