Patchwork fpu/softfloat.c: Return correctly signed values from uint64_to_float32

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Submitter Peter Maydell
Date Sept. 28, 2012, 3:17 p.m.
Message ID <1348845423-20085-1-git-send-email-peter.maydell@linaro.org>
Download mbox | patch
Permalink /patch/187799/
State New
Headers show

Comments

Peter Maydell - Sept. 28, 2012, 3:17 p.m.
The uint64_to_float32() conversion function was incorrectly always
returning numbers with the sign bit set (ie negative numbers). Correct
this so we return positive numbers instead.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
As far as I can see we use this function only in the three PPC SPE
insns efscfuf, efsctsf, efsctuf. It is therefore untested(!); if
anybody with PPC hw to test against could check the results of
those functions that would be cool.

 fpu/softfloat.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
Peter Maydell - Sept. 28, 2012, 3:42 p.m.
On 28 September 2012 16:17, Peter Maydell <peter.maydell@linaro.org> wrote:
> The uint64_to_float32() conversion function was incorrectly always
> returning numbers with the sign bit set (ie negative numbers). Correct
> this so we return positive numbers instead.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> As far as I can see we use this function only in the three PPC SPE
> insns efscfuf, efsctsf, efsctuf. It is therefore untested(!); if
> anybody with PPC hw to test against could check the results of
> those functions that would be cool.

...incidentally in two of those uses we're operating on a constant:
 tmp = uint64_to_float64(1ULL << 32, &env->vec_status);
and it would probably be better to use make_float64() instead.

-- PMM
Aurelien Jarno - Oct. 1, 2012, 4:56 p.m.
On Fri, Sep 28, 2012 at 04:17:03PM +0100, Peter Maydell wrote:
> The uint64_to_float32() conversion function was incorrectly always
> returning numbers with the sign bit set (ie negative numbers). Correct
> this so we return positive numbers instead.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> As far as I can see we use this function only in the three PPC SPE
> insns efscfuf, efsctsf, efsctuf. It is therefore untested(!); if
> anybody with PPC hw to test against could check the results of
> those functions that would be cool.
> 
>  fpu/softfloat.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index b29256a..91497e8 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -1238,7 +1238,7 @@ float32 uint64_to_float32( uint64 a STATUS_PARAM )
>      if ( a == 0 ) return float32_zero;
>      shiftCount = countLeadingZeros64( a ) - 40;
>      if ( 0 <= shiftCount ) {
> -        return packFloat32( 1 > 0, 0x95 - shiftCount, a<<shiftCount );
> +        return packFloat32(0, 0x95 - shiftCount, a<<shiftCount);
>      }
>      else {
>          shiftCount += 7;
> @@ -1248,7 +1248,7 @@ float32 uint64_to_float32( uint64 a STATUS_PARAM )
>          else {
>              a <<= shiftCount;
>          }
> -        return roundAndPackFloat32( 1 > 0, 0x9C - shiftCount, a STATUS_VAR );
> +        return roundAndPackFloat32(0, 0x9C - shiftCount, a STATUS_VAR);
>      }
>  }
>  

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Aurelien Jarno - Oct. 1, 2012, 4:59 p.m.
On Fri, Sep 28, 2012 at 04:42:16PM +0100, Peter Maydell wrote:
> On 28 September 2012 16:17, Peter Maydell <peter.maydell@linaro.org> wrote:
> > The uint64_to_float32() conversion function was incorrectly always
> > returning numbers with the sign bit set (ie negative numbers). Correct
> > this so we return positive numbers instead.
> >
> > Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> > ---
> > As far as I can see we use this function only in the three PPC SPE
> > insns efscfuf, efsctsf, efsctuf. It is therefore untested(!); if
> > anybody with PPC hw to test against could check the results of
> > those functions that would be cool.

SPE instructions are not common on the non-embedded world, as far as I
know it should be tested using the e500 CPU. That said I don't have a
kernel nor an image for such a machine. 

> ...incidentally in two of those uses we're operating on a constant:
>  tmp = uint64_to_float64(1ULL << 32, &env->vec_status);
> and it would probably be better to use make_float64() instead.
> 

Agreed.
Aurelien Jarno - Oct. 1, 2012, 8:12 p.m.
On Fri, Sep 28, 2012 at 04:17:03PM +0100, Peter Maydell wrote:
> The uint64_to_float32() conversion function was incorrectly always
> returning numbers with the sign bit set (ie negative numbers). Correct
> this so we return positive numbers instead.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> As far as I can see we use this function only in the three PPC SPE
> insns efscfuf, efsctsf, efsctuf. It is therefore untested(!); if
> anybody with PPC hw to test against could check the results of
> those functions that would be cool.
> 
>  fpu/softfloat.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index b29256a..91497e8 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -1238,7 +1238,7 @@ float32 uint64_to_float32( uint64 a STATUS_PARAM )
>      if ( a == 0 ) return float32_zero;
>      shiftCount = countLeadingZeros64( a ) - 40;
>      if ( 0 <= shiftCount ) {
> -        return packFloat32( 1 > 0, 0x95 - shiftCount, a<<shiftCount );
> +        return packFloat32(0, 0x95 - shiftCount, a<<shiftCount);
>      }
>      else {
>          shiftCount += 7;
> @@ -1248,7 +1248,7 @@ float32 uint64_to_float32( uint64 a STATUS_PARAM )
>          else {
>              a <<= shiftCount;
>          }
> -        return roundAndPackFloat32( 1 > 0, 0x9C - shiftCount, a STATUS_VAR );
> +        return roundAndPackFloat32(0, 0x9C - shiftCount, a STATUS_VAR);
>      }
>  }
>  

Thanks, applied.

Patch

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index b29256a..91497e8 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -1238,7 +1238,7 @@  float32 uint64_to_float32( uint64 a STATUS_PARAM )
     if ( a == 0 ) return float32_zero;
     shiftCount = countLeadingZeros64( a ) - 40;
     if ( 0 <= shiftCount ) {
-        return packFloat32( 1 > 0, 0x95 - shiftCount, a<<shiftCount );
+        return packFloat32(0, 0x95 - shiftCount, a<<shiftCount);
     }
     else {
         shiftCount += 7;
@@ -1248,7 +1248,7 @@  float32 uint64_to_float32( uint64 a STATUS_PARAM )
         else {
             a <<= shiftCount;
         }
-        return roundAndPackFloat32( 1 > 0, 0x9C - shiftCount, a STATUS_VAR );
+        return roundAndPackFloat32(0, 0x9C - shiftCount, a STATUS_VAR);
     }
 }