[PATCH] PARISC: Avoid undefined shift in cnv_float.h

[PATCH] PARISC: Avoid undefined shift in cnv_float.h

[John David Anglin]

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The attached change fixes a float conversion problem found running the
GCC testsuite with GCC configured with --with-arch=2.0.

Signed-off-by: John David Anglin <dave.anglin@bell.net>



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diff --git a/arch/parisc/math-emu/cnv_float.h b/arch/parisc/math-emu/cnv_float.h
index 9071e09..37299c7 100644
--- a/arch/parisc/math-emu/cnv_float.h
+++ b/arch/parisc/math-emu/cnv_float.h
@@ -347,16 +347,15 @@
     Sgl_isinexact_to_fix(sgl_value,exponent)
 
 #define Duint_from_sgl_mantissa(sgl_value,exponent,dresultA,dresultB)	\
-  {Sall(sgl_value) <<= SGL_EXP_LENGTH;  /*  left-justify  */		\
+  {unsigned int val = Sall(sgl_value) << SGL_EXP_LENGTH;		\
     if (exponent <= 31) {						\
     	Dintp1(dresultA) = 0;						\
-    	Dintp2(dresultB) = (unsigned)Sall(sgl_value) >> (31 - exponent); \
+    	Dintp2(dresultB) = val >> (31 - exponent);			\
     }									\
     else {								\
-    	Dintp1(dresultA) = Sall(sgl_value) >> (63 - exponent);		\
-    	Dintp2(dresultB) = Sall(sgl_value) << (exponent - 31);		\
+    	Dintp1(dresultA) = val >> (63 - exponent);			\
+    	Dintp2(dresultB) = exponent <= 62 ? val << (exponent - 31) : 0;	\
     }									\
-    Sall(sgl_value) >>= SGL_EXP_LENGTH;  /* return to original */	\
   }
 
 #define Duint_setzero(dresultA,dresultB) 	\

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--
John David Anglin	dave.anglin@bell.net

Re: [PATCH] PARISC: Avoid undefined shift in cnv_float.h

[James Bottomley]

On Sun, 2012-04-01 at 12:57 -0400, John David Anglin wrote:
> The attached change fixes a float conversion problem found running the
> GCC testsuite with GCC configured with --with-arch=2.0.

Could you describe the actual problem? (it helps enormously when people
look at the change logs a year later and try and work out what the
actual issue is).

Thanks,

James

Re: [PATCH] PARISC: Avoid undefined shift in cnv_float.h

[John David Anglin]

On 1-Apr-12, at 1:06 PM, James Bottomley wrote:

> On Sun, 2012-04-01 at 12:57 -0400, John David Anglin wrote:
>> The attached change fixes a float conversion problem found running  
>> the
>> GCC testsuite with GCC configured with --with-arch=2.0.
>
> Could you describe the actual problem? (it helps enormously when  
> people
> look at the change logs a year later and try and work out what the
> actual issue is).


The actual problem occurs for an exponent value of 63.  This is the  
maximum
exponent value that can be passed.  This causes a left shift by 32 in  
the else
hunk of the macro.  This causes undefined behavior and the wrong value  
is
returned for dresultB.  The fix is the check "exponent <= 62".  If the  
exponent
is 63, dresultB is set to 0.

The patch also optimizes the operation a bit by copying
"Sall(sgl_value) << SGL_EXP_LENGTH" to val, so that sgl_value is not  
modified.

Dave
--
John David Anglin	dave.anglin@bell.net