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Diffstat (limited to 'firmware/libc/random.c')
| -rw-r--r-- | firmware/libc/random.c | 119 |
1 files changed, 119 insertions, 0 deletions
diff --git a/firmware/libc/random.c b/firmware/libc/random.c new file mode 100644 index 0000000..f3efe89 --- /dev/null +++ b/firmware/libc/random.c @@ -0,0 +1,119 @@ +/* + 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. + + Before using, initialize the state by using srand(seed). + + 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.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html + email: m-mat @ math.sci.hiroshima-u.ac.jp (remove space) +*/ + +/* + Adapted to Rockbox by Jens Arnold +*/ + +#include <stdlib.h> + +/* 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 = 0; +static unsigned long *next; + +/* initializes state[N] with a seed */ +void srand(unsigned int seed) +{ + unsigned long x = seed & 0xffffffffUL; + unsigned long *s = state; + int j; + + for (*s++ = x, j = 1; j < N; j++) { + x = (1812433253UL * (x ^ (x >> 30)) + j) & 0xffffffffUL; + *s++ = x; + /* 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 */ + } + left = 1; +} + +static void next_state(void) +{ + unsigned long *p = state; + int j; + + /* if srand() has not been called, */ + /* a default initial seed is used */ + if (left < 0) + srand(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]); +} + +/* generates a random number on [0,RAND_MAX]-interval */ +int rand(void) +{ + 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 ((unsigned int)y) >> 1; +} |