Ulrich Weigand
2017-09-05T18:21:48Z

[RFC][13/19] Target FP: Perform Ada fixed-point scaling in target format

One of the few still remaining uses of DOUBLEST in GDB is the Ada front-end
code that handles scaling of Ada fixed-point types. The target format for
those types is some integer format; to convert those values to standard
floating-point representation, that integer needs to be multiplied by a
rational scale factor, given as a pair of numerator and denominator.

To avoid having to deal with long integer arithmetic, the current Ada
front-end code currently performs those scaling operations in host
DOUBLEST arithmetic. To eliminate this use of DOUBLEST, this patch
changes the front-end to instead perform those operations in the
*target* floating-point format (chosing to use the target "long double").

The implementation is mostly straight-forward, using value_cast and
value_binop to perform the target operations.

Scanning in the scale numerator and denominator is now done into
a host "long long" instead of a DOUBLEST, which should be large
enough to hold all possible values. (Otherwise, this can be replaced
by target-format target_float_from_string operations as well.)

Printing fixed-point types and values should be completely unchanges,
using target_float_to_string with the same format strings as current code.

Bye,
Ulrich

ChangeLog:

* ada-lang.c (cast_to_fixed): Reimplement in target arithmetic.
(cast_to_fixed): Likewise.
(ada_scaling_type): New function.
(ada_delta): Return value instead of DOUBLEST. Perform target
arithmetic instead of host arithmetic.
(scaling_factor): Rename to ...
(ada_scaling_factor) ... this. Return value instead of DOUBLEST.
Perform target arithmetic instead of host arithmetic.
(ada_fixed_to_float): Remove.
(ada_float_to_fixed): Remove.
* ada-lang.h (ada_fixed_to_float): Remove.
(ada_float_to_fixed): Remove.
(ada_delta): Return value instead of DOUBLEST.
(ada_scaling_factor): Add prototype.

* ada-typeprint.c: Include "target-float.h".
(print_fixed_point_type): Perform target arithmetic instead of
host arithmetic.
* ada-valprint.c: Include "target-float.h".
(ada_val_print_num): Perform target arithmetic instead of
host arithmetic for fixed-point types.

Index: binutils-gdb/gdb/ada-lang.c
===================================================================
--- binutils-gdb.orig/gdb/ada-lang.c
+++ binutils-gdb/gdb/ada-lang.c
@@ -9566,33 +9566,29 @@ unwrap_value (struct value *val)
}

static struct value *
-cast_to_fixed (struct type *type, struct value *arg)
+cast_from_fixed (struct type *type, struct value *arg)
{
- LONGEST val;
-
- if (type == value_type (arg))
- return arg;
- else if (ada_is_fixed_point_type (value_type (arg)))
- val = ada_float_to_fixed (type,
- ada_fixed_to_float (value_type (arg),
- value_as_long (arg)));
- else
- {
- DOUBLEST argd = value_as_double (arg);
-
- val = ada_float_to_fixed (type, argd);
- }
+ struct value *scale = ada_scaling_factor (value_type (arg));
+ arg = value_cast (value_type (scale), arg);

- return value_from_longest (type, val);
+ arg = value_binop (arg, scale, BINOP_MUL);
+ return value_cast (type, arg);
}

static struct value *
-cast_from_fixed (struct type *type, struct value *arg)
+cast_to_fixed (struct type *type, struct value *arg)
{
- DOUBLEST val = ada_fixed_to_float (value_type (arg),
- value_as_long (arg));
+ if (type == value_type (arg))
+ return arg;
+
+ struct value *scale = ada_scaling_factor (type);
+ if (ada_is_fixed_point_type (value_type (arg)))
+ arg = cast_from_fixed (value_type (scale), arg);
+ else
+ arg = value_cast (value_type (scale), arg);

- return value_from_double (type, val);
+ arg = value_binop (arg, scale, BINOP_DIV);
+ return value_cast (type, arg);
}

/* Given two array types T1 and T2, return nonzero iff both arrays
@@ -11474,68 +11470,57 @@ ada_is_system_address_type (struct type
}

/* Assuming that TYPE is the representation of an Ada fixed-point
- type, return its delta, or -1 if the type is malformed and the
+ type, return the target floating-point type to be used to represent
+ of this type during internal computation. */
+
+static struct type *
+ada_scaling_type (struct type *type)
+{
+ return builtin_type (get_type_arch (type))->builtin_long_double;
+}
+
+/* Assuming that TYPE is the representation of an Ada fixed-point
+ type, return its delta, or NULL if the type is malformed and the
delta cannot be determined. */

-DOUBLEST
+struct value *
ada_delta (struct type *type)
{
const char *encoding = fixed_type_info (type);
- DOUBLEST num, den;
+ struct type *scale_type = ada_scaling_type (type);

- /* Strictly speaking, num and den are encoded as integer. However,
- they may not fit into a long, and they will have to be converted
- to DOUBLEST anyway. So scan them as DOUBLEST. */
- if (sscanf (encoding, "_%" DOUBLEST_SCAN_FORMAT "_%" DOUBLEST_SCAN_FORMAT,
- &num, &den) < 2)
- return -1.0;
+ long long num, den;
+
+ if (sscanf (encoding, "_%lld_%lld", &num, &den) < 2)
+ return nullptr;
else
- return num / den;
+ return value_binop (value_from_longest (scale_type, num),
+ value_from_longest (scale_type, den), BINOP_DIV);
}

/* Assuming that ada_is_fixed_point_type (TYPE), return the scaling
factor ('SMALL value) associated with the type. */

