diff options
| -rw-r--r-- | time/mktime.c | 46 |
1 files changed, 31 insertions, 15 deletions
diff --git a/time/mktime.c b/time/mktime.c index 72b2012..280f5f4 100644 --- a/time/mktime.c +++ b/time/mktime.c @@ -46,6 +46,21 @@ # define mktime my_mktime #endif /* DEBUG */ +/* 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 + INT_BITS is the number of useful bits in an int. GNU code can + assume that INT_BITS is at least 32. + + ISO C99 says that A >> B is implementation-defined if A < 0. Some + implementations (e.g., UNICOS 9.0 on a Cray Y-MP EL) don't shift + right in the usual way when A < 0, so SHR falls back on division if + ordinary A >> B doesn't seem to be the usual signed shift. */ +#define SHR(a, b) \ + (-1 >> 1 == -1 \ + ? (a) >> (b) \ + : (a) / (1 << (b)) - ((a) % (1 << (b)) < 0)) + /* The extra casts work around common compiler bugs. */ #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1)) /* The outer cast is needed to work around a bug in Cray C 5.0.3.0. @@ -60,14 +75,13 @@ #ifndef TIME_T_MAX # define TIME_T_MAX TYPE_MAXIMUM (time_t) #endif -#define TIME_T_MIDPOINT (((TIME_T_MIN + TIME_T_MAX) >> 1) + 1) +#define TIME_T_MIDPOINT (SHR (TIME_T_MIN + TIME_T_MAX, 1) + 1) /* Verify a requirement at compile-time (unlike assert, which is runtime). */ #define verify(name, assertion) struct name { char a[(assertion) ? 1 : -1]; } verify (time_t_is_integer, (time_t) 0.5 == 0); verify (twos_complement_arithmetic, -1 == ~1 + 1); -verify (right_shift_propagates_sign, -1 >> 1 == -1); /* 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. */ @@ -133,12 +147,12 @@ ydhms_diff (long int year1, long int yday1, int hour1, int min1, int sec1, /* Compute intervening leap days correctly even if year is negative. Take care to avoid integer overflow here. */ - int a4 = (year1 >> 2) + (TM_YEAR_BASE >> 2) - ! (year1 & 3); - int b4 = (year0 >> 2) + (TM_YEAR_BASE >> 2) - ! (year0 & 3); + int a4 = SHR (year1, 2) + SHR (TM_YEAR_BASE, 2) - ! (year1 & 3); + int b4 = SHR (year0, 2) + SHR (TM_YEAR_BASE, 2) - ! (year0 & 3); int a100 = a4 / 25 - (a4 % 25 < 0); int b100 = b4 / 25 - (b4 % 25 < 0); - int a400 = a100 >> 2; - int b400 = b100 >> 2; + int a400 = SHR (a100, 2); + int b400 = SHR (b100, 2); int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400); /* Compute the desired time in time_t precision. Overflow might @@ -322,14 +336,16 @@ __mktime_internal (struct tm *tp, int LOG2_YEARS_PER_BIENNIUM = 1; int approx_requested_biennia = - ((year_requested >> LOG2_YEARS_PER_BIENNIUM) - - ((EPOCH_YEAR - TM_YEAR_BASE) >> LOG2_YEARS_PER_BIENNIUM) - + (mday >> ALOG2_DAYS_PER_BIENNIUM) - + (hour >> ALOG2_HOURS_PER_BIENNIUM) - + (min >> ALOG2_MINUTES_PER_BIENNIUM) - + (LEAP_SECONDS_POSSIBLE ? 0 : sec >> ALOG2_SECONDS_PER_BIENNIUM)); - - int approx_biennia = t0 >> ALOG2_SECONDS_PER_BIENNIUM; + (SHR (year_requested, LOG2_YEARS_PER_BIENNIUM) + - SHR (EPOCH_YEAR - TM_YEAR_BASE, LOG2_YEARS_PER_BIENNIUM) + + SHR (mday, ALOG2_DAYS_PER_BIENNIUM) + + SHR (hour, ALOG2_HOURS_PER_BIENNIUM) + + SHR (min, ALOG2_MINUTES_PER_BIENNIUM) + + (LEAP_SECONDS_POSSIBLE + ? 0 + : SHR (sec, ALOG2_SECONDS_PER_BIENNIUM))); + + int approx_biennia = SHR (t0, ALOG2_SECONDS_PER_BIENNIUM); int diff = approx_biennia - approx_requested_biennia; int abs_diff = diff < 0 ? - diff : diff; @@ -347,7 +363,7 @@ __mktime_internal (struct tm *tp, /* Overflow occurred. Try repairing it; this might work if the time zone offset is enough to undo the overflow. */ time_t repaired_t0 = -1 - t0; - approx_biennia = repaired_t0 >> ALOG2_SECONDS_PER_BIENNIUM; + approx_biennia = SHR (repaired_t0, ALOG2_SECONDS_PER_BIENNIUM); diff = approx_biennia - approx_requested_biennia; abs_diff = diff < 0 ? - diff : diff; if (overflow_threshold < abs_diff) |