Re: [PATCH v2] powerpc: Update ULPs and output for j0 with ibm128

[Joseph Myers <joseph@codesourcery.com>]

On Thu, 10 Sep 2020, Tulio Magno Quites Machado Filho via Libc-alpha wrote:

> Carlos, Joseph,
> 
> I'm afraid that Matheus is either in a deadlock or we need a clearer
> explanation of what is acceptable for ibm128.
> 
> Notice that Matheus' first patch was rejected because results were greater
> than 9.
> 
> With that said, would both of you accept the first version of this patch?
> https://patchwork.sourceware.org/project/glibc/patch/20200820183700.115087-1-msc@linux.ibm.com/

The first version is appropriate.  The bigger limits for ibm128 are 
deliberate.  An architecture-specific ulps update should not be rejected 
just because it increases ulps within the bounds accepted for that format 
(and you shouldn't be able to get an update that increases them outside 
those bounds unless you edit the ulps file manually, and if you do edit it 
manually then the ulps it lists outside those bounds will be ignored 
anyway).

The most likely reason for rejecting an ulps update is that new ulps are 
greater than for other architectures using the same code in glibc for the 
same functions for the same format, suggesting that the update is actually 
covering up a bug somewhere else.  This doesn't apply in this case.

(If an ulps increase results from a change to the implementation of a libm 
functions that makes it less accurate in some cases, we need to consider 
if we want that change, but that's deciding whether we want the libm 
change, not deciding whether we want the ulps updates consequent on it.)

-- 
Joseph S. Myers
joseph@codesourcery.com