Re: Re: [Tinycc-devel] fib.c

[Laszlo Hars]

Dave,

Your code is a nice demonstration of a general technique to convert
loops to (tail)recursive calls, by passing the loop variable and the
list of changed variables as parameters. It is a good test for the
optimization capabilities of the compiler: it should convert the code
back to iterative (loop) form. Otherwise, one should use something like
this:

typedef unsigned long long UI64;

UI64 fib(int const n)
{
    int i; UI64 t, a = 0, b = 1;
    for( i = 1; i < n && a <= b; ++i) {
        t = b; b += a, a = t; }
    return b < a ? 0 : b;
}

Your code and this one relies on the "wrap-around at overflow" behavior
of the compiler. I did not find it documented. Have I missed it? There
are compilers, which return the largest possible number at an overflow,
others return some special value. Is it safe to rely on this
wrap-around?

Laszlo Hars