Re: [PATCH,Fortran] Handle 'q' exponent-letter in real-literal-constant

[Steve Kargl <sgk at troutmask dot apl dot washington dot edu>]

On Mon, Apr 25, 2011 at 11:42:07AM -0700, Steve Kargl wrote:
> 
> 2011-04-25  Steven G. Kargl  <kargl@gcc.gnu.org.>
> 
> 	PR fortran/48720
> 	* gfortran.texi: Document the 'Q' exponent-letter extension.
> 	* primary.c (match_real_constant):  Accept 'Q' as exponent-letter
> 	for REAL(16) real-literal-constant with a fallback to REAL(10) or
> 	error if REAL(10) is not available.

Of course, it would be helpful to include the patch.

-- 
Steve

Index: gfortran.texi
===================================================================
--- gfortran.texi	(revision 172773)
+++ gfortran.texi	(working copy)
@@ -1237,6 +1237,7 @@ without warning.
 * Missing period in FORMAT specifications::
 * I/O item lists::
 * BOZ literal constants::
+* @code{Q} exponent-letter::
 * Real array indices::
 * Unary operators::
 * Implicitly convert LOGICAL and INTEGER values::
@@ -1427,6 +1428,23 @@ To support legacy codes, GNU Fortran all
 of the @code{READ} statement, and the output item lists of the
 @code{WRITE} and @code{PRINT} statements, to start with a comma.
 
+@node @code{Q} exponent-letter
+@subsection @code{Q} exponent-letter
+@cindex @code{Q} exponent-letter
+
+GNU Fortran accepts real literal constants with an exponent-letter
+of @code{Q}, for example, @code{1.23Q45}.  Prior to version 4.6.1,
+GNU Fortran silently accepted @code{Q} as an alias for the single
+precision exponent-letter @code{E}.  With the introduction of software
+support for @code{REAL(16)} (i.e., quadruple precision) on i386 and
+x86_64 targets, the interpretation of @code{Q} has been updated to
+mean a @code{REAL(16)} real-literal-constant.  This aligns GNU Fortran
+with many commercially available compilers.  If the target does not
+support @code{REAL(16)} but has a @code{REAL(10)} type, then the
+real-literal-constant will be interpreted as a @code{REAL(10)} entity.
+In the absence of @code{REAL(16)} and @code{REAL(10)}, an error will
+occur.
+
 @node BOZ literal constants
 @subsection BOZ literal constants
 @cindex BOZ literal constants
Index: primary.c
===================================================================
--- primary.c	(revision 172773)
+++ primary.c	(working copy)
@@ -541,6 +541,17 @@ match_real_constant (gfc_expr **result, 
     goto done;
   exp_char = c;
 
+
+  if (c == 'q')
+    {
+      if (gfc_notify_std (GFC_STD_GNU, "Extension: exponent-letter 'q' in "
+			 "real-literal-constant at %C") == FAILURE)
+	return MATCH_ERROR;
+      else
+	gfc_warning("Extension: exponent-letter 'q' in real-literal-constant "
+		    "at %C");
+    }
+
   /* Scan exponent.  */
   c = gfc_next_ascii_char ();
   count++;
@@ -616,6 +627,29 @@ done:
       kind = gfc_default_double_kind;
       break;
 
+    case 'q':
+      if (kind != -2)
+	{
+	  gfc_error ("Real number at %C has a 'q' exponent and an explicit "
+		     "kind");
+	  goto cleanup;
+	}
+
+      /* The maximum possible real kind type parameter is 16.  First, try
+	 that for the kind, then fallback to trying kind=10 (Intel 80 bit)
+	 extended precision.  If neither value works, just given up.  */
+      kind = 16;
+      if (gfc_validate_kind (BT_REAL, kind, true) < 0)
+	{
+	  kind = 10;
+          if (gfc_validate_kind (BT_REAL, kind, true) < 0)
+	    {
+	      gfc_error ("Invalid real kind %d at %C", kind);
+	      goto cleanup;
+	    }
+	}
+      break;
+
     default:
       if (kind == -2)
 	kind = gfc_default_real_kind;