While preparing some proposed patches to historical data for Belfast, Dublin, and London, I noticed that zic miscompiles the latest tz data's March 1996 transition for Europe/Lisbon. Here's the line that is miscompiled: # Zone NAME GMTOFF RULES FORMAT [UNTIL] 1:00 EU MET%s 1996 Mar 31 1:00u Here is the zdump output: Europe/Lisbon Sat Mar 30 23:59:59 1996 GMT = Sun Mar 31 00:59:59 1996 MET isdst=0 Europe/Lisbon Sun Mar 31 00:00:00 1996 GMT = Sun Mar 31 01:00:00 1996 WET DST isdst=1 The transition should occur at 01:00 UTC, not 00:00 UTC. Here is a proposed patch. =================================================================== RCS file: RCS/zic.c,v retrieving revision 1996.8 retrieving revision 1996.8.1.1 diff -c -r1996.8 -r1996.8.1.1 *** zic.c 1996/05/16 18:00:12 1996.8 --- zic.c 1996/05/29 21:29:04 1996.8.1.1 *************** *** 1694,1704 **** ** Now we may get to set starttime for the next zone line. */ if (useuntil) { - starttime = tadd(zp->z_untiltime, -gmtoff); startttisstd = zp->z_untilrule.r_todisstd; startttisgmt = zp->z_untilrule.r_todisgmt; if (!startttisstd) starttime = tadd(starttime, -stdoff); } } writezone(zpfirst->z_name); --- 1694,1706 ---- ** Now we may get to set starttime for the next zone line. */ if (useuntil) { startttisstd = zp->z_untilrule.r_todisstd; startttisgmt = zp->z_untilrule.r_todisgmt; + starttime = zp->z_untiltime; if (!startttisstd) starttime = tadd(starttime, -stdoff); + if (!startttisgmt) + starttime = tadd(starttime, -gmtoff); } } writezone(zpfirst->z_name);