109 lines
3.6 KiB
C
109 lines
3.6 KiB
C
#define HAVE_UNISTD_H 1
|
|
#define GETTIMEOFDAY_TWO_ARGS 1
|
|
/* yarandom.c -- Yet Another Random Number Generator.
|
|
|
|
The unportable mess that is rand(), random(), drand48() and friends led me
|
|
to ask Phil Karlton <karlton@netscape.com> what the Right Thing to Do was.
|
|
He responded with this. It is non-cryptographically secure, reasonably
|
|
random (more so than anything that is in any C library), and very fast.
|
|
|
|
I don't understand how it works at all, but he says "look at Knuth,
|
|
Vol. 2 (original edition), page 26, Algorithm A. In this case n=55,
|
|
k=20 and m=2^32."
|
|
|
|
So there you have it.
|
|
|
|
---------------------------
|
|
Note: xlockmore 4.03a10 uses this very simple RNG:
|
|
|
|
if ((seed = seed % 44488 * 48271 - seed / 44488 * 3399) < 0)
|
|
seed += 2147483647;
|
|
return seed-1;
|
|
|
|
of which it says
|
|
|
|
``Dr. Park's algorithm published in the Oct. '88 ACM "Random Number
|
|
Generators: Good Ones Are Hard To Find" His version available at
|
|
ftp://cs.wm.edu/pub/rngs.tar Present form by many authors.''
|
|
|
|
Karlton says: ``the usual problem with that kind of RNG turns out to
|
|
be unexepected short cycles for some word lengths.''
|
|
|
|
Karlton's RNG is faster, since it does three adds and two stores, while the
|
|
xlockmore RNG does two multiplies, two divides, three adds, and one store.
|
|
|
|
Compiler optimizations make a big difference here:
|
|
gcc -O: difference is 1.2x.
|
|
gcc -O2: difference is 1.4x.
|
|
gcc -O3: difference is 1.5x.
|
|
SGI cc -O: difference is 2.4x.
|
|
SGI cc -O2: difference is 2.4x.
|
|
SGI cc -O3: difference is 5.1x.
|
|
Irix 6.2; Indy r5k; SGI cc version 6; gcc version 2.7.2.1.
|
|
*/
|
|
|
|
#ifdef HAVE_UNISTD_H
|
|
#include <unistd.h> /* for getpid() */
|
|
#endif
|
|
#include <sys/time.h> /* for gettimeofday() */
|
|
|
|
#include "yarandom.h"
|
|
|
|
/* The following 'random' numbers are taken from CRC, 18th Edition, page 622.
|
|
Each array element was taken from the corresponding line in the table,
|
|
except that a[0] was from line 100. 8s and 9s in the table were simply
|
|
skipped. The high order digit was taken mod 4.
|
|
*/
|
|
#define VectorSize 55
|
|
static unsigned int a[VectorSize] = {
|
|
035340171546, 010401501101, 022364657325, 024130436022, 002167303062, /* 5 */
|
|
037570375137, 037210607110, 016272055420, 023011770546, 017143426366, /* 10 */
|
|
014753657433, 021657231332, 023553406142, 004236526362, 010365611275, /* 14 */
|
|
007117336710, 011051276551, 002362132524, 001011540233, 012162531646, /* 20 */
|
|
007056762337, 006631245521, 014164542224, 032633236305, 023342700176, /* 25 */
|
|
002433062234, 015257225043, 026762051606, 000742573230, 005366042132, /* 30 */
|
|
012126416411, 000520471171, 000725646277, 020116577576, 025765742604, /* 35 */
|
|
007633473735, 015674255275, 017555634041, 006503154145, 021576344247, /* 40 */
|
|
014577627653, 002707523333, 034146376720, 030060227734, 013765414060, /* 45 */
|
|
036072251540, 007255221037, 024364674123, 006200353166, 010126373326, /* 50 */
|
|
015664104320, 016401041535, 016215305520, 033115351014, 017411670323 /* 55 */
|
|
};
|
|
|
|
static int i1, i2;
|
|
|
|
unsigned int ya_random(void)
|
|
{
|
|
register int ret = a[i1] + a[i2];
|
|
a[i1] = ret;
|
|
if (++i1 >= VectorSize)
|
|
i1 = 0;
|
|
if (++i2 >= VectorSize)
|
|
i2 = 0;
|
|
return ret;
|
|
}
|
|
|
|
void ya_rand_init(unsigned int seed)
|
|
{
|
|
int i;
|
|
if (seed == 0) {
|
|
struct timeval tp;
|
|
#ifdef GETTIMEOFDAY_TWO_ARGS
|
|
struct timezone tzp;
|
|
gettimeofday(&tp, &tzp);
|
|
#else
|
|
gettimeofday(&tp);
|
|
#endif
|
|
/* ignore overflow */
|
|
seed = (999 * tp.tv_sec) + (1001 * tp.tv_usec) + (1003 * getpid());
|
|
}
|
|
|
|
a[0] += seed;
|
|
for (i = 1; i < VectorSize; i++) {
|
|
seed = a[i - 1] * 1001 + seed * 999;
|
|
a[i] += seed;
|
|
}
|
|
|
|
i1 = a[0] % VectorSize;
|
|
i2 = (i1 + 024) % VectorSize;
|
|
}
|