On Apr 14, 2009, at 1:32 PM, Eric E. Dolecki wrote:
My apologies - what I meant to type was that I AM doing this:
int tmp = (arc4random()%10)+1;
while (tmp == activeTarget) {
tmp = (arc4random()%10)+1;
}
activeTarget = tmp;
This is for a game, so it's not very critical or anything. Someone
told me
that I might want to avoid a while loop at all by doing something
like this:
int result = (arc4random()%9) + 1;
if (result >= activeTarget) ++result;
activeTarget = result;
That seems a little odd to me to do things that way - but I'm not
really
sure.
For a game, you almost certainly don't care about the quality of your
random numbers. You don't need perfect statistical behavior (like a
physical simulation) or cryptographic un-guessability (like security
software). All you need is "looks random enough" and "fast".
In that case, arc4random() is overkill. That's a cryptographic random
number generator, so it's slow. random() would be faster and still
random enough. Just remember to call srandomdev() once at the start of
your program, or else you might get the same sequence of random
numbers every time you run.
The increment solution is a clever one that doesn't return the same
number twice in a row, but otherwise avoids unfairly returning some
numbers more often than others. (Try it - write a test program that
generates a few million numbers and counts the results.) It should be
as good as the try-again algorithm for your purposes, and faster.
--
Greg Parker gpar...@apple.com Runtime Wrangler
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