Target FP: Introduce target-float.{c,h}

This patch introduces the new set of target floating-point handling routines
in target-float.{c,h}.  In the end, the intention is that this file will
contain support for all operations in target FP format, fully replacing
both the current doublest.{c,h} and dfp.{c,h}.

To begin with, this patch only adds a target_float_is_zero routine,
which handles the equivalent of decimal_is_zero for both binary and
decimal FP.  For the binary case, to avoid conversion to DOUBLEST,
this is implemented using the floatformat_classify routine.

However, it turns out that floatformat_classify actually has a bug
(it was not used to check for zero before), so this is fixed as well.

The new routine is used in both value_logical_not and valpy_nonzero.

There is one extra twist: the code previously used value_as_double
to convert to DOUBLEST and then compare against zero.  That routine
performs an extra task: it detects invalid floating-point values
and raises an error.  In any place where value_as_double is removed
in favor of some target-float.c routine, we need to replace that check.

To keep this check centralized in one place, I've added a new routine
is_floating_value, which returns a boolean determining whether a
value's type is floating point (binary or decimal), and if so, also
performs the validity check.  Since we need to check whether a value
is FP before calling any of the target-float routines anyway, this
seems a good place to add the check without much code size overhead.

In some places where we only want to check for floating-point types
and not perform a validity check (e.g. for the *output* of an operation),
we can use the new is_floating_type routine (in gdbarch) instead.

The validity check itself is done by a new target_float_is_valid
routine in target-float, encapsulating floatformat_is_valid.

ChangeLog:
2017-11-06  Ulrich Weigand  <uweigand@de.ibm.com>

	* Makefile.c (SFILES): Add target-float.c.
	(HFILES_NO_SRCDIR): Add target-float.h.
	(COMMON_OBS): Add target-float.o.
	* target-float.h: New file.
	* target-float.c: New file.

	* doublest.c (floatformat_classify): Fix detection of float_zero.

	* gdbtypes.c (is_floating_type): New function.
	* gdbtypes.h (is_floating_type): Add prototype.

	* value.c: Do not include "floatformat.h".
	(unpack_double): Use target_float_is_valid.
	(is_floating_value): New function.
	* value.h (is_floating_value): Add prototype-

	* valarith.c: Include "target-float.h".
	(value_logical_not): Use target_float_is_zero.

	* python/py-value.c: Include "target-float.h".
	(valpy_nonzero): Use target_float_is_zero.

1 files changed, 62 insertions, 0 deletions

diff --git a/gdb/target-float.c b/gdb/target-float.c
new file mode 100644
index 0000000..a082b9c
--- /dev/null
+++ b/gdb/target-float.c
@@ -0,0 +1,62 @@
+/* Floating point routines for GDB, the GNU debugger.
+
+   Copyright (C) 2017 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "defs.h"
+#include "dfp.h"
+#include "doublest.h"
+#include "gdbtypes.h"
+#include "floatformat.h"
+#include "target-float.h"
+
+
+/* Typed floating-point routines.  These routines operate on floating-point
+   values in target format, represented by a byte buffer interpreted as a
+   "struct type", which may be either a binary or decimal floating-point
+   type (TYPE_CODE_FLT or TYPE_CODE_DECFLOAT).  */
+
+/* Return whether the byte-stream ADDR holds a valid value of
+   floating-point type TYPE.  */
+bool
+target_float_is_valid (const gdb_byte *addr, const struct type *type)
+{
+  if (TYPE_CODE (type) == TYPE_CODE_FLT)
+    return floatformat_is_valid (floatformat_from_type (type), addr);
+
+  if (TYPE_CODE (type) == TYPE_CODE_DECFLOAT)
+    return true;
+
+  gdb_assert_not_reached ("unexpected type code");
+}
+
+/* Return whether the byte-stream ADDR, interpreted as floating-point
+   type TYPE, is numerically equal to zero (of either sign).  */
+bool
+target_float_is_zero (const gdb_byte *addr, const struct type *type)
+{
+  if (TYPE_CODE (type) == TYPE_CODE_FLT)
+    return (floatformat_classify (floatformat_from_type (type), addr)
+	    == float_zero);
+
+  if (TYPE_CODE (type) == TYPE_CODE_DECFLOAT)
+    return decimal_is_zero (addr, TYPE_LENGTH (type),
+			    gdbarch_byte_order (get_type_arch (type)));
+
+  gdb_assert_not_reached ("unexpected type code");
+}
+