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code/source/mt.c

00001 /* A C-program for MT19937: Real number version    */
00002 /* genrand() generates one pseudorandom real number (double) */
00003 /* which is uniformly distributed on [0,1]-interval, for each */
00004 /* call. sgenrand(seed) set initial values to the working area */
00005 /* of 624 words. Before genrand(), sgenrand(seed) must be  */
00006 /* called once. (seed is any 32-bit integer except for 0).  */
00007 /* Integer generator is obtained by modifying two lines.  */
00008 /* Coded by Takuji Nishimura, considering the suggestions by */
00009 /* Topher Cooper and Marc Rieffel in July-Aug. 1997.   */
00010 
00011 /* This library is free software; you can redistribute it and/or */
00012 /* modify it under the terms of the GNU Library General Public  */
00013 /* License as published by the Free Software Foundation; either */
00014 /* version 2 of the License, or (at your option) any later   */
00015 /* version.              */
00016 /* This library is distributed in the hope that it will be useful, */
00017 /* but WITHOUT ANY WARRANTY; without even the implied warranty of */
00018 /* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.   */
00019 /* See the GNU Library General Public License for more details. */
00020 /* You should have received a copy of the GNU Library General  */
00021 /* Public License along with this library; if not, write to the */
00022 /* Free Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA */ 
00023 /* 02111-1307 USA             */
00024 
00025 /* Copyright (C) 1997 Makoto Matsumoto and Takuji Nishimura.  */
00026 /* Any feedback is very welcome. For any question, comments,  */
00027 /* see http://www.math.keio.ac.jp/matumoto/emt.html or email  */
00028 /* matumoto@math.keio.ac.jp          */
00029 
00030 #include <stdio.h> 
00031 
00032 /* Period parameters */ 
00033 #define N 624
00034 #define M 397
00035 #define MATRIX_A 0x9908b0df /* constant vector a */
00036 #define UPPER_MASK 0x80000000 /* most significant w-r bits */
00037 #define LOWER_MASK 0x7fffffff /* least significant r bits */
00038 
00039 /* Tempering parameters */ 
00040 #define TEMPERING_MASK_B 0x9d2c5680
00041 #define TEMPERING_MASK_C 0xefc60000
00042 #define TEMPERING_SHIFT_U(y) (y >> 11)
00043 #define TEMPERING_SHIFT_S(y) (y << 7)
00044 #define TEMPERING_SHIFT_T(y) (y << 15)
00045 #define TEMPERING_SHIFT_L(y) (y >> 18)
00046 
00047 static unsigned long mt[N]; /* the array for the state vector */
00048 static int mti=N+1; /* mti==N+1 means mt[N] is not initialized */
00049 
00050 /* initializing the array with a NONZERO seed */
00051 void
00052 sgenrand(unsigned long seed)
00053 
00054 {
00055         /* setting initial seeds to mt[N] using   */
00056         /* the generator Line 25 of Table 1 in   */
00057         /* [KNUTH 1981, The Art of Computer Programming */
00058         /* Vol. 2 (2nd Ed.), pp102]     */
00059         mt[0]= seed & 0xffffffff;
00060         for (mti=1; mti < N; mti++)
00061                 mt[mti] = (69069 * mt[mti-1]) & 0xffffffff;
00062 }
00063 
00064 double /* generating reals */
00065 /* unsigned long */ /* for integer generation */
00066 genrand()
00067 {
00068         unsigned long y;
00069         static unsigned long mag01[2]={0x0, MATRIX_A};
00070         /* mag01[x] = x * MATRIX_A for x=0,1 */
00071 
00072         if (mti >= N) { /* generate N words at one time */
00073                 int kk;
00074 
00075                 if (mti == N+1) /* if sgenrand() has not been called, */
00076                         sgenrand(4357); /* a default initial seed is used */
00077 
00078                 for (kk=0;kk < N-M;kk++) {
00079                         y = (mt[kk]&UPPER_MASK)|(mt[kk+1]&LOWER_MASK);
00080                         mt[kk] = mt[kk+M] ^ (y >> 1) ^ mag01[y & 0x1];
00081                 }
00082                 for (;kk < N-1;kk++) {
00083                         y = (mt[kk]&UPPER_MASK)|(mt[kk+1]&LOWER_MASK);
00084                         mt[kk] = mt[kk+(M-N)] ^ (y >> 1) ^ mag01[y & 0x1];
00085                 }
00086                 y = (mt[N-1]&UPPER_MASK)|(mt[0]&LOWER_MASK);
00087                 mt[N-1] = mt[M-1] ^ (y >> 1) ^ mag01[y & 0x1];
00088 
00089                 mti = 0;
00090         }
00091 
00092         y = mt[mti++];
00093         y ^= TEMPERING_SHIFT_U(y);
00094         y ^= TEMPERING_SHIFT_S(y) & TEMPERING_MASK_B;
00095         y ^= TEMPERING_SHIFT_T(y) & TEMPERING_MASK_C;
00096         y ^= TEMPERING_SHIFT_L(y);
00097 
00098         return ( (double)y / (unsigned long)0xffffffff ); /* reals */
00099         /* return y; */ /* for integer generation */
00100 }
00101 

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