Re: [hatari-devel] Re: FPU update

[Andreas Grabher <andreas.grabher@xxxxxxxxxxxx>]

Am 21.01.2017 um 22:08 schrieb Toni Wilen <twilen@xxxxxxxxxx>:

>>>> Attached is screenshot that shows errors, what do they mean? (Is
>>>> it correct or incorrect value or something else?)
>>> 
>>> FSGLMUL and FSGLDIV error cause most likely is this (which is not 
>>> handled yet):
>>> 
>>> "The input operand mantissas truncate to single precision before
>>> the multiply operation" (from M68000PRM.pdf)
>>> 
>>> (How to emulate this correctly?)
>>> 
>> These SGL functions are quite weird. I wrote some special functions
>> assuming this: - The input values are truncated (not rounded) to
>> single precision mantissa (after normalization, if necessary) - The
>> output value is rounded to single precision mantissa with these
>> exceptions: - Output overflows: Infinity or biggest normal number
>> with extended mantissa - Output severely underflows: Zero or smallest
>> denormalized number with extended mantissa
>> 
>> Please try the appended patch, but be aware this is highly
>> experimental. I'll have a look at FNEG and FABS tomorrow. But on
>> first view this can only be caused by missing NaN handling in those
>> functions. Other than this these functions are quite simple.
> 
> I merged it quickly but now all FSGL tests return error, including
> FSGLDIV tests that did pass previously.
> 
> As usual, official documentation is mostly useless.. Perhaps real
> hardware tests are again needed?
> 
Yes, maybe. Or maybe it would help if we knew the input values and what is expected as an output. That might point us to the issue.
I noticed there is a little mistake from merging my previous code. In the function normalizeFloatx80Subnormal there is an extra line at the end of the function, that should have been removed.