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[BZ #541]

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2004-11-10  Paul Eggert  <eggert@cs.ucla.edu>
	[BZ #541]
	* time/mktime.c (SHR): New macro, which is a portable
	substitute for >> that should work even on Crays.
	(TIME_T_MIDPOINT, ydhms_diff, __mktime_internal): Use it.
	Problem reported by Mark D. Baushke in
	<http://lists.gnu.org/archive/html/bug-gnulib/2004-11/msg00071.html>.
This commit is contained in:
Roland McGrath 2004-11-11 00:28:17 +00:00
parent cb265fec1b
commit 1c67fabdb8
1 changed files with 30 additions and 14 deletions
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44
time/mktime.c
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@ -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));
(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 = t0 >> 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)