Updated to fedora-glibc-20041112T1640

2 files changed, 123 insertions, 52 deletions

diff --git a/time/difftime.c b/time/difftime.c
index 228090c057..ad896e207d 100644
--- a/time/difftime.c
+++ b/time/difftime.c
@@ -16,52 +16,107 @@
    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
    02111-1307 USA.  */
 
+/* Written by Paul Eggert <eggert@cs.ucla.edu>.  */
+
 #include <time.h>
-#include <values.h>
 
+#include <limits.h>
+#include <float.h>
+#include <stdint.h>
+
+#define TYPE_BITS(type) (sizeof (type) * CHAR_BIT)
+#define TYPE_FLOATING(type) ((type) 0.5 == 0.5)
+#define TYPE_SIGNED(type) ((type) -1 < 0)
+
+/* Return the difference between TIME1 and TIME0, where TIME0 <= TIME1.
+   time_t is known to be an integer type.  */
+
+static double
+subtract (time_t time1, time_t time0)
+{
+  if (! TYPE_SIGNED (time_t))
+    return time1 - time0;
+  else
+    {
+      /* Optimize the common special cases where time_t
+	 can be converted to uintmax_t without losing information.  */
+      uintmax_t dt = (uintmax_t) time1 - (uintmax_t) time0;
+      double delta = dt;
+
+      if (UINTMAX_MAX / 2 < INTMAX_MAX)
+	{
+	  /* This is a rare host where uintmax_t has padding bits, and possibly
+	     information was lost when converting time_t to uintmax_t.
+	     Check for overflow by comparing dt/2 to (time1/2 - time0/2).
+	     Overflow occurred if they differ by more than a small slop.
+	     Thanks to Clive D.W. Feather for detailed technical advice about
+	     hosts with padding bits.
+
+	     In the following code the "h" prefix means half.  By range
+	     analysis, we have:
+
+                  -0.5 <= ht1 - 0.5*time1 <= 0.5
+                  -0.5 <= ht0 - 0.5*time0 <= 0.5
+                  -1.0 <= dht - 0.5*(time1 - time0) <= 1.0
+
+             If overflow has not occurred, we also have:
+
+                  -0.5 <= hdt - 0.5*(time1 - time0) <= 0
+                  -1.0 <= dht - hdt <= 1.5
+
+             and since dht - hdt is an integer, we also have:
+
+                  -1 <= dht - hdt <= 1
+
+             or equivalently:
+
+                  0 <= dht - hdt + 1 <= 2
+
+             In the above analysis, all the operators have their exact
+             mathematical semantics, not C semantics.  However, dht - hdt +
+             1 is unsigned in C, so it need not be compared to zero.  */
+
+	  uintmax_t hdt = dt / 2;
+	  time_t ht1 = time1 / 2;
+	  time_t ht0 = time0 / 2;
+	  time_t dht = ht1 - ht0;
+
+	  if (2 < dht - hdt + 1)
+	    {
+	      /* Repair delta overflow.
+
+		 The following expression contains a second rounding,
+		 so the result may not be the closest to the true answer.
+		 This problem occurs only with very large differences.
+		 It's too painful to fix this portably.  */
+
+	      delta = dt + 2.0L * (UINTMAX_MAX - UINTMAX_MAX / 2);
+	    }
+	}
+
+      return delta;
+    }
+}
 
 /* Return the difference between TIME1 and TIME0.  */
 double
-__difftime (time1, time0)
-     time_t time1;
-     time_t time0;
+__difftime (time_t time1, time_t time0)
 {
-  /* Algorithm courtesy Paul Eggert (eggert@twinsun.com).  */
-
-  time_t delta, hibit;
+  /* Convert to double and then subtract if no double-rounding error could
+     result.  */
 
-  if (sizeof (time_t) < sizeof (double))
+  if (TYPE_BITS (time_t) <= DBL_MANT_DIG
+      || (TYPE_FLOATING (time_t) && sizeof (time_t) < sizeof (long double)))
     return (double) time1 - (double) time0;
-  if (sizeof (time_t) < sizeof (long double))
+
+  /* Likewise for long double.  */
+
+  if (TYPE_BITS (time_t) <= LDBL_MANT_DIG || TYPE_FLOATING (time_t))
     return (long double) time1 - (long double) time0;
 
-  if (time1 < time0)
-    return - __difftime (time0, time1);
-
-  /* As much as possible, avoid loss of precision by computing the
-    difference before converting to double.  */
-  delta = time1 - time0;
-  if (delta >= 0)
-    return delta;
-
-  /* Repair delta overflow.  */
-  hibit = (~ (time_t) 0) << (_TYPEBITS (time_t) - 1);
-
-  /* The following expression rounds twice, which means the result may not
-     be the closest to the true answer.  For example, suppose time_t is
-     64-bit signed int, long_double is IEEE 754 double with default
-     rounding, time1 = 9223372036854775807 and time0 = -1536.  Then the
-     true difference is 9223372036854777343, which rounds to
-     9223372036854777856 with a total error of 513.  But delta overflows to
-     -9223372036854774273, which rounds to -9223372036854774784, and
-     correcting this by subtracting 2 * (long_double) hibit (i.e. by adding
-     2**64 = 18446744073709551616) yields 9223372036854776832, which rounds
-     to 9223372036854775808 with a total error of 1535 instead.  This
-     problem occurs only with very large differences.  It's too painful to
-     fix this portably.  We are not alone in this problem; many C compilers
-     round twice when converting large unsigned types to small floating
-     types, so if time_t is unsigned the "return delta" above has the same
-     double-rounding problem.  */
-  return delta - 2 * (long double) hibit;
+  /* Subtract the smaller integer from the larger, convert the difference to
+     double, and then negate if needed.  */
+
+  return time1 < time0 ? - subtract (time0, time1) : subtract (time1, time0);
 }
 strong_alias (__difftime, difftime)
diff --git a/time/mktime.c b/time/mktime.c
index 72b20128a3..280f5f47d5 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)