Target FP: Handle interfaces to scripting languages

The last remaing use for DOUBLEST is in the code that interfaces to the
scripting languages (Python and Guile).  The problem here is that we
expose interfaces to convert a GDB value to and from native values of
floating-point type in those languages, and those by definition use
the host floating-point format.

While we cannot completely eliminate conversions to/from the host
floating-point format here, we still need to get rid of the uses
of value_as_double / value_from_double, since those will go away.

This patch implements two new target-float.c routine:
 - target_float_to_host_double
 - target_float_from_host_double
which convert to/from a host "double".  Those should only ever be
used where a host "double" is mandated by an external interface.

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

	* target-float.c (floatformat_to_host_double): New function.
	(floatformat_from_host_double): Likewise.
	(target_float_to_host_double): Likewise.
	(target_float_from_host_double): Likewise.
	* target-float.h (target_float_to_host_double): Add prototype.
	(target_float_from_host_double): Likewise.

	* guile/scm-value.c: Include "target-float.h".
	(gdbscm_value_to_real): Use target_float_to_host_double.
	Handle integer source values via value_as_long.
	* guile/scm-math.c: Include "target-float.h".  Do not include
	"doublest.h", "dfp.h", and "expression.h".
	(vlscm_convert_typed_number): Use target_float_from_host_double.
	(vlscm_convert_number): Likewise.

	* python/py-value.c (valpy_float): Use target_float_to_host_double.
	(convert_value_from_python): Use target_float_from_host_double.

6 files changed, 124 insertions, 11 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index ad8e0297610..8f0432aed10 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,25 @@
 2017-11-06  Ulrich Weigand  <uweigand@de.ibm.com>
 
+	* target-float.c (floatformat_to_host_double): New function.
+	(floatformat_from_host_double): Likewise.
+	(target_float_to_host_double): Likewise.
+	(target_float_from_host_double): Likewise.
+	* target-float.h (target_float_to_host_double): Add prototype.
+	(target_float_from_host_double): Likewise.
+
+	* guile/scm-value.c: Include "target-float.h".
+	(gdbscm_value_to_real): Use target_float_to_host_double.
+	Handle integer source values via value_as_long.
+	* guile/scm-math.c: Include "target-float.h".  Do not include
+	"doublest.h", "dfp.h", and "expression.h".
+	(vlscm_convert_typed_number): Use target_float_from_host_double.
+	(vlscm_convert_number): Likewise.
+
+	* python/py-value.c (valpy_float): Use target_float_to_host_double.
+	(convert_value_from_python): Use target_float_from_host_double.
+
+2017-11-06  Ulrich Weigand  <uweigand@de.ibm.com>
+
 	* ada-lang.c (cast_to_fixed): Reimplement in target arithmetic.
 	(cast_from_fixed): Likewise.
 	(ada_scaling_type): New function.
diff --git a/gdb/guile/scm-math.c b/gdb/guile/scm-math.c
index c4dfe71f54e..ef27d6859d8 100644
--- a/gdb/guile/scm-math.c
+++ b/gdb/guile/scm-math.c
@@ -24,9 +24,7 @@
 #include "arch-utils.h"
 #include "charset.h"
 #include "cp-abi.h"
-#include "doublest.h" /* Needed by dfp.h.  */
-#include "expression.h" /* Needed by dfp.h.  */
-#include "dfp.h"
+#include "target-float.h"
 #include "symtab.h" /* Needed by language.h.  */
 #include "language.h"
 #include "valprint.h"
@@ -599,7 +597,13 @@ vlscm_convert_typed_number (const char *func_name, int obj_arg_pos, SCM obj,
 	}
     }
   else if (TYPE_CODE (type) == TYPE_CODE_FLT)
-    return value_from_double (type, scm_to_double (obj));
+    {
+      struct value *value = allocate_value (type);
+      target_float_from_host_double (value_contents_raw (value),
+				     value_type (value),
+				     scm_to_double (obj));
+      return value;
+    }
   else
     {
       *except_scmp = gdbscm_make_type_error (func_name, obj_arg_pos, obj,
@@ -679,7 +683,13 @@ vlscm_convert_number (const char *func_name, int obj_arg_pos, SCM obj,
 				   gdbscm_scm_to_ulongest (obj));
     }
   else if (scm_is_real (obj))
-    return value_from_double (bt->builtin_double, scm_to_double (obj));
+    {
+      struct value *value = allocate_value (bt->builtin_double);
+      target_float_from_host_double (value_contents_raw (value),
+				     value_type (value),
+				     scm_to_double (obj));
+      return value;
+    }
 
