Re: [RFC PATCH v2] target/ppc: Enable hardfloat for PPC

[Programmingkid]

> On Feb 26, 2020, at 12:27 PM, Aleksandar Markovic <address@hidden> wrote:
> 
> On Wed, Feb 26, 2020 at 6:04 PM G 3 <address@hidden> wrote:
>> 
>> Accuracy is an important part of the IEEE 754 floating point standard. The 
>> whole purpose of this standard is to ensure floating point calculations are 
>> consistent across multiple CPUs. I believe referring to this patch as 
>> inaccurate is itself inaccurate. That gives the impression that this patch 
>> produces calculations that are not inline with established standards. This 
>> is not true. The only part of this patch that will produce incorrect values 
>> are the flags. There *may* be a program or two out there that depend on 
>> these flags, but for the majority of programs that only care about basic 
>> floating point arithmetic this patch will produce correct values. Currently 
>> the emulated PowerPC's FPU already produces wrong values for the flags. This 
>> patch does set the Inexact flag (which I don't like), but since I have never 
>> encountered any source code that cares for this flag, I can let it go. I 
>> think giving the user the ability to decide which option to use is the best 
>> thing to do.
>> 
> 
> From the experiments described above, the patch in question changes the 
> behavior
> of applications (for example, sound is different with and without the
> patch), which is
> in contradiction with your claim that you "never encountered any
> source code that
> cares for this flag" and that "the only part of this patch that will
> produce incorrect
> values are the flags".
> 
> In other words, and playing further with them:
> 
> The claim that "referring to this patch as inaccurate is itself
> inaccurate" is itself inaccurate.
> 
> Best regards,
> Aleksandar

It is inaccurate to state that just because the USB audio device seems to play 
better with the hardfloat feature enabled that this changes the fact that I 
have yet to see any source code that actually reviews the flags. I have 
reviewed both the USB audio device and Apple's AppleUSBAudio class code and 
have not seen any mention of the exception flags.