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Diffstat (limited to 'src/common/mt_rand.cpp')
| -rw-r--r-- | src/common/mt_rand.cpp | 116 |
1 files changed, 116 insertions, 0 deletions
diff --git a/src/common/mt_rand.cpp b/src/common/mt_rand.cpp new file mode 100644 index 0000000..89872ad --- /dev/null +++ b/src/common/mt_rand.cpp @@ -0,0 +1,116 @@ +/* +// 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.hpp" + +#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 uint32_t state[N+1]; // state vector the +1 is needed due to the coding +static uint32_t *next; // next random value is computed from here +static int left = -1; // can *next++ this many times before reloading + +void mt_seed (uint32_t seed) +{ + uint32_t x = seed | 1U; + uint32_t *s = state; + left = 0; + + for (int j = N; *s++ = x, --j; x *= 69069U); +} + +void mt_reload (void) +{ + // if mt_seed has never been called + if (left < -1) + mt_seed (time (NULL)); + + // conceptually, these are indices into the state that wrap + uint32_t *p0 = state; + uint32_t *p2 = state + 2; + uint32_t *pM = state + M; + + uint32_t s0 = state[0]; + uint32_t s1 = state[1]; + + // regenerate the lower N-M elements of the state + for (int j = N-M+1; --j != 0; s0 = s1, s1 = *p2++) + *p0++ = *pM++ ^ (mixBits (s0, s1) >> 1) ^ (loBit (s1) ? K : 0U); + + pM = state; + // regenerate the next M-1 elements of the state + // note that s1 is set to state[N] at the end, but discarded + for (int j = M; --j != 0; s0 = s1, s1 = *p2++) + *p0++ = *pM++ ^ (mixBits (s0, s1) >> 1) ^ (loBit (s1) ? K : 0U); + + // regenerate the last 1 element of the state + s1 = state[0]; + *p0 = *pM ^ (mixBits (s0, s1) >> 1) ^ (loBit (s1) ? K : 0U); + + // ready for the normal mt_random algorithm + left = N; + next = state; +} + +uint32_t mt_random (void) +{ + if (--left < 0) + mt_reload (); + + uint32_t y = *next++; + y ^= (y >> 11); + y ^= (y << 7) & 0x9D2C5680U; + y ^= (y << 15) & 0xEFC60000U; + return y ^ (y >> 18); +} |