+++ /dev/null
-/* 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_CONFIG_H
-# include "config.h"
-#endif
-
-#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;
-}
projects / xscreensaver / blobdiff