Support for EVM pieces

[larryk85]

For EOS-EVM, it has been highlighted that having the following data types and functions would be beneficial.

uint128, uint256, efficient to and from hex functions, others may be added in the next few days.

[mikelik]

Currently uint128 is available in CDT as:
typedef unsigned __int128 uint128_t;

The task would be to write new uint128_t and benchmark it against existing __int128 and uint128 from https://github.com/chfast/intx/blob/master/include/intx/intx.hpp.

As for uint256 it is currently unavailable in CDT, so it has to be created and benchmarked.

Optionally benchmarked might be wide integers from boost multiprecision or https://github.com/abseil/abseil-cpp/blob/master/absl/numeric/int128.h

[mikelik]

Benchmark of uint128:
abseil vs GCC's builtin vs intx vs boost

https://github.com/mikelik/int128-benchmark

[mikelik]

Decision is to go with _BitInt(128) and _BitInt(256) which are supported by clang-16. BitInt is part of C23 standard.

[mikelik]

wide int to/from hex functions benchmark: https://github.com/mikelik/int128-benchmark/blob/main/hex.cpp

[mikelik]

https://github.com/mikelik/int128-benchmark
Added benchmark hex conversion. Added new functions with improved performance by 30%

Following hex conversion functions has been chosen as fastest:
https://github.com/AntelopeIO/cdt/blob/mikelik/bitint/libraries/eosiolib/core/eosio/hex_conversion.hpp

[mikelik]

This is blocked by #185

[mikelik]

If someone picks this issue up they can start off from branch: https://github.com/AntelopeIO/cdt/tree/mikelik/bitint

[ericpassmore]

no longer a performance blocker, will re-open later