0,0 → 1,179 |
/* |
* Copyright (c) 1993 Martin Birgmeier |
* All rights reserved. |
* |
* You may redistribute unmodified or modified versions of this source |
* code provided that the above copyright notice and this and the |
* following conditions are retained. |
* |
* This software is provided ``as is'', and comes with no warranties |
* of any kind. I shall in no event be liable for anything that happens |
* to anyone/anything when using this software. |
*/ |
|
/* |
FUNCTION |
<<rand48>>, <<drand48>>, <<erand48>>, <<lrand48>>, <<nrand48>>, <<mrand48>>, <<jrand48>>, <<srand48>>, <<seed48>>, <<lcong48>>---pseudo-random number generators and initialization routines |
|
INDEX |
rand48 |
INDEX |
drand48 |
INDEX |
erand48 |
INDEX |
lrand48 |
INDEX |
nrand48 |
INDEX |
mrand48 |
INDEX |
jrand48 |
INDEX |
srand48 |
INDEX |
seed48 |
INDEX |
lcong48 |
|
ANSI_SYNOPSIS |
#include <stdlib.h> |
double drand48(void); |
double erand48(unsigned short <[xseed]>[3]); |
long lrand48(void); |
long nrand48(unsigned short <[xseed]>[3]); |
long mrand48(void); |
long jrand48(unsigned short <[xseed]>[3]); |
void srand48(long <[seed]>); |
unsigned short *seed48(unsigned short <[xseed]>[3]); |
void lcong48(unsigned short <[p]>[7]); |
|
TRAD_SYNOPSIS |
#include <stdlib.h> |
double drand48(); |
|
double erand48(<[xseed]>) |
unsigned short <[xseed]>[3]; |
|
long lrand48(); |
|
long nrand48(<[xseed]>) |
unsigned short <[xseed]>[3]; |
|
long mrand48(); |
|
long jrand48(<[xseed]>) |
unsigned short <[xseed]>[3]; |
|
void srand48(<[seed]>) |
long <[seed]>; |
|
unsigned short *seed48(<[xseed]>) |
unsigned short <[xseed]>[3]; |
|
void lcong48(<[p]>) |
unsigned short <[p]>[7]; |
|
DESCRIPTION |
The <<rand48>> family of functions generates pseudo-random numbers |
using a linear congruential algorithm working on integers 48 bits in size. |
The particular formula employed is |
r(n+1) = (a * r(n) + c) mod m |
where the default values are |
for the multiplicand a = 0xfdeece66d = 25214903917 and |
the addend c = 0xb = 11. The modulo is always fixed at m = 2 ** 48. |
r(n) is called the seed of the random number generator. |
|
For all the six generator routines described next, the first |
computational step is to perform a single iteration of the algorithm. |
|
<<drand48>> and <<erand48>> |
return values of type double. The full 48 bits of r(n+1) are |
loaded into the mantissa of the returned value, with the exponent set |
such that the values produced lie in the interval [0.0, 1.0]. |
|
<<lrand48>> and <<nrand48>> |
return values of type long in the range |
[0, 2**31-1]. The high-order (31) bits of |
r(n+1) are loaded into the lower bits of the returned value, with |
the topmost (sign) bit set to zero. |
|
<<mrand48>> and <<jrand48>> |
return values of type long in the range |
[-2**31, 2**31-1]. The high-order (32) bits of |
r(n+1) are loaded into the returned value. |
|
<<drand48>>, <<lrand48>>, and <<mrand48>> |
use an internal buffer to store r(n). For these functions |
the initial value of r(0) = 0x1234abcd330e = 20017429951246. |
|
On the other hand, <<erand48>>, <<nrand48>>, and <<jrand48>> |
use a user-supplied buffer to store the seed r(n), |
which consists of an array of 3 shorts, where the zeroth member |
holds the least significant bits. |
|
All functions share the same multiplicand and addend. |
|
<<srand48>> is used to initialize the internal buffer r(n) of |
<<drand48>>, <<lrand48>>, and <<mrand48>> |
such that the 32 bits of the seed value are copied into the upper 32 bits |
of r(n), with the lower 16 bits of r(n) arbitrarily being set to 0x330e. |
Additionally, the constant multiplicand and addend of the algorithm are |
reset to the default values given above. |
|
<<seed48>> also initializes the internal buffer r(n) of |
<<drand48>>, <<lrand48>>, and <<mrand48>>, |
but here all 48 bits of the seed can be specified in an array of 3 shorts, |
where the zeroth member specifies the lowest bits. Again, |
the constant multiplicand and addend of the algorithm are |
reset to the default values given above. |
<<seed48>> returns a pointer to an array of 3 shorts which contains |
the old seed. |
This array is statically allocated, thus its contents are lost after |
each new call to <<seed48>>. |
|
Finally, <<lcong48>> allows full control over the multiplicand and |
addend used in <<drand48>>, <<erand48>>, <<lrand48>>, <<nrand48>>, |
<<mrand48>>, and <<jrand48>>, |
and the seed used in <<drand48>>, <<lrand48>>, and <<mrand48>>. |
An array of 7 shorts is passed as parameter; the first three shorts are |
used to initialize the seed; the second three are used to initialize the |
multiplicand; and the last short is used to initialize the addend. |
It is thus not possible to use values greater than 0xffff as the addend. |
|
Note that all three methods of seeding the random number generator |
always also set the multiplicand and addend for any of the six |
generator calls. |
|
For a more powerful random number generator, see <<random>>. |
|
PORTABILITY |
SUS requires these functions. |
|
No supporting OS subroutines are required. |
*/ |
|
#include "rand48.h" |
|
void |
_DEFUN (__dorand48, (r, xseed), |
struct _reent *r _AND |
unsigned short xseed[3]) |
{ |
unsigned long accu; |
unsigned short temp[2]; |
|
_REENT_CHECK_RAND48(r); |
accu = (unsigned long) __rand48_mult[0] * (unsigned long) xseed[0] + |
(unsigned long) __rand48_add; |
temp[0] = (unsigned short) accu; /* lower 16 bits */ |
accu >>= sizeof(unsigned short) * 8; |
accu += (unsigned long) __rand48_mult[0] * (unsigned long) xseed[1] + |
(unsigned long) __rand48_mult[1] * (unsigned long) xseed[0]; |
temp[1] = (unsigned short) accu; /* middle 16 bits */ |
accu >>= sizeof(unsigned short) * 8; |
accu += __rand48_mult[0] * xseed[2] + __rand48_mult[1] * xseed[1] + __rand48_mult[2] * xseed[0]; |
xseed[0] = temp[0]; |
xseed[1] = temp[1]; |
xseed[2] = (unsigned short) accu; |
} |