Performance: no lazy_static or const fn

[sorpaas]

Right now as we build on stable Rust, const fn is not available. Thus struct like Gas are constructed on the fly (the config file only store a u64). Performance can be improved if we utilize lazy_static or const fn, if the latter ever stabilize (rust-lang/rust#24111).

[sorpaas]

Moved to https://github.com/ethereumproject/sputnikvm/wiki/Performance-Improvements due to #175.

[sorpaas]

lazy_static deps is now used in the core sputnikvm crate.

[zjhmale]

@sorpaas So all these precompiled gas functions need to be utilized with lazy_static right?

[sorpaas]

Actually originally this was related to all const variables here (https://github.com/ethereumproject/sputnikvm/blob/master/src/eval/cost.rs#L9). Because Gas needs to be constructed on the fly and it's not free, it might be a performance issue. (See all the Into::into() below.)

Still, however, I just realized that Gas implements Copy trait, so even if when it is lazy-static-ed it might still not help a lot. A constraint on the Ethereum blockchain is that Gas, although its theoretical max value is U256::max_value(), it in practice cannot exceed usize::max_value(). A better way to handle this is probably to make Gas a type parameter in all VM structs. After that, track the initial provided gas, if that value exceeds usize::max_value(), use usize as the type parameter, otherwise, fallback to the full U256 (the conditional check does not need to be in the sputnikvm library).

The type parameter of gas G usually only needs Add + Mul + Sub + From<usize>. In the calculation of memory cost, however, there needs to be a checked multiply which does not belong to a trait, so a custom trait might need to be created for that.

Oops sorry I probably should be more careful when labeling an issue as "good first issue".