Change from Norman Vine to add new random-number algorithm.

diff --git a/simgear/math/sg_random.c b/simgear/math/sg_random.c
index ec103f13a3e801a7f9b6e1b5364bc812e21ce968..fa3f213dac91a8cab62a7cc38bd09d4d5a39929b 100644 (file)
--- a/simgear/math/sg_random.c
+++ b/simgear/math/sg_random.c
@@ -22,59 +22,142 @@
 // $Id$
 
 
+/* 
+   A C-program for MT19937, with initialization improved 2002/2/10.
+   Coded by Takuji Nishimura and Makoto Matsumoto.
+   This is a faster version by taking Shawn Cokus's optimization,
+   Matthe Bellew's simplification, Isaku Wada's real version.
+
+   Before using, initialize the state by using init_genrand(seed) 
+   or init_by_array(init_key, key_length).
+
+   Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji Nishimura,
+   All rights reserved.                          
+
+   Redistribution and use in source and binary forms, with or without
+   modification, are permitted provided that the following conditions
+   are met:
+
+     1. Redistributions of source code must retain the above copyright
+        notice, this list of conditions and the following disclaimer.
+
+     2. Redistributions in binary form must reproduce the above copyright
+        notice, this list of conditions and the following disclaimer in the
+        documentation and/or other materials provided with the distribution.
+
+     3. The names of its contributors may not be used to endorse or promote 
+        products derived from this software without specific prior written 
+        permission.
+
+   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+   A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+   CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+   PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+   PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+   LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
+   Any feedback is very welcome.
+   http://www.math.keio.ac.jp/matumoto/emt.html
+   email: matumoto@math.keio.ac.jp
+*/
+
 #ifdef HAVE_CONFIG_H
 #  include <simgear_config.h>
 #endif
 
 #include <stdio.h>
-#include <stdlib.h>         // for random(), srandom(), drand48()
+#include <stdlib.h>         // for random(), srandom()
 #include <time.h>           // for time() to seed srandom()        
 
 #include "sg_random.h"
 
-#ifdef __SUNPRO_CC
-    extern "C" {
-       long int random();
-       void srandom(unsigned int seed);
+/* Period parameters */  
+#define N 624
+#define M 397
+#define MATRIX_A 0x9908b0dfUL   /* constant vector a */
+#define UMASK 0x80000000UL /* most significant w-r bits */
+#define LMASK 0x7fffffffUL /* least significant r bits */
+#define MIXBITS(u,v) ( ((u) & UMASK) | ((v) & LMASK) )
+#define TWIST(u,v) ((MIXBITS(u,v) >> 1) ^ ((v)&1UL ? MATRIX_A : 0UL))
+
+static unsigned long state[N]; /* the array for the state vector  */
+static int left = 1;
+static int initf = 0;
+static unsigned long *next;
+
+/* initializes state[N] with a seed */
+void init_genrand(unsigned long s)
+{
+    int j;
+    state[0]= s & 0xffffffffUL;
+    for (j=1; j<N; j++) {
+        state[j] = (1812433253UL * (state[j-1] ^ (state[j-1] >> 30)) + j); 
+        /* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
+        /* In the previous versions, MSBs of the seed affect   */
+        /* only MSBs of the array state[].                        */
+        /* 2002/01/09 modified by Makoto Matsumoto             */
+        state[j] &= 0xffffffffUL;  /* for >32 bit machines */
     }
-#endif
+    left = 1; initf = 1;
+}
+
+static void next_state(void)
+{
+    unsigned long *p=state;
+    int j;
+
+    /* if init_genrand() has not been called, */
+    /* a default initial seed is used         */
+    if (initf==0) init_genrand(5489UL);
+
+    left = N;
+    next = state;
+
+    for (j=N-M+1; --j; p++) 
+        *p = p[M] ^ TWIST(p[0], p[1]);
 
+    for (j=M; --j; p++) 
+        *p = p[M-N] ^ TWIST(p[0], p[1]);
+
+    *p = p[M-N] ^ TWIST(p[0], state[0]);
+}
 
 // Seed the random number generater with time() so we don't see the
 // same sequence every time
 void sg_srandom_time() {
-#ifdef HAVE_DRAND48
-    srand48(time(NULL) + getpid());
-#elif defined( HAVE_RANDOM )
-    srandom(time(NULL));
-#else
-    srand(time(NULL));
-#endif                                       
+    init_genrand(time(NULL));
 }
 
 
 // Seed the random number generater with your own seed so can set up
 // repeatable randomization.
 void sg_srandom( unsigned int seed ) {
-#ifdef HAVE_DRAND48
-    srand48( seed );
-#elif defined( HAVE_RANDOM )
-    srandom( seed );
-#else
-    srand( seed );
-#endif                                       
+    init_genrand( seed );
 }
 
 
 // return a random number between [0.0, 1.0)
 double sg_random() {
-#ifdef HAVE_DRAND48
-    return(drand48());
-#elif defined( HAVE_RANDOM )
-    return(random() / (double)RAND_MAX);
-#else
-    return(rand() / (double)RAND_MAX);
-#endif
+    unsigned long y;
+
+    if (--left == 0)
+               next_state();
+    y = *next++;
+
+    /* Tempering */
+    y ^= (y >> 11);
+    y ^= (y << 7) & 0x9d2c5680UL;
+    y ^= (y << 15) & 0xefc60000UL;
+    y ^= (y >> 18);
+
+    return (double)y * (1.0/4294967295.0); 
+    /* divided by 2^32-1 */ 
 }