Patchwork RFC/RFA: Allow targets to override the definition of FLOAT_BIT_ORDER_MISMATCH

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Submitter Nick Clifton
Date June 13, 2012, 9:44 a.m.
Message ID <87obona6mz.fsf@Gift.fritz.box>
Download mbox | patch
Permalink /patch/164599/
State New
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Comments

Nick Clifton - June 13, 2012, 9:44 a.m.
Hi Guys,

  The RX port currently has a problem with the software implementation
  of 64-bit doubles - the libgcc functions produce bogus results.  I
  tracked this down to this definition in libgcc/fp-bit.h:

    #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
    #define FLOAT_BIT_ORDER_MISMATCH
    #endif

  For the RX __BYTE_ORDER__ is __ORDER_LITTLE_ENDIAN__, but the bits in
  the doubles are in little endian order, so FLOAT_BIT_ORDER_MISMATCH
  should not be defined.

  I have produced a patch (see below) that fixes this problem for me by
  allowing the target to specify FLOAT_BIT_ORDER_MISMATCH explicitly, if
  it wants to.  This matches the old behaviour (in gcc 4.6 and earlier)
  before fp-bit.h was moved to the libgcc directory.  I suspect however
  that this may not be the correct solution, so I am asking for comments
  as to how the problem should be solved.  If my approach is correct
  however, then please may I apply the patch ?

Cheers
  Nick

libgcc/ChangeLog
2012-06-13  Nick Clifton  <nickc@redhat.com>

	* fp-bit.h (FLOAT_BIT_ORDER_MISMATCH): If
	LIBGCC2_FLOAT_BIT_ORDER_MISMATCH is defined then use this to
	determine if FLOAT_BIT_ORDER_MISMATCH should be defined.
        * config/rx/rx-lib.h (LIBGCC2_FLOAT_BIT_ORDER_MISMATCH): Define
	to false.

Patch

Index: libgcc/fp-bit.h
===================================================================
--- libgcc/fp-bit.h	(revision 188497)
+++ libgcc/fp-bit.h	(working copy)
@@ -129,9 +129,21 @@ 
 #define NO_DI_MODE
 #endif
 
+/* Allow the target the chance to specify whether
+   the bit order matches the byte order.  */
+#if defined LIBGCC2_FLOAT_BIT_ORDER_MISMATCH
+/* Evaluate the expression - it might be zero.  */
+#if LIBGCC2_FLOAT_BIT_ORDER_MISMATCH
+#define FLOAT_BIT_ORDER_MISMATCH
+#else
+#undef  FLOAT_BIT_ORDER_MISMATCH
+#endif
+#else
+/* Otherwise assume that the bits within a byte are in big endian order.  */
 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 #define FLOAT_BIT_ORDER_MISMATCH
 #endif
+#endif
 
 #if __BYTE_ORDER__ != __FLOAT_WORD_ORDER__
 #define FLOAT_WORD_ORDER_MISMATCH
Index: libgcc/config/rx/rx-lib.h
===================================================================
--- libgcc/config/rx/rx-lib.h	(revision 188497)
+++ libgcc/config/rx/rx-lib.h	(working copy)
@@ -1,5 +1,10 @@ 
-#ifndef __RX_64BIT_DOUBLES__
+#if   defined __RX_64BIT_DOUBLES__
+#undef FLOAT_ONLY
+#elif defined __RX_32BIT_DOUBLES__
 #define DF SF
 #define FLOAT_ONLY
+#else
+#error "RX double size not defined"
 #endif
 
+#define LIBGCC2_FLOAT_BIT_ORDER_MISMATCH 0