Re: [PATCH 01/10] fpu: Make targets specify floatx80 default Inf at runtime

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 17/2/25 13:50, Peter Maydell wrote:
> Currently we hardcode at compile time whether the floatx80 default
> Infinity value has the explicit integer bit set or not (x86 sets it;
> m68k does not).  To be able to compile softfloat once for all targets
> we'd like to move this setting to runtime.
> 
> Define a new FloatX80Behaviour enum which is a set of flags that
> define the target's floatx80 handling.  Initially we define just one
> flag, for whether the default Infinity has the Integer bit set or
> not, but we will expand this in future commits to cover the other
> floatx80 target specifics that we currently make compile-time
> settings.
> 
> Define a new function floatx80_default_inf() which returns the
> appropriate default Infinity value of the given sign, and use it in
> the code that was previously directly using the compile-time constant
> floatx80_infinity_{low,high} values when packing an infinity into a
> floatx80.
> 
> Since floatx80 is highly unlikely to be supported in any new
> architecture, and the existing code is generally written as "default
> to like x87, with an ifdef for m68k", we make the default value for
> the floatx80 behaviour flags be "what x87 does".  This means we only
> need to change the m68k target to specify the behaviour flags.
> 
> (Other users of floatx80 are the Arm NWFPE emulation, which is
> obsolete and probably not actually doing the right thing anyway, and
> the PPC xsrqpxp insn.  Making the default be "like x87" avoids our
> needing to review and test for behaviour changes there.)
> 
> We will clean up the remaining uses of the floatx80_infinity global
> constant in subsequent commits.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>   include/fpu/softfloat-helpers.h | 12 ++++++++++++
>   include/fpu/softfloat-types.h   | 13 +++++++++++++
>   include/fpu/softfloat.h         |  1 +
>   fpu/softfloat.c                 |  7 +++----
>   target/m68k/cpu.c               |  6 ++++++
>   fpu/softfloat-specialize.c.inc  | 10 ++++++++++
>   6 files changed, 45 insertions(+), 4 deletions(-)


> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index f4fed9bfda9..b12ad2b42a9 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -1860,7 +1860,8 @@ static floatx80 floatx80_round_pack_canonical(FloatParts128 *p,
>   
>       case float_class_inf:
>           /* x86 and m68k differ in the setting of the integer bit. */
> -        frac = floatx80_infinity_low;
> +        frac = s->floatx80_behaviour & floatx80_default_inf_int_bit_is_zero ?
> +            0 : (1ULL << 63);

Indent off, otherwise:

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>