Re: [Qemu-devel] [RFC] target-ppc/fpu_helper.c: Use C99 code to speed up floating point unit

[Paolo Bonzini <pbonzini@redhat.com>]

On 03/12/2016 06:59, Programmingkid wrote:
> The floating point code used in fpu_helper.c can be sped up by using
> the IEEE 754 support added to the C99 standard. To test this code out
> simply set and unset the I_NEED_SPEED macro. The program to test out
> each version of the helper_fmadd() function is below the patch. It
> needs to be ran in the guest. The emulator to use is qemu-system-ppc.
> I used a Mac OS X guest, but the test program would compile on a
> Linux guest.
> 
> This patch does make the fused multiply-add instruction fmadd work
> faster and still give a correct result.
> 
> This documentation might be of help to those who want to learn more
> about C99's IEEE 754 support: 
> http://grouper.ieee.org/groups/754/meeting-materials/2001-07-18-c99.pdf

You're undoing what was done in 2007:

commit 76a66253e5e48f1744f689041c1c21cedcaff630
Author: j_mayer <j_mayer@c046a42c-6fe2-441c-8c8c-71466251a162>
Date:   Wed Mar 7 08:32:30 2007 +0000

    Great PowerPC emulation code resynchronisation and improvments:
...
    - Micro-operation fixes:
...
      * use softfloat routines for all floating-point operations

Paolo