diff options
Diffstat (limited to 'time/mktime.c')
| -rw-r--r-- | time/mktime.c | 115 |
1 files changed, 90 insertions, 25 deletions
diff --git a/time/mktime.c b/time/mktime.c index 5058c4f27d..8a2b22881b 100644 --- a/time/mktime.c +++ b/time/mktime.c @@ -46,6 +46,28 @@ # define mktime my_mktime #endif /* DEBUG */ +/* Some of the code in this file assumes that signed integer overflow + silently wraps around. This assumption can't easily be programmed + around, nor can it be checked for portably at compile-time or + easily eliminated at run-time. + + Define WRAPV to 1 if the assumption is valid and if + #pragma GCC optimize ("wrapv") + does not trigger GCC bug 51793 + <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51793>. + Otherwise, define it to 0; this forces the use of slower code that, + while not guaranteed by the C Standard, works on all production + platforms that we know about. */ +#ifndef WRAPV +# if (((__GNUC__ == 4 && 4 <= __GNUC_MINOR__) || 4 < __GNUC__) \ + && defined __GLIBC__) +# pragma GCC optimize ("wrapv") +# define WRAPV 1 +# else +# define WRAPV 0 +# endif +#endif + /* Shift A right by B bits portably, by dividing A by 2**B and truncating towards minus infinity. A and B should be free of side effects, and B should be in the range 0 <= B <= INT_BITS - 2, where @@ -107,9 +129,6 @@ verify (time_t_is_integer, TYPE_IS_INTEGER (time_t)); verify (twos_complement_arithmetic, TYPE_TWOS_COMPLEMENT (int)); -/* The code also assumes that signed integer overflow silently wraps - around, but this assumption can't be stated without causing a - diagnostic on some hosts. */ #define EPOCH_YEAR 1970 #define TM_YEAR_BASE 1900 @@ -191,6 +210,53 @@ ydhms_diff (long int year1, long int yday1, int hour1, int min1, int sec1, return seconds; } +/* Return the average of A and B, even if A + B would overflow. */ +static time_t +time_t_avg (time_t a, time_t b) +{ + return SHR (a, 1) + SHR (b, 1) + (a & b & 1); +} + +/* Return 1 if A + B does not overflow. If time_t is unsigned and if + B's top bit is set, assume that the sum represents A - -B, and + return 1 if the subtraction does not wrap around. */ +static int +time_t_add_ok (time_t a, time_t b) +{ + if (! TYPE_SIGNED (time_t)) + { + time_t sum = a + b; + return (sum < a) == (TIME_T_MIDPOINT <= b); + } + else if (WRAPV) + { + time_t sum = a + b; + return (sum < a) == (b < 0); + } + else + { + time_t avg = time_t_avg (a, b); + return TIME_T_MIN / 2 <= avg && avg <= TIME_T_MAX / 2; + } +} + +/* Return 1 if A + B does not overflow. */ +static int +time_t_int_add_ok (time_t a, int b) +{ + verify (int_no_wider_than_time_t, INT_MAX <= TIME_T_MAX); + if (WRAPV) + { + time_t sum = a + b; + return (sum < a) == (b < 0); + } + else + { + int a_odd = a & 1; + time_t avg = SHR (a, 1) + (SHR (b, 1) + (a_odd & b)); + return TIME_T_MIN / 2 <= avg && avg <= TIME_T_MAX / 2; + } +} /* Return a time_t value corresponding to (YEAR-YDAY HOUR:MIN:SEC), assuming that *T corresponds to *TP and that no clock adjustments @@ -207,9 +273,8 @@ guess_time_tm (long int year, long int yday, int hour, int min, int sec, time_t d = ydhms_diff (year, yday, hour, min, sec, tp->tm_year, tp->tm_yday, tp->tm_hour, tp->tm_min, tp->tm_sec); - time_t t1 = *t + d; - if ((t1 < *t) == (TYPE_SIGNED (time_t) ? d < 0 : TIME_T_MAX / 2 < d)) - return t1; + if (time_t_add_ok (*t, d)) + return *t + d; } /* Overflow occurred one way or another. Return the nearest result @@ -457,22 +522,20 @@ __mktime_internal (struct tm *tp, for (delta = stride; delta < delta_bound; delta += stride) for (direction = -1; direction <= 1; direction += 2) - { - time_t ot = t + delta * direction; - if ((ot < t) == (direction < 0)) - { - struct tm otm; - ranged_convert (convert, &ot, &otm); - if (otm.tm_isdst == isdst) - { - /* We found the desired tm_isdst. - Extrapolate back to the desired time. */ - t = guess_time_tm (year, yday, hour, min, sec, &ot, &otm); - ranged_convert (convert, &t, &tm); - goto offset_found; - } - } - } + if (time_t_int_add_ok (t, delta * direction)) + { + time_t ot = t + delta * direction; + struct tm otm; + ranged_convert (convert, &ot, &otm); + if (otm.tm_isdst == isdst) + { + /* We found the desired tm_isdst. + Extrapolate back to the desired time. */ + t = guess_time_tm (year, yday, hour, min, sec, &ot, &otm); + ranged_convert (convert, &t, &tm); + goto offset_found; + } + } } offset_found: @@ -483,11 +546,13 @@ __mktime_internal (struct tm *tp, /* Adjust time to reflect the tm_sec requested, not the normalized value. Also, repair any damage from a false match due to a leap second. */ int sec_adjustment = (sec == 0 && tm.tm_sec == 60) - sec; + if (! time_t_int_add_ok (t, sec_requested)) + return -1; t1 = t + sec_requested; + if (! time_t_int_add_ok (t1, sec_adjustment)) + return -1; t2 = t1 + sec_adjustment; - if (((t1 < t) != (sec_requested < 0)) - | ((t2 < t1) != (sec_adjustment < 0)) - | ! convert (&t2, &tm)) + if (! convert (&t2, &tm)) return -1; t = t2; } |