Re: [PATCH] Add set/get functions for negative infinity in real.*

[Aldy Hernandez <aldyh@redhat.com>]

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On Fri, Aug 26, 2022 at 6:08 PM Jeff Law via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
>
>
> On 8/23/2022 4:33 AM, Aldy Hernandez via Gcc-patches wrote:
> > For the frange implementation with endpoints I'm about to contribute,
> > we need to set REAL_VALUE_TYPEs with negative infinity.  The support
> > is already there in real.cc, but it is awkward to get at.  One could
> > call real_inf() and then negate the value, but I've added the ability
> > to pass the sign argument like many of the existing real.* functions.
> >
> > I've declared the functions in such a way to avoid changes to the
> > existing code base:
> >
> > // Unchanged function returning true for either +-INF.
> > bool real_isinf (const REAL_VALUE_TYPE *r);
> > // New overload to be able to specify the sign.
> > bool real_isinf (const REAL_VALUE_TYPE *r, int sign);
> > // Replacement function for setting INF, defaults to +INF.
> > void real_inf (REAL_VALUE_TYPE *, int sign = 0);
> >
> > Tested on x86-64 Linux.
> >
> > OK?
> >
> > gcc/ChangeLog:
> >
> >       * real.cc (real_isinf): New overload.
> >       (real_inf): Add sign argument.
> >       * real.h (real_isinf): New overload.
> >       (real_inf): Add sign argument.
>
> Funny in that I've fairly recently had the desire to do something a bit
> similar.  Let's consider 0.5, which we have a dconsthalf, but we don't
> have dconstmhalf for -0.5.  To get that value I create a dconsthalf
> object and flip its sign.  Similarly for a variety of other special
> constants (particularly powers of two, but a few others as well).

Ugh, yeah.  I've been doing a lot of gymnastics in this space because
frange's will have REAL_VALUE_TYPE endpoints.

>
> Consider making the "sign" argument a boolean.  It's defined as a single
> bit bitfield in the real_value structure.   We don't want folks to pass
> in values outside [0..1] for the sign if we can easily avoid it:-)

I was trying to follow all the other functions in real.cc which have
"int sign", though I suppose none of them are exported in the header
file.

OK pending tests?
Aldy

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From 86664496f62f5d4d33da0347f5d5c017bd204513 Mon Sep 17 00:00:00 2001
From: Aldy Hernandez <aldyh@redhat.com>
Date: Sat, 20 Aug 2022 12:41:53 +0200
Subject: [PATCH] Add set/get functions for negative infinity in real.*

For the frange implementation with endpoints I'm about to contribute,
we need to set REAL_VALUE_TYPEs with negative infinity.  The support
is already there in real.cc, but it is awkward to get at.  One could
call real_inf() and then negate the value, but I've added the ability
to pass the sign argument like many of the existing real.* functions.

I've declared the functions in such a way to avoid changes to the
existing code base:

// Unchanged function returning true for either +-INF.
bool real_isinf (const REAL_VALUE_TYPE *r);
// New overload to be able to specify the sign.
bool real_isinf (const REAL_VALUE_TYPE *r, int sign);
// Replacement function for setting INF, defaults to +INF.
void real_inf (REAL_VALUE_TYPE *, int sign = 0);

gcc/ChangeLog:

	* real.cc (real_isinf): New overload.
	(real_inf): Add sign argument.
	* real.h (real_isinf): New overload.
	(real_inf): Add sign argument.
---
 gcc/real.cc | 14 +++++++++++---
 gcc/real.h  |  5 ++++-
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/gcc/real.cc b/gcc/real.cc
index 4e63b1449c5..dcf41b79f60 100644
--- a/gcc/real.cc
+++ b/gcc/real.cc
@@ -1234,6 +1234,14 @@ real_isinf (const REAL_VALUE_TYPE *r)
   return (r->cl == rvc_inf);
 }
 
+/* Determine whether a floating-point value X is infinite with SIGN.  */
+
+bool
+real_isinf (const REAL_VALUE_TYPE *r, bool sign)
+{
+  return real_isinf (r) && r->sign == sign;
+}
+
 /* Determine whether a floating-point value X is a NaN.  */
 
 bool
@@ -2484,12 +2492,12 @@ dconst_sqrt2_ptr (void)
   return &value;
 }
 
-/* Fills R with +Inf.  */
+/* Fills R with Inf with SIGN.  */
 
 void
-real_inf (REAL_VALUE_TYPE *r)
+real_inf (REAL_VALUE_TYPE *r, bool sign)
 {
-  get_inf (r, 0);
+  get_inf (r, sign);
 }
 
 /* Fills R with a NaN whose significand is described by STR.  If QUIET,
diff --git a/gcc/real.h b/gcc/real.h
index 845ef29e3a4..e01f9ed7282 100644
--- a/gcc/real.h
+++ b/gcc/real.h
@@ -277,6 +277,9 @@ extern bool real_compare (int, const REAL_VALUE_TYPE *, const REAL_VALUE_TYPE *)
 /* Determine whether a floating-point value X is infinite.  */
 extern bool real_isinf (const REAL_VALUE_TYPE *);
 
+/* Determine whether a floating-point value X is infinite with SIGN.  */
+extern bool real_isinf (const REAL_VALUE_TYPE *, bool sign);
+
 /* Determine whether a floating-point value X is a NaN.  */
 extern bool real_isnan (const REAL_VALUE_TYPE *);
 
@@ -331,7 +334,7 @@ extern long real_to_target (long *, const REAL_VALUE_TYPE *, format_helper);
 extern void real_from_target (REAL_VALUE_TYPE *, const long *,
 			      format_helper);
 
-extern void real_inf (REAL_VALUE_TYPE *);
+extern void real_inf (REAL_VALUE_TYPE *, bool sign = false);
 
 extern bool real_nan (REAL_VALUE_TYPE *, const char *, int, format_helper);
 
-- 
2.37.1