Re: [Qemu-devel] [PATCH 2/4] softfloat: add float32_set_sign(), float32_infinity, float64_half, float64_256 and float64_512.

[Aurelien Jarno <aurelien@aurel32.net>]

On Sun, Feb 20, 2011 at 10:09:46PM +0000, Peter Maydell wrote:
> On 20 February 2011 21:52, Aurelien Jarno <aurelien@aurel32.net> wrote:
> > On Fri, Feb 18, 2011 at 03:49:15PM +0100, Christophe Lyon wrote:
> 
> >> +#define float64_half make_float64(0x3fe0000000000000LL)
> >> +#define float64_256 make_float64(0x4070000000000000LL)
> >> +#define float64_512 make_float64(0x4080000000000000LL)
> >>
> >>  /*----------------------------------------------------------------------------
> >>  | The pattern for a default generated double-precision NaN.
> >
> > While it's probably a good idea to define the commonly used values in
> > softfloat.h, I don't think we should have all the values used by the
> > different targets here. Infinity, one, half, two probably have their
> > place here, I don't think it's the case of 256 and 512. It should be
> > better to defined them at the target level.
> 
> Are you happy with targets just doing make_float*() on a
> bit pattern? I guess that's the most straightforward thing,

Yes, I think it is the way to go.

> although at the moment the target-arm code seems to prefer
>   float32 three = int32_to_float32(3, s);
> I don't care very much personally as long as we're not doing
> a runtime division to get a constant 0.5 :-)

Doing that at runtime is clearly not a good solution.

> Incidentally, if you're up for some target-mips cleanup:
> target-mips/op_helper.c:#define FLOAT_ONE32 make_float32(0x3f8 << 20)
> 
> could be using float32_one instead. (ditto for float64).

Yes, one is a really common value among target, and in my opinion we
should keep it in softfloat.h. I have a local patch that does this
cleanup and also moves the constant 2 to softfloat.h. I'll submit it one
day with other mips softfloat cleanup.

> > Also for consistency, I
> > think it's better to define these value for all float size, or at least
> > for all the common ones (32, 64, maybe 16).
> 
> I wouldn't bother with 16, only ARM uses that and only for
> conversions to other formats.
> 

That's true, so let's do it float 32 and 64.

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