SECS_PER_DAY
diff_sec += SECS_PER_DAY;
diff_sec -= SECS_PER_DAY;
offset_day = offset_sec / SECS_PER_DAY;
offset_hms = offset_sec - (offset_day * SECS_PER_DAY);
if (offset_hms >= SECS_PER_DAY) {
offset_hms -= SECS_PER_DAY;
offset_hms += SECS_PER_DAY;
toffset = (long)off_day * SECS_PER_DAY + off_sec;