Merge remote-tracking branch 'origin/master' into hjl/abi

2 files changed, 183 insertions, 62 deletions

diff --git a/ChangeLog b/ChangeLog
index 18e65a34d5..71045dbd47 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,50 @@
+2012-05-23  Paul Eggert  <eggert@cs.ucla.edu>
+
+	mktime: avoid signed integer overflow
+	* time/mktime.c (__mktime_internal): Do not mishandle the case
+	where diff == INT_MIN.
+
+	mktime: simplify computation of average
+	* time/mktime.c (ranged_convert): Use new time_t_avg function
+	instead of rolling our own (probably-slower) code.
+
+	mktime: do not assume signed right shift propagates sign bit
+	* time/mktime.c (isdst_differ): New static function.
+	(__mktime_internal): No need to normalize tm_isdst now.
+	(__mktime_internal, not_equal_tm): Use isdst_differ to compare
+	tm_isdst values.
+
+	mktime: merge another wrapv change from gnulib
+	* time/mktime.c (TYPE_MAXIMUM): Rework slightly to avoid diagnostics
+	from some compilers.
+
+	mktime: remove incorrect attempt at unusual arithmetics
+	* time/mktime.c (TYPE_ONES_COMPLEMENT, TYPE_SIGNED_MAGNITUDE): Remove.
+	The code didn't really work on such machines anyway.
+	(TYPE_MINIMUM): Assume two's complement.
+	(twos_complement_arithmetic): Verify that long_int and time_t
+	are two's complement (or unsigned, in the latter case).
+
+	mktime: check signed shifts on long_int and time_t, too
+	* time/mktime.c (SHR): Check that shifts work as desired
+	on the types long_int and time_t too, as SHR is used on
+	such types.
+
+	mktime: do not assume 'long' is wide enough
+	* time/mktime.c (verify): Move decl up.
+	(long_int): New type.
+	(leapyear, ydhms_diff, guess_time_tm, __mktime_internal): Use it,
+	to remove assumption in the code that 'long' is wide enough to
+	store year values.  This assumption is not true on x32 and on
+	some non-glibc platforms.
+
+	mktime: merge wrapv change from gnulib
+	* time/mktime.c (WRAPV): New macro.
+	(time_t_avg, time_t_add_ok, time_t_int_add_ok): New static functions.
+	(guess_time_tm, __mktime_internal): Do not assume that signed
+	integer overflow wraps around; modern compilers generate code
+	where this assumption is no longer valid.
+
 2012-05-23  H.J. Lu  <hongjiu.lu@intel.com>
 
 	* sysdeps/unix/sysv/linux/i386/sysdep.h (SYSCALL_ERROR_HANDLER):
diff --git a/time/mktime.c b/time/mktime.c
index 5058c4f27d..e1fbf9ea19 100644
--- a/time/mktime.c
+++ b/time/mktime.c
@@ -46,6 +46,39 @@
 # 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
+
+/* Verify a requirement at compile-time (unlike assert, which is runtime).  */
+#define verify(name, assertion) struct name { char a[(assertion) ? 1 : -1]; }
+
+/* A signed type that is at least one bit wider than int.  */
+#if INT_MAX <= LONG_MAX / 2
+typedef long int long_int;
+#else
+typedef long long int long_int;
+#endif
+verify (long_int_is_wide_enough, INT_MAX == INT_MAX * (long_int) 2 / 2);
+
 /* 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
@@ -56,9 +89,11 @@
    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)		\
+#define SHR(a, b)                                               \
+  ((-1 >> 1 == -1                                               \
+    && (long_int) -1 >> 1 == -1                                 \
+    && ((time_t) -1 >> 1 == -1 || ! TYPE_SIGNED (time_t)))      \
+   ? (a) >> (b)                                                 \
    : (a) / (1 << (b)) - ((a) % (1 << (b)) < 0))
 
 /* The extra casts in the following macros work around compiler bugs,
@@ -69,12 +104,8 @@
 #define TYPE_IS_INTEGER(t) ((t) 1.5 == 1)
 
