diff options
Diffstat (limited to 'time/mktime.c')
| -rw-r--r-- | time/mktime.c | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/time/mktime.c b/time/mktime.c index c3c539526a..7fa5ccb23a 100644 --- a/time/mktime.c +++ b/time/mktime.c @@ -133,11 +133,19 @@ ydhms_tm_diff (year, yday, hour, min, sec, tp) int year, yday, hour, min, sec; const struct tm *tp; { - time_t ay = year + (time_t) (TM_YEAR_BASE - 1); - time_t by = tp->tm_year + (time_t) (TM_YEAR_BASE - 1); - time_t intervening_leap_days = - (ay/4 - by/4) - (ay/100 - by/100) + (ay/400 - by/400); - time_t years = ay - by; + /* Compute intervening leap days correctly even if year is negative. + Take care to avoid int overflow. time_t overflow is OK, since + only the low order bits of the correct time_t answer are needed. + Don't convert to time_t until after all divisions are done, since + time_t might be unsigned. */ + int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3); + int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3); + int a100 = a4 / 25 - (a4 % 25 < 0); + int b100 = b4 / 25 - (b4 % 25 < 0); + int a400 = a100 >> 2; + int b400 = b100 >> 2; + int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400); + time_t years = year - (time_t) tp->tm_year; time_t days = (365 * years + intervening_leap_days + (yday - tp->tm_yday)); return (60 * (60 * (24 * days + (hour - tp->tm_hour)) |