[gameprogrammer] Re: Random Integer Problem :(

Andrew Falgout wrote:
> Perhaps you can explain why the modulus would be the improper way of
> getting a random number? 

Because it isn't a random number with infinite range.

If you look at RAND_MAX modulo an integer X (the range you want, 6 or 10
or whatever) it's very unlikely to be zero.  If the modulus is non-zero,
and the random number generator is truly random, then the result you get
is subtly weighted to the lower numbers.

If RAND_MAX were 10 and the range you wanted was 6, then the range is

        0-9 % 6 = (0, 1, 2, 3, 4, 5, 0, 1, 2, 3)

As you can see, a third of the numbers (4 and 5) are half as likely to
be the result as the smaller numbers are.

For sufficiently large RAND_MAX this doesn't much matter to most people,
although cryptographers have to worry about statistical-based attacks.
For games... it really shouldn't matter.
-- 
 Matthew Weigel



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