 /* True if negative values of the signed integer type T use two's
-   complement, ones' complement, or signed magnitude representation,
-   respectively.  Much GNU code assumes two's complement, but some
-   people like to be portable to all possible C hosts.  */
+   complement, or if T is an unsigned integer type.  */
 #define TYPE_TWOS_COMPLEMENT(t) ((t) ~ (t) 0 == (t) -1)
-#define TYPE_ONES_COMPLEMENT(t) ((t) ~ (t) 0 == 0)
-#define TYPE_SIGNED_MAGNITUDE(t) ((t) ~ (t) 0 < (t) -1)
 
 /* True if the arithmetic type T is signed.  */
 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
@@ -86,13 +117,11 @@
 #define TYPE_MINIMUM(t) \
   ((t) (! TYPE_SIGNED (t) \
 	? (t) 0 \
-	: TYPE_SIGNED_MAGNITUDE (t) \
-	? ~ (t) 0 \
-	: ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1)))
+	: ~ TYPE_MAXIMUM (t)))
 #define TYPE_MAXIMUM(t) \
   ((t) (! TYPE_SIGNED (t) \
 	? (t) -1 \
-	: ~ (~ (t) 0 << (sizeof (t) * CHAR_BIT - 1))))
+	: ((((t) 1 << (sizeof (t) * CHAR_BIT - 2)) - 1) * 2 + 1)))
 
 #ifndef TIME_T_MIN
 # define TIME_T_MIN TYPE_MINIMUM (time_t)
@@ -102,14 +131,11 @@
 #endif
 #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, 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.  */
+verify (twos_complement_arithmetic,
+	(TYPE_TWOS_COMPLEMENT (int)
+	 && TYPE_TWOS_COMPLEMENT (long_int)
+	 && TYPE_TWOS_COMPLEMENT (time_t)));
 
 #define EPOCH_YEAR 1970
 #define TM_YEAR_BASE 1900
@@ -117,7 +143,7 @@ verify (base_year_is_a_multiple_of_100, TM_YEAR_BASE % 100 == 0);
 
 /* Return 1 if YEAR + TM_YEAR_BASE is a leap year.  */
 static inline int
-leapyear (long int year)
+leapyear (long_int year)
 {
   /* Don't add YEAR to TM_YEAR_BASE, as that might overflow.
      Also, work even if YEAR is negative.  */
@@ -151,6 +177,14 @@ const unsigned short int __mon_yday[2][13] =
 # include "mktime-internal.h"
 #endif
 
+/* Return 1 if the values A and B differ according to the rules for
+   tm_isdst: A and B differ if one is zero and the other positive.  */
+static int
+isdst_differ (int a, int b)
+{
+  return (!a != !b) && (0 <= a) && (0 <= b);
+}
+
 /* Return an integer value measuring (YEAR1-YDAY1 HOUR1:MIN1:SEC1) -
    (YEAR0-YDAY0 HOUR0:MIN0:SEC0) in seconds, assuming that the clocks
    were not adjusted between the time stamps.
@@ -163,12 +197,10 @@ const unsigned short int __mon_yday[2][13] =
    detect overflow.  */
 
 static inline time_t
-ydhms_diff (long int year1, long int yday1, int hour1, int min1, int sec1,
+ydhms_diff (long_int year1, long_int yday1, int hour1, int min1, int sec1,
 	    int year0, int yday0, int hour0, int min0, int sec0)
 {
   verify (C99_integer_division, -1 / 2 == 0);
-  verify (long_int_year_and_yday_are_wide_enough,
-	  INT_MAX <= LONG_MAX / 2 || TIME_T_MAX <= UINT_MAX);
 
