DOS 'PDC_napmsl()' didn't round to the nearest clock tick correctly. The quantity added should have been 23590, about half the divisor 47181. With the incorrect value, naps would be one tick (about 55 milliseconds) shorter than they should be about 40% of the time. Unsurprisingly, nobody noticed. (But it was _wrong_.)

Author: Bill-Gray

common/dosutil.c

@@ -43,7 +43,7 @@ void PDC_napmsl( long ms)
            that would overflow,  and we'd need floating point math.
            47181/859 = MS_PER_DAY / MAX_TICK to within four parts per
            billion and won't overflow (because 0 <= ms <= MAX_NAP_SPAN). */
-    ticks_to_wait = (ms * 859L + 2359L) / 47181L;
+    ticks_to_wait = (ms * 859L + 23590L) / 47181L;
     if( ms && !ticks_to_wait)
         ticks_to_wait = 1;
     tick0 = getdosmemdword(0x46c);