   *except_scmp = gdbscm_make_out_of_range_error (func_name, obj_arg_pos, obj,
 			_("value not a number representable on the target"));
diff --git a/gdb/guile/scm-value.c b/gdb/guile/scm-value.c
index 3732666a889..0cf75472a12 100644
--- a/gdb/guile/scm-value.c
+++ b/gdb/guile/scm-value.c
@@ -24,6 +24,7 @@
 #include "arch-utils.h"
 #include "charset.h"
 #include "cp-abi.h"
+#include "target-float.h"
 #include "infcall.h"
 #include "symtab.h" /* Needed by language.h.  */
 #include "language.h"
@@ -1019,7 +1020,8 @@ gdbscm_value_to_real (SCM self)
     = vlscm_get_value_smob_arg_unsafe (self, SCM_ARG1, FUNC_NAME);
   struct value *value = v_smob->value;
   struct type *type;
-  DOUBLEST d = 0;
+  double d = 0;
+  struct value *check = nullptr;
 
   type = value_type (value);
 
@@ -1038,7 +1040,22 @@ gdbscm_value_to_real (SCM self)
 
   TRY
     {
-      d = value_as_double (value);
+      if (is_floating_value (value))
+	{
+	  d = target_float_to_host_double (value_contents (value), type);
+	  check = allocate_value (type);
+	  target_float_from_host_double (value_contents_raw (check), type, d);
+	}
+      else if (TYPE_UNSIGNED (type))
+	{
+	  d = (ULONGEST) value_as_long (value);
+	  check = value_from_ulongest (type, (ULONGEST) d);
+	}
+      else
+	{
+	  d = value_as_long (value);
+	  check = value_from_longest (type, (LONGEST) d);
+	}
     }
   CATCH (except, RETURN_MASK_ALL)
     {
@@ -1047,7 +1064,7 @@ gdbscm_value_to_real (SCM self)
   END_CATCH
 
   /* TODO: Is there a better way to check if the value fits?  */
-  if (d != (double) d)
+  if (!value_equal (value, check))
     gdbscm_out_of_range_error (FUNC_NAME, SCM_ARG1, self,
 			       _("number can't be converted to a double"));
 
diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
index 16c765094a0..11f1fc978f6 100644
--- a/gdb/python/py-value.c
+++ b/gdb/python/py-value.c
@@ -1560,10 +1560,10 @@ valpy_float (PyObject *self)
     {
       type = check_typedef (type);
 
-      if (TYPE_CODE (type) != TYPE_CODE_FLT)
+      if (TYPE_CODE (type) != TYPE_CODE_FLT || !is_floating_value (value))
 	error (_("Cannot convert value to float."));
 