   /* Compute intervening leap days correctly even if year is negative.
      Take care to avoid integer overflow here.  */
@@ -191,6 +223,53 @@ 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
@@ -199,7 +278,7 @@ ydhms_diff (long int year1, long int yday1, int hour1, int min1, int sec1,
    If overflow occurs, yield the minimal or maximal value, except do not
    yield a value equal to *T.  */
 static time_t
-guess_time_tm (long int year, long int yday, int hour, int min, int sec,
+guess_time_tm (long_int year, long_int yday, int hour, int min, int sec,
 	       const time_t *t, const struct tm *tp)
 {
   if (tp)
@@ -207,9 +286,8 @@ 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
@@ -241,9 +319,7 @@ ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
 	 they differ by 1.  */
       while (bad != ok + (bad < 0 ? -1 : 1))
 	{
-	  time_t mid = *t = (bad < 0
-			     ? bad + ((ok - bad) >> 1)
-			     : ok + ((bad - ok) >> 1));
+	  time_t mid = *t = time_t_avg (ok, bad);
 	  r = convert (t, tp);
 	  if (r)
 	    ok = mid;
@@ -292,9 +368,7 @@ __mktime_internal (struct tm *tp,
   int mday = tp->tm_mday;
   int mon = tp->tm_mon;
   int year_requested = tp->tm_year;
-  /* Normalize the value.  */
-  int isdst = ((tp->tm_isdst >> (8 * sizeof (tp->tm_isdst) - 1))
-	       | (tp->tm_isdst != 0));
+  int isdst = tp->tm_isdst;
 
   /* 1 if the previous probe was DST.  */
   int dst2;
@@ -303,8 +377,8 @@ __mktime_internal (struct tm *tp,
   int mon_remainder = mon % 12;
   int negative_mon_remainder = mon_remainder < 0;
   int mon_years = mon / 12 - negative_mon_remainder;
-  long int lyear_requested = year_requested;
-  long int year = lyear_requested + mon_years;
+  long_int lyear_requested = year_requested;
+  long_int year = lyear_requested + mon_years;
 
   /* The other values need not be in range:
      the remaining code handles minor overflows correctly,
@@ -316,8 +390,8 @@ __mktime_internal (struct tm *tp,
   int mon_yday = ((__mon_yday[leapyear (year)]
 		   [mon_remainder + 12 * negative_mon_remainder])
 		  - 1);
-  long int lmday = mday;
-  long int yday = mon_yday + lmday;
+  long_int lmday = mday;
+  long_int yday = mon_yday + lmday;
 
   time_t guessed_offset = *offset;
 
@@ -371,7 +445,7 @@ __mktime_internal (struct tm *tp,
 
       int approx_biennia = SHR (t0, ALOG2_SECONDS_PER_BIENNIUM);
       int diff = approx_biennia - approx_requested_biennia;
-      int abs_diff = diff < 0 ? - diff : diff;
+      int approx_abs_diff = diff < 0 ? -1 - diff : diff;
 
       /* IRIX 4.0.5 cc miscalculates TIME_T_MIN / 3: it erroneously
 	 gives a positive value of 715827882.  Setting a variable
@@ -382,15 +456,15 @@ __mktime_internal (struct tm *tp,
       time_t overflow_threshold =
 	(time_t_max / 3 - time_t_min / 3) >> ALOG2_SECONDS_PER_BIENNIUM;
 
-      if (overflow_threshold < abs_diff)
+      if (overflow_threshold < approx_abs_diff)
 	{
 	  /* 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 = SHR (repaired_t0, ALOG2_SECONDS_PER_BIENNIUM);
 	  diff = approx_biennia - approx_requested_biennia;
-	  abs_diff = diff < 0 ? - diff : diff;
-	  if (overflow_threshold < abs_diff)
+	  approx_abs_diff = diff < 0 ? -1 - diff : diff;
+	  if (overflow_threshold < approx_abs_diff)
 	    return -1;
 	  guessed_offset += repaired_t0 - t0;
 	  t0 = repaired_t0;
@@ -424,7 +498,7 @@ __mktime_internal (struct tm *tp,
 
   /* We have a match.  Check whether tm.tm_isdst has the requested
      value, if any.  */
-  if (isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
+  if (isdst_differ (isdst, tm.tm_isdst))
     {
       /* tm.tm_isdst has the wrong value.  Look for a neighboring
 	 time with the right value, and use its UTC offset.
@@ -457,22 +531,20 @@ __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 (! isdst_differ (isdst, otm.tm_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 +555,13 @@ __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;
     }
@@ -538,7 +612,7 @@ not_equal_tm (const struct tm *a, const struct tm *b)
 	  | (a->tm_mon ^ b->tm_mon)
 	  | (a->tm_year ^ b->tm_year)
 	  | (a->tm_yday ^ b->tm_yday)
-	  | (a->tm_isdst ^ b->tm_isdst));
+	  | isdst_differ (a->tm_isdst, b->tm_isdst));
 }
 
 static void