UB external runs fine ppc and PC crashes Intel Mac

Greetings to all... I am new to developing Max externals, and a relatively inexperienced C programmer. That said, I'm trying to develop a set of simple objects for use with Just Intonation, and have been cheerfully coding away over the past weeks until I hit a strange snag. My latest object compiles successfully in Xcode 2.5 (this works on both PPC G4 and on Mac Intel platforms), producing a universal binary object which loads on both platforms. (It also works on PC and on a G5). On the PPC it does exactly what it should, and on an Intel Mac it crashes as soon as it receives a number in inlet 1.

I've isolated what causes the crash, and it is a very simple subroutine that performs a search, given a starting input value (t) and a test value (l). The bit of code looks like this:

int ftti_searchdown(int t, int l)

/* brute-force search downwards matches within prime limit (l) or returns -1 */

{
    int check, t_in;

    t_in=t;
    if (t > 0) {
        t--;
        check = ftti_TIpl(t);

/* ftti_TIpl returns values from a lookup table of prime limit values which range between 1 and 23 */

        while ((check > l)&&(t > 0)) {
            t--;
            check = ftti_TIpl(t);
        }
    }
    if (t == t_in) {
        t = -1;
    }
    return t;

/* search returns -1 if it failed */

}

If there is anyone willing to check this out, I would appreciate any suggestions. I've attached a zip archives, containing my Xcode project folder, the compiled external, a test patch and a crash report.

best regards and many thanks in advance
Marc

PS subfolders:
ftti-sabat has the external, a test patch, and the crash report
ffti-xcode is my source code file ftti.c and related files: Info.plist, ftti.xcodeproj, ftti.def