Prepare for radical source tree reorganization. zack/build-layout-experiment

All top-level files and directories are moved into a temporary storage
directory, REORG.TODO, except for files that will certainly still
exist in their current form at top level when we're done (COPYING,
COPYING.LIB, LICENSES, NEWS, README), all old ChangeLog files (which
are moved to the new directory OldChangeLogs, instead), and the
generated file INSTALL (which is just deleted; in the new order, there
will be no generated files checked into version control).

1 files changed, 121 insertions, 0 deletions

diff --git a/REORG.TODO/time/difftime.c b/REORG.TODO/time/difftime.c
new file mode 100644
index 0000000000..e5e3311744
--- /dev/null
+++ b/REORG.TODO/time/difftime.c
@@ -0,0 +1,121 @@
+/* Copyright (C) 1991-2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* Written by Paul Eggert <eggert@cs.ucla.edu>.  */
+
+#include <time.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 (time_t time1, time_t time0)
+{
+  /* Convert to double and then subtract if no double-rounding error could
+     result.  */
+
+  if (TYPE_BITS (time_t) <= DBL_MANT_DIG
+      || (TYPE_FLOATING (time_t) && sizeof (time_t) < sizeof (long double)))
+    return (double) time1 - (double) time0;
+
+  /* Likewise for long double.  */
+
+  if (TYPE_BITS (time_t) <= LDBL_MANT_DIG || TYPE_FLOATING (time_t))
+    return (long double) time1 - (long double) time0;
+
+  /* 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)