Exposing limb type choice by introducing _ZL and _ZLL

[itzmeanjan]

Hello Niek, first of all thanks for writing ctbignum -- such a great and useful library.

I'm using ctbignum for writing code, which I'm offloading to GPU. I noticed when converting literal input to std::integer_sequence, default limb type choice is uint64_t, which is somewhat problematic to me. As I was trying to target SPIRV, which not supporting __uint128_t so I was getting errors when writing GPU kernels which were performing modular multiplication.

Also I noticed your question

I've introduced _ZL and _ZLL -- these two new literal suffixes, while deprecating _Z. I'd love to know your opinion/ suggestion.

Thanks :)

Suffix	Note
_ZL	uint32_t as limb type
_ZLL	uint64_t as limb type
_Z	uint64_t ( as it is ) as limb type [ deprecated ]

[niekbouman]

Dear Anjan,

Thanks for your comments and the PR!

I've introduced _ZL and _ZLL -- these two new literal suffixes, while deprecating _Z. I'd love to know your opinion/ suggestion.

I'd like to keep _Z for compatibility reasons (ctbignum is being used in production ;-)
and 'L' and 'LL' sound like long and long long, while the limb types are unsigned.
How about, respectively, _Z32 and _Z64 ?

Another idea is to define a generalized literal, that people can "tailor" to their limb type by means of a using declaration:

// in library 
template <typename limb_t, char... Chars> 
constexpr auto operator"" _generic_limb_literal(); 

// in user code
template<char... Chars>
using _Z16 = _generic_limb_literal<uint16_t, Chars...>;

What would you think of that?

(BTW I'll also reply to your email later today)

[itzmeanjan]

Hello Niek,

ctbignum is being used in production

This is great news !

What would you think of that?

I find your solution to be sound and easier to understand. In user code when someone reads _Z{16,32,64}, they should get a feeling that limb type/ size is what is being denoted by suffixed number.

[niekbouman]

I've added something in spirit of the above in d5bde6d

Please check whether this works for you,

best,
Niek

[itzmeanjan]

Perfect thanks Niek, it works for me !