Re: Not supporting all rounding modes

[Thomas Schwinge <thomas at codesourcery dot com>]

Hi!

On Tue, 29 May 2012 13:13:05 +0000, "Joseph S. Myers" <joseph@codesourcery.com> wrote:
> On Tue, 29 May 2012, Thomas Schwinge wrote:
> 
> > As far as I can tell, glibc is currently prepared to handle either no
> > rounding modes, or all four -- but SH-4A apparently only supports two.
> > Or am I missing some information?
> 
> It should support arbitrary subsets, though you may need to define 
> __FE_UNDEFINED to an invalid mode as done on Tile for libm-test.inc to 
> work.

Right.  That one is very new and had not yet been present in the tree I
was testing in.


Does this look reasonable (please test):

diff --git a/sysdeps/sh/sh4/fpu/bits/fenv.h b/sysdeps/sh/sh4/fpu/bits/fenv.h
index 38c303f..25e6567 100644
--- a/sysdeps/sh/sh4/fpu/bits/fenv.h
+++ b/sysdeps/sh/sh4/fpu/bits/fenv.h
@@ -39,19 +39,17 @@ enum
 #define FE_ALL_EXCEPT \
 	(FE_INEXACT | FE_DIVBYZERO | FE_UNDERFLOW | FE_OVERFLOW | FE_INVALID)
 
-/* The SH FPU supports all of the four defined rounding modes.  We
-   use again the bit positions in the FPU control word as the values
-   for the appropriate macros.  */
+/* The SH FPU supports two of the four defined rounding modes: round to nearest
+   and round to zero.  We use again the bit positions in the FPU control word
+   as the values for the appropriate macros.  */
 enum
   {
+    __FE_UNDEFINED = -1,
+
     FE_TONEAREST = 0x0,
 #define FE_TONEAREST	FE_TONEAREST
     FE_TOWARDZERO = 0x1,
 #define FE_TOWARDZERO	FE_TOWARDZERO
-    FE_UPWARD = 0x2,
-#define FE_UPWARD	FE_UPWARD
-    FE_DOWNWARD = 0x3
-#define FE_DOWNWARD	FE_DOWNWARD
   };
 
 
diff --git a/sysdeps/sh/sh4/fpu/fegetround.c b/sysdeps/sh/sh4/fpu/fegetround.c
index 7368383..adaeb8a 100644
--- a/sysdeps/sh/sh4/fpu/fegetround.c
+++ b/sysdeps/sh/sh4/fpu/fegetround.c
@@ -28,5 +28,5 @@ fegetround (void)
   /* Get control word.  */
   _FPU_GETCW (cw);
 
-  return cw & 0x3;
+  return cw & 0x1;
 }
diff --git a/sysdeps/sh/sh4/fpu/fesetround.c b/sysdeps/sh/sh4/fpu/fesetround.c
index 4edf9c5..1dbc339 100644
--- a/sysdeps/sh/sh4/fpu/fesetround.c
+++ b/sysdeps/sh/sh4/fpu/fesetround.c
@@ -25,7 +25,7 @@ fesetround (int round)
 {
   fpu_control_t cw;
 
-  if ((round & ~0x3) != 0)
+  if ((round & ~0x1) != 0)
     /* ROUND is no valid rounding mode.  */
     return 1;
 
@@ -33,7 +33,7 @@ fesetround (int round)
   _FPU_GETCW (cw);
 
   /* Set rounding bits.  */
-  cw &= ~0x3;
+  cw &= ~0x1;
   cw |= round;
   /* Set new state.  */
   _FPU_SETCW (cw);


GrÃÃe,
 Thomas

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