Re: [PATCH 4/9] ldbl-128ibm-compat: Add a generic significand() implementation

[Joseph Myers <joseph at codesourcery dot com>]

On Wed, 6 Jun 2018, Tulio Magno Quites Machado Filho wrote:

> Create a template for significand and reuse it in the ldbl-128ibm-compat 
> directory.

The following applies to both this patch and the scalb one: I don't think 
it makes sense to have a template that is, in fact, only used for one 
format.

If using a template for significand, I'd expect it to be used for all 
floating-point types / formats (removing the existing s_significand*.c 
etc. from math/ and sysdeps/ieee754/ldbl-opt/, listing it in 
gen-libm-calls instead of libm-calls).  The empty version in 
sysdeps/ieee754/float128 would still ensure nothing gets built for 
significand for float128 and you'd still have the s_significandf128.c you 
add in this patch (the ChangeLog entry seems wrong to mention 
s_significandl.c).  Using templates like that would mean the object files 
define excess aliases such as significandf32, but those aliases aren't in 
Versions files so they are harmless, not exported from libm.

Much the same would apply to e_scalb templates.  For w_scalb you'd need to 
treat the existing w_scalb*_compat templates like the other compat ones - 
that is, make their entire contents conditional on LIBM_SVID_COMPAT (so 
they don't get built for new targets or static linking at all), while the 
new w_scalb template would be listed in gen-libm-calls and not have any 
LIBM_SVID_COMPAT conditionals in it, and a new dummy 
sysdeps/ieee754/float128/w_scalbf128.c would ensure no code actually gets 
built from that template in the normal float128 case.  Given the general 
handling of finite aliases I'd expect a new __scalbf128_finite function 
export to be added to the Versions file for ldbl-128ibm-compat as well.

I would suggest that patches adding such templates and using them for 
existing formats without changing the ABI anywhere (a cleanup / 
refactoring of existing code) be separated from patches that actually add 
new ldbl-128ibm-compat symbols.

-- 
Joseph S. Myers
joseph@codesourcery.com