fixed int128 implementation

[omotorin]

I found some bugs in implementation of int128. It related with LLVMConstInt that works only with 64 bit integer and 128 bit will always cut to 64 bit. Also I've implemented to_int128/to_uint128 that needed to correct works codegen for 128 bit integer

[RX14]

I'm concerned about all to_i calls having to go through 128bit mathematics: it probably slows down the conversion process on processors without 128bit maths support (i.e. most of them).

I think it's a good idea to duplicate this method, and have both to_u64_info and to_u128_info. This can probably be done quite easily without extra boilerplate with macros.

If only we had a benchmark suite :)

[omotorin]

Yes, I agree. Also two test are failed because I extend to_u64_info method to support 128 bit integer and now they works incorrect with 64 bit.
I will fix it.

[lbguilherme]

Remove the TODO above

[Sija]

Related to #5545

[asterite]

@omotorin Thank you for this!

Some things:

1. You should add specs to every functionality you add. There are currently no specs to parse 128 bit numbers.
2. You modify the lexer but that change alone isn't enough. Please add specs, though I guess it will be hard to get right (it's a very custom logic to parse numbers). Plus maybe it's not good to us 128 bit integers to parse every number in a program. I could tackle this later in a separate PR if it turns out to be hard.

[Sija]

@omotorin Are you willing to continue?

[straight-shoota]

Closing stale PR. Int128 support is tracked in #8373
Thank you anyways 👍