Re: [PATCH] Update powerpc libm-test-ulps

[Joseph Myers <joseph@codesourcery.com>]

On Mon, 31 Aug 2020, Tulio Magno Quites Machado Filho via Libc-alpha wrote:

> > 2. Do (1) only for entries that have ULPs higher than a threshold (say,
> > 9 or 16)?
> 
> Likewise, if we're able to keep maximum ULPs at 9 without marking too many tests
> as xfail'ed, that's better.
> Per the contents of sysdeps/powerpc/fpu/libm-test-ulps, this should be possible
> and would not need have a greater max_valid_error for inexact functions just
> for ibm128.

If the functions for different floating-point formats use similar 
algorithms, the error may be a multiple of the error for the basic 
arithmetic operations.  Since the basic arithmetic operations for 
ldbl-128ibm are less accurate than for IEEE formats, it seems reasonable 
to allow larger errors for libm functions for that format as well.

Ideally the errors would be smaller than they are for some functions with 
larger errors, but that might require algorithmic improvements.  The 
existing bounds of 9 or 16 ulps are empirical, based on what's seen with 
functions where the issue is simply the accumulation of lots of separate 
errors rather than algorithms with inherent numerical problems.

-- 
Joseph S. Myers
joseph@codesourcery.com