62 lines
1.8 KiB
Diff
62 lines
1.8 KiB
Diff
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2006-12-22 Paul Eggert <eggert@cs.ucla.edu>
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* lib/autoconf/functions.m4 (AC_FUNC_MKTIME):
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Include <limits.h>, and use its INT_MAX to rewrite the
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j loop so that it does not overflow 'int'. Problem reported by
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Ralf Wildenhues in
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<http://lists.gnu.org/archive/html/bug-gnulib/2006-12/msg00084.html>.
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Play it safe by shifting left by 1 rather than multiplying by 2,
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as GCC is less likely to optimize this away when the value
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is signed (when it assumes overflow leads to undefined behavior).
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Also, don't assume time_t uses two's complement.
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diff --git a/lib/autoconf/functions.m4 b/lib/autoconf/functions.m4
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index 185376e..a34c9f0 100644
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--- a/lib/autoconf/functions.m4
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+++ b/lib/autoconf/functions.m4
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@@ -984,6 +984,7 @@ AC_CACHE_CHECK([for working mktime], ac_cv_func_working_mktime,
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# endif
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#endif
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+#include <limits.h>
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#include <stdlib.h>
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#ifdef HAVE_UNISTD_H
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@@ -1132,12 +1133,15 @@ main ()
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isn't worth using anyway. */
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alarm (60);
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- for (time_t_max = 1; 0 < time_t_max; time_t_max *= 2)
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- continue;
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- time_t_max--;
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- if ((time_t) -1 < 0)
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- for (time_t_min = -1; (time_t) (time_t_min * 2) < 0; time_t_min *= 2)
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- continue;
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+ for (;;)
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+ {
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+ t = (time_t_max << 1) + 1;
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+ if (t <= time_t_max)
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+ break;
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+ time_t_max = t;
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+ }
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+ time_t_min = - ((time_t) ~ (time_t) 0 == (time_t) -1) - time_t_max;
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+
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delta = time_t_max / 997; /* a suitable prime number */
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for (i = 0; i < N_STRINGS; i++)
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{
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@@ -1152,10 +1156,12 @@ main ()
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&& mktime_test ((time_t) (60 * 60 * 24))))
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return 1;
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- for (j = 1; 0 < j; j *= 2)
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+ for (j = 1; ; j <<= 1)
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if (! bigtime_test (j))
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return 1;
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- if (! bigtime_test (j - 1))
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+ else if (INT_MAX / 2 < j)
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+ break;
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+ if (! bigtime_test (INT_MAX))
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return 1;
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}
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return ! (irix_6_4_bug () && spring_forward_gap () && year_2050_test ());
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