random() may yield different pseudo-random number sequences for the
same seed on another system. For instance, at least some versions of
MinGW provide a random() in -liberty that differs from traditional BSD
(see commit c8231b12). Rather inconvenient for regression testing.
MT19937 Mersenne Twister is a proven, high-quality PRNG. Actual code
is reference code provided by the inventors[*]. Quick tests show
performance comparable to random().
Like random(), MT is not cryptographically secure: observing enough of
its output permits guessing its state, and thus its future output. I
don't think players can do that.
Drop the copy of BSD random() we added for Windows.
Like the previous commit, this changes the server's die rolls, and
makes fairland create a different random map for the same seed. Update
expected smoke test results accordingly.
[*] mt19937ar.sep.tgz downloaded from
http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/MT2002/emt19937ar.html
"random() % n" is sound only when n is a power of two. The error is
hardly relevant in Empire, because random() yields 31 bits, and our n
are always much smaller than 2^31. Fix it anyway.
Use smallest the 2^m >= n instead of n, and discard numbers exceeding
n.
Bonus: faster for me even in the worst case n = 2^m+1.
Like the recent change to damage(), this changes some of the server's
die rolls, only this time the effect is pretty pervasive. Worse,
fairland now creates a completely different random map for the same
seed. Update expected smoke test results accordingly.
