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Show HN: Floating point arithmetic types in C++ for any size and any base

(github.com)
67 points seg_fault | 8 comments | 18 Oct 24 17:42 UTC | HN request time: 0.198s | source | bottom

Since there is so much interest on HN in floats lately and their software implementations, I wanted to show mine. It has no use and is just for teaching me floats and C++. Give me your thoughts.
1. listeria ◴[21 Oct 24 20:27 UTC] No.41908198[source]▶
Consider dropping the specializations for the type traits, given that it's undefined behavior:

https://en.cppreference.com/w/cpp/types/is_fundamental

https://en.cppreference.com/w/cpp/types/is_floating_point

https://en.cppreference.com/w/cpp/types/is_arithmetic

https://en.cppreference.com/w/cpp/types/is_scalar

https://en.cppreference.com/w/cpp/types/is_object

replies(2): >>41908384 #>>41909333 #
2. seg_fault ◴[21 Oct 24 20:48 UTC] No.41908384[source]▶
I don't get what you mean. I thought they specify how the type can be used?
replies(2): >>41908617 #>>41908663 #
3. secondcoming ◴[21 Oct 24 21:19 UTC] No.41908617[source]▶
Technically, you're not supposed to add your own specialisations to the `std` namespace
replies(1): >>41908849 #
4. badmintonbaseba ◴[21 Oct 24 21:25 UTC] No.41908663[source]▶
The cppreference page says:

> If the program adds specializations for std::is_fundamental or std::is_fundamental_v, the behavior is undefined.

This is an oversimplification. The actual rule is https://eel.is/c++draft/library#namespace.std-2 .

> the specialization meets the standard library requirements for the original template.

For is_fundamental<YourClassType> it means that is_fundamental<YourClassType>::value must be false, as YourClassType is not a fundamental type, as defined in https://eel.is/c++draft/basic.fundamental#17 .

Some traits are just not designed to be customization points.

5. pmalynin ◴[21 Oct 24 21:45 UTC] No.41908849{3}[source]▶
In general this isn’t true (i guess it is in this specific context). For example I believe it’s totally expected to specialize std hash
replies(1): >>41909632 #
6. dataflow ◴[21 Oct 24 22:41 UTC] No.41909333[source]▶
Why is std::is_object even specialized here? Isn't it always true regardless?
7. tyleo ◴[21 Oct 24 23:30 UTC] No.41909632{4}[source]▶
I’ve also done this with hash… though given the footguns scattered about, I wouldn’t be surprised if it broke the spec.
replies(1): >>41911240 #
8. Conscat ◴[22 Oct 24 04:36 UTC] No.41911240{5}[source]▶
That is a completely intended way to use std::hash, along with a few other functions like std::tuple_size and std::tuple_element.