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Diffstat (limited to 'src/common/mt_rand.c')
| -rw-r--r-- | src/common/mt_rand.c | 110 |
1 files changed, 110 insertions, 0 deletions
diff --git a/src/common/mt_rand.c b/src/common/mt_rand.c new file mode 100644 index 0000000..ab733ae --- /dev/null +++ b/src/common/mt_rand.c @@ -0,0 +1,110 @@ +/* +// This is the ``Mersenne Twister'' random number generator MT19937, which +// generates pseudorandom integers uniformly distributed in 0..(2^32 - 1) +// starting from any odd seed in 0..(2^32 - 1). This version is a recode +// by Shawn Cokus (Cokus@math.washington.edu) on March 8, 1998 of a version by +// Takuji Nishimura (who had suggestions from Topher Cooper and Marc Rieffel in +// July-August 1997). +// +// Effectiveness of the recoding (on Goedel2.math.washington.edu, a DEC Alpha +// running OSF/1) using GCC -O3 as a compiler: before recoding: 51.6 sec. to +// generate 300 million random numbers; after recoding: 24.0 sec. for the same +// (i.e., 46.5% of original time), so speed is now about 12.5 million random +// number generations per second on this machine. +// +// According to the URL <http://www.math.keio.ac.jp/~matumoto/emt.html> +// (and paraphrasing a bit in places), the Mersenne Twister is ``designed +// with consideration of the flaws of various existing generators,'' has +// a period of 2^19937 - 1, gives a sequence that is 623-dimensionally +// equidistributed, and ``has passed many stringent tests, including the +// die-hard test of G. Marsaglia and the load test of P. Hellekalek and +// S. Wegenkittl.'' It is efficient in memory usage (typically using 2506 +// to 5012 bytes of static data, depending on data type sizes, and the code +// is quite short as well). It generates random numbers in batches of 624 +// at a time, so the caching and pipelining of modern systems is exploited. +// It is also divide- and mod-free. +// +// This library is free software; you can redistribute it and/or modify it +// under the terms of the GNU Library General Public License as published by +// the Free Software Foundation (either version 2 of the License or, at your +// option, any later version). This library is distributed in the hope that +// it will be useful, but WITHOUT ANY WARRANTY, without even the implied +// warranty of 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. +// +// The code as Shawn received it included the following notice: +// +// Copyright (C) 1997 Makoto Matsumoto and Takuji Nishimura. When +// you use this, send an e-mail to <matumoto@math.keio.ac.jp> with +// an appropriate reference to your work. +// +// It would be nice to CC: <Cokus@math.washington.edu> when you write. +// +*/ + +#include <time.h> +#include "mt_rand.h" + +#define N (624) /* length of state vector */ +#define M (397) /* a period parameter */ +#define K (0x9908B0DFU) /* a magic constant */ +#define hiBit(u) ((u) & 0x80000000U) /* mask all but highest bit of u */ +#define loBit(u) ((u) & 0x00000001U) /* mask all but lowest bit of u */ +#define loBits(u) ((u) & 0x7FFFFFFFU) /* mask the highest bit of u */ +#define mixBits(u, v) (hiBit(u)|loBits(v)) /* move hi bit of u to hi bit of v */ + +static unsigned long state[N+1]; /* state vector + 1 extra to not violate ANSI C */ +static unsigned long *next; /* next random value is computed from here */ +static int left = -1; /* can *next++ this many times before reloading */ + + +void mt_seed(unsigned long seed) +{ + register unsigned long x = (seed | 1U) & 0xFFFFFFFFU, *s = state; + register int j; + + for(left=0, *s++=x, j=N; --j; + *s++ = (x*=69069U) & 0xFFFFFFFFU); +} + + +unsigned long mt_reload(void) +{ + register unsigned long *p0=state, *p2=state+2, *pM=state+M, s0, s1; + register int j; + + if(left < -1) + mt_seed(time(NULL)); + + left=N-1, next=state+1; + + for(s0=state[0], s1=state[1], j=N-M+1; --j; s0=s1, s1=*p2++) + *p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U); + + for(pM=state, j=M; --j; s0=s1, s1=*p2++) + *p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U); + + s1=state[0], *p0 = *pM ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U); + s1 ^= (s1 >> 11); + s1 ^= (s1 << 7) & 0x9D2C5680U; + s1 ^= (s1 << 15) & 0xEFC60000U; + return(s1 ^ (s1 >> 18)); +} + + +unsigned long mt_random(void) +{ + unsigned long y; + + if(--left < 0) + return(mt_reload()); + + y = *next++; + y ^= (y >> 11); + y ^= (y << 7) & 0x9D2C5680U; + y ^= (y << 15) & 0xEFC60000U; + return(y ^ (y >> 18)); +} |