-static DOUBLEST
-scaling_factor (struct type *type)
+struct value *
+ada_scaling_factor (struct type *type)
{
const char *encoding = fixed_type_info (type);
- DOUBLEST num0, den0, num1, den1;
+ struct type *scale_type = ada_scaling_type (type);
+
+ long long num0, den0, num1, den1;
int n;

- /* Strictly speaking, num's and den's are encoded as integer. However,
- they may not fit into a long, and they will have to be converted
- to DOUBLEST anyway. So scan them as DOUBLEST. */
- n = sscanf (encoding,
- "_%" DOUBLEST_SCAN_FORMAT "_%" DOUBLEST_SCAN_FORMAT
- "_%" DOUBLEST_SCAN_FORMAT "_%" DOUBLEST_SCAN_FORMAT,
+ n = sscanf (encoding, "_%lld_%lld_%lld_%lld",
&num0, &den0, &num1, &den1);

if (n < 2)
- return 1.0;
+ return value_from_longest (scale_type, 1);
else if (n == 4)
- return num1 / den1;
+ return value_binop (value_from_longest (scale_type, num1),
+ value_from_longest (scale_type, den1), BINOP_DIV);
else
- return num0 / den0;
-}
-
-
-/* Assuming that X is the representation of a value of fixed-point
- type TYPE, return its floating-point equivalent. */
-
-DOUBLEST
-ada_fixed_to_float (struct type *type, LONGEST x)
-{
- return (DOUBLEST) x *scaling_factor (type);
-}
-
-/* The representation of a fixed-point value of type TYPE
- corresponding to the value X. */
-
-LONGEST
-ada_float_to_fixed (struct type *type, DOUBLEST x)
-{
- return (LONGEST) (x / scaling_factor (type) + 0.5);
+ return value_binop (value_from_longest (scale_type, num0),
+ value_from_longest (scale_type, den0), BINOP_DIV);
}

\f
Index: binutils-gdb/gdb/ada-lang.h
===================================================================
--- binutils-gdb.orig/gdb/ada-lang.h
+++ binutils-gdb/gdb/ada-lang.h
@@ -305,11 +305,9 @@ extern int ada_is_fixed_point_type (stru

extern int ada_is_system_address_type (struct type *);

-extern DOUBLEST ada_delta (struct type *);
+extern struct value *ada_delta (struct type *);

-extern DOUBLEST ada_fixed_to_float (struct type *, LONGEST);
-
-extern LONGEST ada_float_to_fixed (struct type *, DOUBLEST);
+extern struct value *ada_scaling_factor (struct type *);

extern struct type *ada_system_address_type (void);

Index: binutils-gdb/gdb/ada-typeprint.c
===================================================================
--- binutils-gdb.orig/gdb/ada-typeprint.c
+++ binutils-gdb/gdb/ada-typeprint.c
@@ -31,6 +31,7 @@
#include "demangle.h"
#include "c-lang.h"
#include "typeprint.h"
+#include "target-float.h"
#include "ada-lang.h"
#include <ctype.h>

@@ -360,16 +361,23 @@ print_enum_type (struct type *type, stru
static void
print_fixed_point_type (struct type *type, struct ui_file *stream)
{
- DOUBLEST delta = ada_delta (type);
- DOUBLEST small = ada_fixed_to_float (type, 1);
+ struct value *delta = ada_delta (type);
+ struct value *small = ada_scaling_factor (type);

- if (delta < 0.0)
+ if (delta == nullptr)
fprintf_filtered (stream, "delta ??");
else
{
- fprintf_filtered (stream, "delta %g", (double) delta);
- if (delta != small)
- fprintf_filtered (stream, " <'small = %g>", (double) small);
+ std::string str;
+ str = target_float_to_string (value_contents (delta),
+ value_type (delta), "%g");
+ fprintf_filtered (stream, "delta %s", str.c_str());
+ if (!value_equal (delta, small))
+ {
+ str = target_float_to_string (value_contents (small),
+ value_type (small), "%g");
+ fprintf_filtered (stream, " <'small = %s>", str.c_str());
+ }
}
}

Index: binutils-gdb/gdb/ada-valprint.c
===================================================================
--- binutils-gdb.orig/gdb/ada-valprint.c
+++ binutils-gdb/gdb/ada-valprint.c
@@ -31,6 +31,7 @@
#include "c-lang.h"
#include "infcall.h"
#include "objfiles.h"
+#include "target-float.h"

static int print_field_values (struct type *, const gdb_byte *,
int,
@@ -796,10 +797,15 @@ ada_val_print_num (struct type *type, co
{
if (ada_is_fixed_point_type (type))
{
- LONGEST v = unpack_long (type, valaddr + offset_aligned);
-
- fprintf_filtered (stream, TYPE_LENGTH (type) < 4 ? "%.11g" : "%.17g",
- (double) ada_fixed_to_float (type, v));
+ struct value *scale = ada_scaling_factor (type);
+ struct value *v = value_from_contents (type, valaddr + offset_aligned);
+ v = value_cast (value_type (scale), v);
+ v = value_binop (v, scale, BINOP_MUL);
+
+ const char *fmt = TYPE_LENGTH (type) < 4 ? "%.11g" : "%.17g";
+ std::string str
+ = target_float_to_string (value_contents (v), value_type (v), fmt);
+ fputs_filtered (str.c_str (), stream);
return;
}
else if (TYPE_CODE (type) == TYPE_CODE_RANGE)