Re: Seeking Endorsement: Boost.int128

Am 29.04.26 um 00:51 schrieb Matt Borland via Boost:
>> I have doubts regarding the signed/unsigned comparison behavior
>> deviation described here:
>>
>> https://develop.int128.cpp.al/uint128_t.html#uint128_t_sign_compare_behavior_deviation
>>
>> While I understand the reasons for wanting to implement comparison this
>> way, I thing I would rather prefer to keep the behavior consistent with
>> the rest of integer types. That is, make it the same as for built-in
>> integer types.
>
> It is the same behavior as the built-in types have when you set -Werror -Wsign-conversion -Wconversion which I think is uncontroversial to say is best practice. If this is behavior is removed from the library, then when a user does set the aforementioned flags they will not apply to mixed library type - builtin type operations which I think is the bigger risk. All of the analysis is static; there is zero runtime overhead introduced by these checks.
I'm a bit confused about the relation of "behavior" to warning flags.
My understanding of that would be that the library shows a compile-time 
error as it would with that warning flag(s) and Werror enabled.
Is that the case?

The docs however say:
 > With |uint128_t| we have checks even in this case like so:
 > ...
 > if(rhs >= 0) ... else return true;

This contradicts (my understanding of) the stated behavior to fail 
compilation on mixed comparison and also the "zero runtime overhead".

So what is it?

While I see how this behavior is less surprising for beginners, advanced 
users might rely on the wrap-around (mod 2^N) behavior.
Semi-contrived example: `operator[](signed_t idx) { if(size() > idx) 
return elements[idx]; }`

So I'd rather have this not compile (e.g. via static_assert) to be 
similar to the Werror case, than silently deviate from "standard behavior".

- Alex

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