Hmmm...if a binary file has 32-bit values that are in sort and that all have their
high-order bits set, it might be because it contains signed values that are all
pre-epoch. It might also be because it contains unsigned values that are all
post-2038--that's unlikely now, but likelier as time goes by.

If we're lucky, 32-bit systems will be a thing of the past by the time it's likely.
That being so, I've attached a slightly-revised version of Doug Bailey's fixes
(they also appear below, with tabs mangled by Firefox/Gmail).

Are there any present-day systems with unsigned 64-bit time_t's?

        --ado

8.17
2110 lines
8.18
2127 lines
*** /tmp/,alocaltime.c    2012-07-10 15:14:38.372363200 -0400
--- /tmp/,blocaltime.c    2012-07-10 15:14:38.509371000 -0400
***************
*** 5,11 ****

#ifndef lint
#ifndef NOID
! static char    elsieid[] = "@(#)localtime.c    8.17";
#endif /* !defined NOID */
#endif /* !defined lint */

--- 5,11 ----

#ifndef lint
#ifndef NOID
! static char    elsieid[] = "@(#)localtime.c    8.18";
#endif /* !defined NOID */
#endif /* !defined lint */

***************
*** 277,282 ****
--- 277,287 ----
    /*
    ** And to get the latest zone names into tzname. . .
    */
+     for (i = 0; i < sp->typecnt; ++i) {
+         register const struct ttinfo * const    ttisp = &sp->ttis[i];
+
+         tzname[ttisp->tt_isdst] = &sp->chars[ttisp->tt_abbrind];
+     }
    for (i = 0; i < sp->timecnt; ++i) {
        register const struct ttinfo * const    ttisp =
                            &sp->ttis[
***************
*** 489,508 ****
        ** signed time_t system but using a data file with
        ** unsigned values (or vice versa).
        */
!         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];
--- 494,525 ----
        ** signed time_t system but using a data file with
        ** unsigned values (or vice versa).
        */
!         for (i = 0; i < sp->timecnt; ++i)
!             if ((i < sp->timecnt - 1 &&
!                 sp->ats[i] > sp->ats[i + 1]) ||
!                 (i == sp->timecnt - 1 &&
!                 !TYPE_SIGNED(time_t) &&
!                 stored == 4 &&
!                 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
+                     ** (thanks to Doug Bailey).
+                     */
+                     sp->ats[i] = 0;
                    for (j = 0; j + i < sp->timecnt; ++j) {
                        sp->ats[j] = sp->ats[j + i];
                        sp->types[j] = sp->types[j + i];