Re: REAL(16) (was Re: [Patch, Fortran] Two minor tweaks for type-bound procedure parsing)

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

On Mon, Aug 25, 2008 at 11:50:16PM +0200, Dominique Dhumieres wrote:
> > REAL(16) needs to be done in software -- on x86, x86-64 -- as it is not
> > supported in hardware; if you want to use more than REAL(8) on x86,
> > x86-64 you can use REAL(10).  Or you use a system such as PowerPC which
> > supports REAL(16) in silicon.
> 
> As far as I can tell, the ifc implementation is a "real" one where the 
> full 128 bits are used to code the real number.  So far i did not have the 
> time to play with it.
> 
> Now concerning gfortran and since gcc requires gmp and mpfr, how difficult 
> (efficient) would it be to use these libraries to implement REAL(xxx)?
> 

Getting +, -, *, and / working is almost trivial.  The hard part is 
getting REAL(16) working in all the fun corners of the standard 
as well as getting IO working.  Here's a start where one may need
to distinguish between hardware FP and software emulation.


Index: gfortran.h
===================================================================
--- gfortran.h	(revision 139565)
+++ gfortran.h	(working copy)
@@ -1592,6 +1592,7 @@ typedef struct
   unsigned int c_float : 1;
   unsigned int c_double : 1;
   unsigned int c_long_double : 1;
+  unsigned int emulated : 1;
 }
 gfc_real_info;
 
Index: trans-types.c
===================================================================
--- trans-types.c	(revision 139565)
+++ trans-types.c	(working copy)
@@ -78,7 +78,7 @@ gfc_logical_info gfc_logical_kinds[MAX_I
 static GTY(()) tree gfc_integer_types[MAX_INT_KINDS + 1];
 static GTY(()) tree gfc_logical_types[MAX_INT_KINDS + 1];
 
-#define MAX_REAL_KINDS 5
+#define MAX_REAL_KINDS 6
 gfc_real_info gfc_real_kinds[MAX_REAL_KINDS + 1];
 static GTY(()) tree gfc_real_types[MAX_REAL_KINDS + 1];
 static GTY(()) tree gfc_complex_types[MAX_REAL_KINDS + 1];
@@ -371,6 +371,7 @@ gfc_init_kinds (void)
       gfc_real_kinds[r_index].digits = fmt->p;
       gfc_real_kinds[r_index].min_exponent = fmt->emin;
       gfc_real_kinds[r_index].max_exponent = fmt->emax;
+      gfc_real_kinds[r_index].emulated = 0;
       if (fmt->pnan < fmt->p)
 	/* This is an IBM extended double format (or the MIPS variant)
 	   made up of two IEEE doubles.  The value of the long double is
@@ -384,6 +385,17 @@ gfc_init_kinds (void)
       r_index += 1;
     }
 
+  /* Set up emulation of REAL(16).  */
+  if (saw_r16 == false)
+    {
+      gfc_real_kinds[r_index].kind = 16;
+      gfc_real_kinds[r_index].radix = 2;
+      gfc_real_kinds[r_index].digits = 113;
+      gfc_real_kinds[r_index].min_exponent = -16382;
+      gfc_real_kinds[r_index].max_exponent = 16383;
+      gfc_real_kinds[r_index].emulated = 1;
+    }
+
   /* Choose the default integer kind.  We choose 4 unless the user
      directs us otherwise.  */
   if (gfc_option.flag_default_integer)
   
-- 
Steve