On Fri, 10 Jul 1998, Chris Jacobson wrote:
>Mersenne Twister is LGPL, not GPL.
>Therefore, it could be used.
Ok, that's better, Slashdot said GPL'd, not LGPL'd. Still doesn't mean I
like it. Go compare the two source codes: (whitespace compressed)
unsigned long circle_random(void)
{
register int lo, hi, test;
hi = seed/q;
lo = seed%q;
test = a*lo - r*hi;
if (test > 0)
seed = test;
else
seed = test+ m;
return seed;
}
And the twister:
double /* generating reals */
/* unsigned long */ /* for integer generation */
genrand()
{
unsigned long y;
static unsigned long mag01[2]={0x0, MATRIX_A};
/* mag01[x] = x * MATRIX_A for x=0,1 */
if (mti >= N) { /* generate N words at one time */
int kk;
if (mti == N+1) /* if sgenrand() has not been called, */
sgenrand(4357); /* a default initial seed is used */
for (kk=0;kk<N-M;kk++) {
y = (mt[kk]&UPPER_MASK)|(mt[kk+1]&LOWER_MASK);
mt[kk] = mt[kk+M] ^ (y >> 1) ^ mag01[y & 0x1];
}
for (;kk<N-1;kk++) {
y = (mt[kk]&UPPER_MASK)|(mt[kk+1]&LOWER_MASK);
mt[kk] = mt[kk+(M-N)] ^ (y >> 1) ^ mag01[y & 0x1];
}
y = (mt[N-1]&UPPER_MASK)|(mt[0]&LOWER_MASK);
mt[N-1] = mt[M-1] ^ (y >> 1) ^ mag01[y & 0x1];
mti = 0;
}
y = mt[mti++];
y ^= TEMPERING_SHIFT_U(y);
y ^= TEMPERING_SHIFT_S(y) & TEMPERING_MASK_B;
y ^= TEMPERING_SHIFT_T(y) & TEMPERING_MASK_C;
y ^= TEMPERING_SHIFT_L(y);
return ( (double)y / (unsigned long)0xffffffff ); /* reals */
/* return y; */ /* for integer generation */
}
I think you'll see two real advantages to the current one:
1) No floating point math.
i.e.; "return ( (double)y / (unsigned long)0xffffffff ); /* reals */"
2) Much clearer.
Hypercompacted circle random:
register int test = a*(seed%q) - r*(seed/q);
return (seed = (test > 0 ? test : test + m));
--
George Greer, greerga@circlemud.org | Genius may have its limitations, but
http://patches.van.ml.org/ | stupidity is not thus handicapped.
http://www.van.ml.org/CircleMUD/ | -- Elbert Hubbard
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