Re: quadmath as distinct library?

From: Matt Borland (matt_at_[hidden])
Date: 2023-04-12 11:11:30

> On Apr 11, 2023, at 8:09 PM, Gero Peterhoff via Boost <boost_at_[hidden]> wrote:
>
> Am 13.03.23 um 13:33 schrieb John Maddock via Boost:
>
>> On 13/03/2023 02:43, Gero Peterhoff via Boost wrote:
>>
>>> Hello,
>>> * problem description
>>> In boost::math::cstdfloat AND boost::multiprecision::float128 identical functions for __float128 (quadmath) are provided.
>>>
>>> This is unnecessary overhead. I think it would make sense to "pull out" the quadmath library as a distinct library. I did this once canonically, but it doesn't work yet because boost::math::cstdfloat/boost::multiprecision::float128 have to be adapted for this. This is a prototype where there is still a lot of work to be done. But the beginning is done.
>>
>> If you mean https://github.com/boostorg/multiprecision/blob/develop/include/boost/multiprecision/detail/float128_functions.hpp then it's a trivially small header, and spinning stuff out into a separate library has a significant maintenance overhead.
>
> I mean this canonically.
> Advantages:
> - For both compilers (gcc/intel) the functions/limits can be provided directly, without the mass #define/#undef function-macros.
> - Clean separation and/or Konsolidierugn of the __float128 types:
> a) gcc: __float128

GCC also provides support for __ibm128 on PowerPC platforms. We don’t have any support for it because there has been no demand signal.

> b) intel: Windows _Qaud -> __float128, !Windows -> __float128 (https://community.intel.com/t5/Intel-C-Compiler/C-Compiler-128-bit-floating-point/m-p/1216949)
> So there is only one type __float128.
> - Clean/mature standard functions can be provided for IO.

> Disadvantages:
> - One-time(!) effort to update dependent libs.

Boost.Multiprecision is already available without the rest of Boost: https://github.com/boostorg/multiprecision/releases so there isn’t much bloat in the way it can be consumed now. Chris Kormanyos and I have discussed writing a software implementation of binary128 that could be used cross platform. That would be more valuable as a separate library.

Matt