Re: [Qemu-devel] [PATCH v2 0/3] ARM/softfloat: support flushing denormals on input

[Aurelien Jarno]

On Thu, Jan 06, 2011 at 07:37:52PM +0000, Peter Maydell wrote:
> On ARM, the FPSCR FZ bit (which controls whether denormals should be
> flushed to zero) is supposed to cause this flushing to occur both
> when the output of a calculation is a denormal (already implemented in
> softfloat) and also when the input to a calculation is a denormal
> (not implemented, as noted by a FIXME comment).
> 
> This patchset adds the support to softfloat for flushing denormals on
> input. This is controlled using a new status flag to enable it (so that
> CPUs which only flush on output continue to work). There is a new
> exception status bit to indicate when input flushing has happened
> (because on ARM it is reported via a different FPSCR bit to that used
> when an output denormal is flushed to zero).
> 
> I have deliberately only implemented this for input float32 and
> float64 values because that is what ARM requires (on ARM float16
> inputs must not be flushed to zero and floatx80 and float128 are
> not used) so other changes would be totally untested code.
> 
> Existing CPUs should be unaffected as there is no behaviour change
> unless the mode is enabled.
> 
> (I suspect that MIPS should be able to use this to implement the
> FCSR FO bit if desired.)
> 
> Tested using random instruction generation for vadd/vsub/vmul/vdiv
> with the FPSCR FZ bit set.
> 
> The only change from v1 is that I have split the old patch 2/2
> into two parts, since it accidentally included a one-liner bugfix
> where we were setting the softfloat cumulative exception flags
> wrongly if the FPSCR was written to explicitly.
> 
> Peter Maydell (3):
>   softfloat: Implement flushing input denormals to zero
>   ARM: Set softfloat cumulative exc flags from correct FPSCR bits
>   ARM: wire up the softfloat flush_input_to_zero flag
> 
>  fpu/softfloat.c     |  104 
> ++++++++++++++++++++++++++++++++++++++++++++++++++-
>  fpu/softfloat.h     |   22 ++++++++++-
>  target-arm/helper.c |   10 ++++-
>  3 files changed, 131 insertions(+), 5 deletions(-)
> 
> 

Thanks, all 3 applied.

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net