X-Git-Url: https://git.mxchange.org/?a=blobdiff_plain;f=simgear%2Fmath%2Fsg_random.c;h=d9f6bcb78f9c8642abc3ab32c2c807cd370e00e1;hb=584ee1364f25e5c3795f9ff4633a792cba39bfc7;hp=31297e19829624cb94487c15b0a3cc413e17c3df;hpb=75911b6c643d8e5597565bc63c34bdc2009a037a;p=simgear.git

diff --git a/simgear/math/sg_random.c b/simgear/math/sg_random.c
index 31297e19..d9f6bcb7 100644
--- a/simgear/math/sg_random.c
+++ b/simgear/math/sg_random.c
@@ -2,7 +2,7 @@
 //
 // Written by Curtis Olson, started July 1997.
 //
-// Copyright (C) 1997  Curtis L. Olson  - curt@infoplane.com
+// Copyright (C) 1997  Curtis L. Olson  - http://www.flightgear.org/~curt
 //
 // This library is free software; you can redistribute it and/or
 // modify it under the terms of the GNU Library General Public
@@ -14,16 +14,29 @@
 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 // Library General Public License for more details.
 //
-// You should have received a copy of the GNU Library General Public
-// License along with this library; if not, write to the
-// Free Software Foundation, Inc., 59 Temple Place - Suite 330,
-// Boston, MA  02111-1307, USA.
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software
+// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 //
 // $Id$
 
 
+/*
+ * "Cleaned up" and simplified Mersenne Twister implementation.
+ * Vastly smaller and more easily understood and embedded.  Stores the
+ * state in a user-maintained structure instead of static memory, so
+ * you can have more than one, or save snapshots of the RNG state.
+ * Lacks the "init_by_array()" feature of the original code in favor
+ * of the simpler 32 bit seed initialization.  Lacks the floating
+ * point generator, which is an orthogonal problem not related to
+ * random number generation.  Verified to be identical to the original
+ * MT199367ar code through the first 10M generated numbers.
+ */
+
+
+
 #ifdef HAVE_CONFIG_H
-#  include <config.h>
+#  include <simgear_config.h>
 #endif
 
 #include <stdio.h>
@@ -32,50 +45,70 @@
 
 #include "sg_random.h"
 
-#ifndef HAVE_RAND
-#  ifdef sgi
-#    undef RAND_MAX
-#    define RAND_MAX 2147483647
-#  endif
-#endif
+// Structure for the random number functions.
+mt random_seed;
+
+#define MT(i) mt->array[i]
+
+void mt_init(mt *mt, unsigned int seed)
+{
+    int i;
+    MT(0)= seed;
+    for(i=1; i<MT_N; i++)
+        MT(i) = (1812433253 * (MT(i-1) ^ (MT(i-1) >> 30)) + i);
+    mt->index = MT_N+1;
+}
+
+void mt_init_time_10(mt *mt)
+{
+  mt_init(mt, (unsigned int) time(NULL) / 600);  
+}
 
-#ifdef __SUNPRO_CC
-    extern "C" {
-	long int random();
-	void srandom(unsigned int seed);
+unsigned int mt_rand32(mt *mt)
+{
+    unsigned int i, y;
+    if(mt->index >= MT_N) {
+        for(i=0; i<MT_N; i++) {
+            y = (MT(i) & 0x80000000) | (MT((i+1)%MT_N) & 0x7fffffff);
+            MT(i) = MT((i+MT_M)%MT_N) ^ (y>>1) ^ (y&1 ? 0x9908b0df : 0);
+        }
+        mt->index = 0;
     }
-#endif
+    y = MT(mt->index++);
+    y ^= (y >> 11);
+    y ^= (y << 7) & 0x9d2c5680;
+    y ^= (y << 15) & 0xefc60000;
+    y ^= (y >> 18);
+    return y;
+}
 
+double mt_rand(mt *mt)
+{
+    /* divided by 2^32-1 */ 
+    return (double)mt_rand32(mt) * (1.0/4294967295.0); 
+}
 
 // Seed the random number generater with time() so we don't see the
 // same sequence every time
 void sg_srandom_time() {
-#ifdef HAVE_RAND
-    srand(time(NULL));
-#else
-    srandom(time(NULL));
-#endif                                       
+    mt_init(&random_seed, (unsigned int) time(NULL));
 }
 
+// Seed the random number generater with time() in 10 minute intervals
+// so we get the same sequence within 10 minutes interval.
+// This is useful for synchronizing two display systems.
+void sg_srandom_time_10() {
+    mt_init(&random_seed, (unsigned int) time(NULL) / 600);
+}
 
 // Seed the random number generater with your own seed so can set up
 // repeatable randomization.
 void sg_srandom( unsigned int seed ) {
-#ifdef HAVE_RAND
-    srand( seed );
-#else
-    srandom( seed );
-#endif                                       
+    mt_init(&random_seed, seed);
 }
 
-
 // return a random number between [0.0, 1.0)
 double sg_random() {
-#ifdef HAVE_RAND
-    return(rand() / (double)RAND_MAX);
-#else
-    return(random() / (double)RAND_MAX);
-#endif
+  return mt_rand(&random_seed);
 }
 
-