[PATCH] math: Refactor how to use libm-test-ulps

[Paul Zimmermann]

       Dear Adhemerval,

> The constant libm-test-ulps shows little value, where it is usually a
> mechanical change done by the maintainer, for past releases it isi

it isi -> it is

> The manual error table is also removed, Paul Zimmermann has bee

has bee -> has been

> tracking libm precision with a more comprehensive analysis for some
> releases; so link to his work instead.
> +A more comprehensive analysis of @theglibc math function precision could
> +be found in 'Accuracy of Mathematical Functions in Single, Double, Double
> +Extended, and Quadruple Precision'; Brian Gladman, Vincenzo Innocente,
> +John Mather, and Paul Zimmermann at
> +@url{https://members.loria.fr/PZimmermann/papers/accuracy.pdf}

as Joseph pointed out, this analysis is only for x86_64, and for rounding to
nearest.

For complex functions, you might point to this (again for x86_64 and RNDN):

https://inria.hal.science/hal-04714173https://inria.hal.science/hal-04714173

> +A "libm-test-ulps" is required only to test for extra contraints in
> +the math tests.  The file contains lines for maximal errors of single
> +functions, like:
> +
> +Function "yn":
> +float: 2
> +double: 6
> +
> +It means that if the "yn" shows error larger than 2 ULP for float
> +or 3 ULP for double, the related test for "symbol" will fail.  It can

3 ULP -> 6 ULP

it might be useful to give an example with yn_upward (if supported)

Paul