Test File: sc/qa/unit/data/functions/fods/chiinv.fods: fails with Assertion

[Alex McMurchy]

I shall give this a whirl.

Stephan Bergmann wrote

> Turns out, the relevant GCC switches are
>
>   -mfpmath=sse -msse2

Alex

On 16/09/16 11:05, Stephan Bergmann wrote:
> On 09/07/2016 10:37 PM, Eike Rathke wrote:
>> You could do us a favour, are you willing to invest some machine time
>> and try if passing either -msse or -msse2 as compiler flags would solve
>> the failing function tests problem? For this you'd need to do
>>
>> make clean
>> make ENVCFLAGS=-msse ENVCFLAGSCXX=-msse && make sc.check
>>
>> and if that still fails try
>>
>> make clean
>> make ENVCFLAGS=-msse2 ENVCFLAGSCXX=-msse2 && make sc.check
>
> Turns out, the relevant GCC switches are
>
>   -mfpmath=sse -msse2
>
> -mfpmath=sse (instead of the x86-32 default of -mfpmath=387) prevents 
> usage of the extended 80-bit precision for temporary results. (Which 
> caused e.g. the subtraction in ScChiDistFunction::GetValue, 
> sc/source/core/tool/interpr3.cxx, to produce results different from 
> IEEE double, causing the computation of CHIINV(0.999999999999999, 
> 1.00000000000000E+001) in sc/qa/unit/data/functions/fods/chiinv.fods 
> to produce unexpected results.) 
> <https://gcc.gnu.org/onlinedocs/gcc-6.2.0/gcc/x86-Options.html#x86-Options> 
> also claims: "The resulting code should be considerably faster 
> [compared to -mfpmath=387] in the majority of cases and avoid the 
> numerical instability problems of 387 code [...]"
>
> But -mfpmath=sse only takes effect when compiling for an architecture 
> that actually supports the relevant SSE instructions (otherwise 
> silently falling back to the "387" instructions, it appears).  So we 
> need an additional -msse2 to enable the instructions relevant for 
> 64-bit double (-msse would only enable instructions relevant for 
> 32-bit float).
>
> SSE2 support reportedly got added with Pentium 4, around 2001. Any 
> thoughts on whether we'd want to enforce that for 32-bit x86 Linux 
> builds (or already effectively enforce anyway)?  In which case we 
> could add the relevant flags to 
> solenv/gbuild/platform/LINUX_INTEL_GCC.mk and revert 
> <https://cgit.freedesktop.org/libreoffice/core/commit/?id=b9a27d5856f60688456762bfcc29c38670009254> 
> "sc: disable function test documents for 32-bit PLATFORMID=linux_x86" 
> again.
>
> (Notwithstanding the fact that tests that rely on Calc doing 
> computations in a specific way, when Calc doesn't give any guarantees 
> of how those computations should be carried out exactly AFAIK, are 
> dubious and a pain at best.)
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