[tz] localtime.c bugs

[Doug Bailey]

I've started working with tzcode2012b and I've run into a couple of issues.

The first: in testing, I found that if I set a timezone like "CST6", the tzname[] array would not be initialized.  Digging into it, I found that settzname[] depends on having transition rules for the zone, but a zone like "CST6" will only be created with a single type and no transitions.

To work around that one I've added the following code to initialize the tzname[] array from the ttis array before running through the types array:

+    for (i=0; i<sp->typecnt; i++) {
+        const struct ttinfo * const    ttisp = &sp->ttis[i];
+        tzname[ttisp->tt_isdst] = &sp->chars[ttisp->tt_abbrind];
+    }
    /*
    ** And to get the latest zone names into tzname. . .
    */
    for (i = 0; i < sp->timecnt; ++i) {
        register const struct ttinfo * const    ttisp =
                            &sp->ttis[
                                sp->types[i]];

The second has to do with our environment.  We have an unfortunate time_t definition: an unsigned 32-bit number.  The tzload code attempts to take unsigned time_t values into account, but if I'm not making a mistake understanding the way it's supposed to work, I think it has a few problems.

First, the loop over (i < sp->timecnt - 2) means that in comparing ats[i] > ats[i+1], you never compare ats[sp->timecnt-2] > ats[sp->timecnt-1].  This means that if all the transitions except the last are pre-epoch (negative number), the list doesn't get trimmed down.

Second, with that fixed, there are still problems with zones that only have pre-epoch transitions (e.g. America/Regina).  In such a case, the ats[i] > ats[i+1] case never triggers, so you're left with a list of ats[] values that aren't valid -- they're negative numbers in a system with an unsigned time_t.

This is rather uglier.  I've included my fix for what it's worth, but you can probably work out something better.  One thing to note: I try to preserve the last pre-epoch transition, to handle situations where there's a large gap in transitions between the start of the epoch the the first post-epoch transition.

        /*
        ** Out-of-sort ats should mean we're running on a
        ** signed time_t system but using a data file with
        ** unsigned values (or vice versa).
        */
#if 1
        for (i = 0; i <= sp->timecnt - 1; ++i)
            if ( (i < sp->timecnt-1 && sp->ats[i] > sp->ats[i + 1] ) ||
                    (i == sp->timecnt-1 && !TYPE_SIGNED(time_t) && sp->ats[i] > INT32_MAX) ) {
                if (TYPE_SIGNED(time_t)) {
                    /*
                    ** Ignore the end (easy).
                    */
                    sp->timecnt = i+1;
                } else {
                    /*
                    ** Ignore the beginning (harder).
                    */
                    register int    j;

                    // keep the record right before the epoch boundary, but
                    // tweak it so that it starts right with the epoch
                    sp->ats[i] = 0;

                    // move everything back...
                    if (i > 0) {
                        for (j = 0; j + i < sp->timecnt; ++j) {
                            sp->ats[j] = sp->ats[j + i];
                            sp->types[j] = sp->types[j + i];
                        }
                        sp->timecnt = j;
                    }
                }
                break;
            }
#else
        for (i = 0; i < sp->timecnt - 2; ++i)
            if (sp->ats[i] > sp->ats[i + 1]) {
                ++i;
                if (TYPE_SIGNED(time_t)) {
                    /*
                    ** Ignore the end (easy).
                    */
                    sp->timecnt = i;
                } else {
                    /*
                    ** Ignore the beginning (harder).
                    */
                    register int    j;

                    for (j = 0; j + i < sp->timecnt; ++j) {
                        sp->ats[j] = sp->ats[j + i];
                        sp->types[j] = sp->types[j + i];
                    }
                    sp->timecnt = j;
                }
                break;
            }
#endif

I appreciate any assistance with this.

Doug

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