[geos-devel] 3.9.0beta2

[Paul Ramsey]

> On Dec 4, 2020, at 1:10 PM, Paul Ramsey <pramsey at cleverelephant.ca> wrote:
> 
> 
>> On Dec 3, 2020, at 10:18 PM, Sebastiaan Couwenberg <sebastic at xs4all.nl> wrote:
>> 
>> On 12/3/20 12:17 AM, Paul Ramsey wrote:
>>> without any further ado, here's a beta2 release for your testing pleasure
>> 
>> testrunner fails on arm64, ppc64el, powerpc, ppc64, riscv64:
> 
> Have we ever passed? Perhaps I made a big mistake removing ttmath. 
> 
> Anyways, here's what I've learned today, testing on an AWS ARM64 server.
> 
> * Still no obvious reason why these platforms shouldn't just work, if they implement IEEE conforming operations on double.
> * There's something called FLT_EVAL_METHOD in <cfloat> which might indicate non-IEEE handling of double, but... my test server insists it is FLT_EVAL_METHOD == 0 "evaluate just to the range and precision of the type".
> 
> Wondering if there was a brutal hack-around, and noting that "long double" is increasingly a "thing", I took our DD class, and hacked out all the smarts and substituted long double implementations.
> 
> https://github.com/pramsey/geos/tree/dd-arm
> 
> Interestingly, this implementation passes all the geos::math::DD tests! The ARM64 long double appears to have a full 128bit implementation. Running the same thing on Intel x64 fails a number of tests. This is probably because the long double implementation on x64 has only 80 bits (according to the internet).
> 
> Does all this test passing mean that a direct use of long double will work on platforms that support it? Apparently not. The ARM build still fails on quite a few tests of varying sorts, just not on the DD tests.
> 
> 	 90 - unit-capi-GEOSVoronoiDiagram (Failed)
> 	140 -unit-linearref-LengthIndexedLine (Failed)
> 	208 - general-TestCentroid (Failed)
> 	260 - issue-issue-geos-275 (Failed)
> 	267 - issue-issue-geos-398 (Failed)
> 	349 - robust-TestOverlay-pg-list (Failed)
> 
> Where does this leave us? With a long research project on ARM64 to track down why these tests fail and/or why the DD implementation fails.

Since this was a finite set of test failures and I was wondering if these failures were "real" or "tiny", I started going through them and the Voronoi failures seemed to fall into the "tiny" category. There was/is clearly a double precision equality test in the code that is returning true on one platform and false on another, because the answers are very very similar.

When I moved onto unit-linearref-LengthIndexedLine test, there wasn't any good printed debugging, so I broke out the debugger, and I had to rebuild in Debug mode. Guess what:

  100% tests passed, 0 tests failed out of 364

Yep, with the hardware long double for precision and in debug mode every test passes. So the problems on ARM64 are even *more* awful to figure out. Something about the optimized release build is different enough to matter.

P.


> Should we still release? I think so. While ARM and other niche platforms are coming down the pike, it doesn't make sense to delay. GEOS isn't "broken" on those platforms so much as "not perfect".
> 
> P.
> 
>