Move VRGDA logic into a lib

[0xBeans]

PR for #12

Followed the design of https://github.com/transmissions11/libcompound - split Linear and Logistic into 2 libs.

[saucepoint]

I like the idea of immortalizing Linear and Logistic getTargetSaleTime into their own libraries

My initial approach to #12 was only creating a base VRGDALibrary. Wonder if we should do the same here, but I'll let @transmissions11 chime in

from #13

library VRGDALibrary {
    function getVRGDAPrice(int256 _targetPrice, int256 _decayConstant, int256 _timeDelta) internal pure returns (uint256) {
        unchecked {
            // prettier-ignore
            return uint256(wadMul(_targetPrice, wadExp(unsafeWadMul(_decayConstant,
                _timeDelta
            ))));
        }
    }
}

My initial thoughts with this is it becomes kind of verbose:

VRGDALibrary.getVRGDAPrice(..., LinearVRGDA.getTargetSaleTime(...))

[saucepoint]

might as well move this to a library, no? it's the same in LogisticVRGDA.sol

[transmissions11]

wait why close?

[transmissions11]

sorry my bad for not merging earlier

[0xBeans]

@transmissions11 was just cleaning up some loose ends on GH, thought maybe this wasn't what you wanted haha Should I reopen?

[transmissions11]

yes def, sorry i will clean this up asap and get it merged!

[0xBeans]

yes def, sorry i will clean this up asap and get it merged!

[nvonpentz]

Hi @transmissions11 @0xBeans, I'm working on a VRGDA project that needs this library in order to make our contract upgradeable. To that end, I rebased this branch so it is up-to-date with current master branch, except for the LogisticToLinear implementation since it was only added recently. I pushed that branch here https://github.com/transmissions11/VRGDAs/compare/master...nvonpentz:VRGDAs:library-rebase?expand=1.

When making the remaining changes to the LogisticToLinear implementation, I noticed the abstractions didn't fit as well, so I created a fresh branch with a different approach. You can see that here https://github.com/transmissions11/VRGDAs/compare/master...nvonpentz:VRGDAs:library?expand=1. The main differences are that it

• Creates one library instead of two, with only one getVRGDAPrice function (similar to master), and separate getTargetSaleTimeLinear and getTargetSaleTimeLogistic functions.
• Does not remove all the abstract classes. Instead, logic common between the different VRGDA types (i.e. the getVRGDAPrice function) is defined in an abstract VRDGA class that Linear, Logitistic, and LogisticToLinear inherit from. I implemented things such that the interfaces defined by the current abstract contracts on master are preserved.

If it's useful, I'm happy to open a PR for either, but I also want to be respectful of the work @0xBeans has done already. In this case I went ahead and implemented in order to unblock myself. Cheers!