Re: [PATCH] Introduce --enable-math-noprivate

[Joseph Myers <joseph@codesourcery.com>]

On Thu, 20 Sep 2018, Florian Weimer wrote:

> > Similarly the strtod_nan* dependency seems worthwhile to remove too.
> 
> I haven't thought about this.  It's certainly a bit of a code
> duplication.
> 
> Joseph, any thoughts on that?

Well, sharing the implementation of NaN parsing between the nan functions 
and the strto* functions seemed to make sense (the old approach of the nan 
functions calling strto* having had problems as discussed in bugs 16961 
and 16962).  And to share it at the binary level, not just the source 
level, meant GLIBC_PRIVATE exports.  Since such exports are completely 
normal as the way for one glibc library to use internal functionality from 
another, I see no obvious reason to avoid using them by default, as 
opposed to with non-default configure options like this one.

There's potential for the functions to get more complicated in the 
_Float128 / binary128 long double case - the present approach is unable to 
represent NaN significand bits outside the trailing 64 (and fixing that 
would mean having something like strtoull that handles integers up to at 
least 111 bits - in which case either that something would need exporting 
from libc as public, or it would need exporting as GLIBC_PRIVATE and 
duplicating with the new option).  (You can construct NaNs with arbitrary 
payloads using setpayload functions, but having the nan/strto functions be 
able to do so as well would seem natural.)

-- 
Joseph S. Myers
joseph@codesourcery.com