-      d = value_as_double (value);
+      d = target_float_to_host_double (value_contents (value), type);
     }
   CATCH (except, RETURN_MASK_ALL)
     {
@@ -1681,7 +1681,11 @@ convert_value_from_python (PyObject *obj)
 	  double d = PyFloat_AsDouble (obj);
 
 	  if (! PyErr_Occurred ())
-	    value = value_from_double (builtin_type_pyfloat, d);
+	    {
+	      value = allocate_value (builtin_type_pyfloat);
+	      target_float_from_host_double (value_contents_raw (value),
+					     value_type (value), d);
+	    }
 	}
       else if (gdbpy_is_string (obj))
 	{
diff --git a/gdb/target-float.c b/gdb/target-float.c
index ad04f8fb4a1..d2c1064bb3a 100644
--- a/gdb/target-float.c
+++ b/gdb/target-float.c
@@ -59,6 +59,27 @@ floatformat_from_ulongest (const struct floatformat *fmt, gdb_byte *addr,
   floatformat_from_doublest (fmt, &d, addr);
 }
 
+/* Convert the byte-stream ADDR, interpreted as floating-point format FMT,
+   to a floating-point value in the host "double" format.  */
+static double
+floatformat_to_host_double (const struct floatformat *fmt,
+			    const gdb_byte *addr)
+{
+  DOUBLEST d;
+  floatformat_to_doublest (fmt, addr, &d);
+  return (double) d;
+}
+
+/* Convert floating-point value VAL in the host "double" format to a target
+   floating-number of format FMT and store it as byte-stream ADDR.  */
+static void
+floatformat_from_host_double (const struct floatformat *fmt, gdb_byte *addr,
+			      double val)
+{
+  DOUBLEST d = (DOUBLEST) val;
+  floatformat_from_doublest (fmt, &d, addr);
+}
+
 /* Convert a floating-point number of format FROM_FMT from the target
    byte-stream FROM to a floating-point number of format TO_FMT, and
    store it to the target byte-stream TO.  */
@@ -299,6 +320,42 @@ target_float_from_ulongest (gdb_byte *addr, const struct type *type,
   gdb_assert_not_reached ("unexpected type code");
 }
 
+/* Convert the byte-stream ADDR, interpreted as floating-point type TYPE,
+   to a floating-point value in the host "double" format.  */
+double
+target_float_to_host_double (const gdb_byte *addr,
+			     const struct type *type)
+{
+  if (TYPE_CODE (type) == TYPE_CODE_FLT)
+    return floatformat_to_host_double (floatformat_from_type (type), addr);
+
+  /* We don't support conversions between target decimal floating-point
+     types and the host double type here.  */
+
+  gdb_assert_not_reached ("unexpected type code");
+}
+
+/* Convert floating-point value VAL in the host "double" format to a target
+   floating-number of type TYPE and store it as byte-stream ADDR.  */
+void
+target_float_from_host_double (gdb_byte *addr, const struct type *type,
+			       double val)
+{
+  /* Ensure possible padding bytes in the target buffer are zeroed out.  */
+  memset (addr, 0, TYPE_LENGTH (type));
+
+  if (TYPE_CODE (type) == TYPE_CODE_FLT)
+    {
+      floatformat_from_host_double (floatformat_from_type (type), addr, val);
+      return;
+    }
+
+  /* We don't support conversions between target decimal floating-point
+     types and the host double type here.  */
+
+  gdb_assert_not_reached ("unexpected type code");
+}
+
 /* Convert a floating-point number of type FROM_TYPE from the target
    byte-stream FROM to a floating-point number of type TO_TYPE, and
    store it to the target byte-stream TO.  */
diff --git a/gdb/target-float.h b/gdb/target-float.h
index 466dd1b5c85..4ac88efb261 100644
--- a/gdb/target-float.h
+++ b/gdb/target-float.h
@@ -42,6 +42,11 @@ extern void target_float_from_longest (gdb_byte *addr,
 extern void target_float_from_ulongest (gdb_byte *addr,
 					const struct type *type,
 					ULONGEST val);
+extern double target_float_to_host_double (const gdb_byte *addr,
+					   const struct type *type);
+extern void target_float_from_host_double (gdb_byte *addr,
+					   const struct type *type,
+					   double val);
 extern void target_float_convert (const gdb_byte *from,
 				  const struct type *from_type,
 				  gdb_byte *to, const struct type *to_type);