Re: additional math-functions

From: John Maddock (jz.maddock_at_[hidden])
Date: 2022-08-13 08:12:37

On 10/08/2022 21:17, Gero Peterhoff via Boost wrote:
> Am 10.08.22 um 20:23 schrieb John Maddock via Boost:
>> On 10/08/2022 18:09, Gero Peterhoff via Boost wrote:
>>> Hello,
>>> I would like to add several missing math functions in boost or 
>>> specialize/overload existing ones for more types. 
>> Which functions?
> 1) scalar types
> - isdenormal

OK

> - trigonometric cot/sec/csc, acot/asec/acsc, acoth/asech/acsch, 
> acot2(like atan2) -> the problem is not the implementation as such, 
> but a standardized error handling
Yep, I have wondered about those in the past.
> - abs/div for unsigned types -> useful/need in templates
Yep.  I had to add an "unsigned_abs" function to multiprecision to 
handle generic abs calls.
> - inv
> - sgn (support nan/inf, ±0)
boost::math::sign should do what you want already.
> - rounding 
> https://en.wikipedia.org/wiki/Rounding#Comparison_of_approaches_for_rounding_to_an_integer
Almost a library in it's own right ;)Â  But OK.
>
> 2) std::complex
> - complete all std-functions for complex
> - complete all special-functions for complex

That's a heck of a lot of work - certainly to get them reliable.

Do you want to make a start with some PR's for the low-hanging fruit?

Best, John.

>
> for the future
>
> 3) complex types
> - dual numbers https://en.wikipedia.org/wiki/Dual_number
> - split-complex numbers 
> https://en.wikipedia.org/wiki/Split-complex_number
>
> 4) logic
> - a modern constexpr implementation for tribool -> bool3
> - bool4 https://en.wikipedia.org/wiki/Four-valued_logic
>
> Best, Gero
>
>>> These should be constexpr if possible.
>>>
>>> My problems with the concrete implementations are:
>>> - Which C++ standard to use C++11/14/17/20/23 ?
>>> - Should these be implemented in ccmath and math ?
>>> Â Â  a) ccmath requires C++17 (eg "if constexpr"), so it is not 
>>> possible to simply call the ccmath version in math, since math 
>>> requires C++11.
>>
>> Maybe, but we have announced a move to C++14, and in any case new 
>> additions can use whatever std version they require, as long as that 
>> requirement is documented and actually needed (ie not just using cool 
>> new features "just because").
>>
>> I do note however, that the constexpr function may not be as 
>> efficient *at runtime* as they could be due to the need not to use 
>> compiler intrinsics / std lib functions and such (so they should 
>> probably be marked as consteval in C++20).  So yes, possibly two 
>> versions.  But it depends what the functions are?
>>
>> Best, John.
>>
>>> Â Â  b) On the other hand, the math functions are already included in 
>>> the standard (since C++11), so it wouldn't be necessary to continue 
>>> to provide them (especially since they are not constexpr).
>>>
>>> Where and how exactly and with which C++ standard can I add the 
>>> functions ?
>>>
>>> thx
>>> Gero
>>>
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