[Hackathon] Blake2b f compression precompile

[iikirilov]

PR description

Introduces the Blake2b F compression function as a precompile in Pantheon as specified in ethereum/EIPs#2129

Using the test vectors from https://github.com/keep-network/go-ethereum/blob/f-precompile/core/vm/contracts_test.go#L350

Implementation of Blake2b F compression function ported from https://github.com/keep-network/blake2 (BSD license)

Fixed Issue(s)

Consensys/protocol-BountiedWork#19

[shemnon]

Looks reasonable so far.

[iikirilov]

This PR has passed the deadline for the hackathon period but it is still incomplete.

1. The precompile was not integrated with the precompile registry.
2. The EIP has not been finalized so some implementation details/test vectors may change.
3. The gas calculation was not tested.
4. The name of the precompile was not agreed.

I have the capacity to follow up on this should that be requested by the reviewer.

[shemnon]

The gas cost appears to be specified in ethereum/EIPs#2129. While this is still open the got some positive feedback on the All Core Devs call. Can you finish the gas cost calculations and function registration based on these values?

[iikirilov]

@shemnon you will find that the gas requirement method already reflects this. Should this be abstracted to the FrontierGasCalculator?

[shemnon]

No need to bring it into frontier. You listed some other TODOs -

1. The precompile was not integrated with the precompile registry.
2. The EIP has not been finalized so some implementation details/test vectors may change.
3. The gas calculation was not tested.
4. The name of the precompile was not agreed.

For 1 this task is outstanding.
For 2 I am of the opinion the changes won't be dramatic, and likely there will be no more changes.
For 3 can you add some simple gas calculation tests based on the existing test vectors
For 4 lets call it "BLAKE2BF", if a different name comes up it's a trivial change we can handle later.

[iikirilov]

I have addressed the above. Waiting for the tests cases to be updated and we should be good to go.