chore: Add code to implement pedersenHash/GetTreeKeyHash in javascript

[kevaundray]

This is a first pass at adding the code needed for pedersenHash/GetTreeKeyHash.

This would supercede #16

[kevaundray]

I'm not sure where this is called in the down stream package, though note that you likely don't want to implement calls like get_tree_key_for_version/balance/nonce as its done in the specs because those call get_tree_key independently whereas the only difference between their outputs is the last byte being swapped.

[holgerd77]

Thanks, two small first comments. 🙂

[gabrocheleau]

I will go ahead and merge this in.

In a subsequent PR I will clean the API up when possible, and add some documentation.

[holgerd77]

Hi Kev,
some additional comments here: we also need getTreeKeyHash() for optimization to not have this called over and over again with the same parameters from getTreeKey(), I will just expose this method in a quick follow-up release (so note is purely informational, nothing to do on your side).

Generally I am not so sure about the relation of Context.getTreeKey() and this standalone getTreeKey() coming from this file (and both exposed on the API level), can you clarify?

All the best
Holge

[holgerd77]

This Context thing needs to be "statefull" I assume?

Or could the methods on this also be static (at least partially)?

It would be a bit more convenient if it would not be necessary to initialize an initial context with new Context() and manage this object (what does this object do?) and just call Context.getTreeKey() (so, the captial Context, and not context).

In case all methods from Context could also be made static it would be even better if Context goes away completely and only the methods would be exposed directly.

If Context need to stay I would prefer another name, something more expressive and less generic (FFI ?).

[holgerd77]

I am confused, taking this from the EIP https://eips.ethereum.org/EIPS/eip-6800 ...

def get_tree_key(address: Address32, tree_index: int, sub_index: int):
    # Asssumes VERKLE_NODE_WIDTH = 256
    return (
        pedersen_hash(address + tree_index.to_bytes(32, 'little'))[:31] +
        bytes([sub_index])
    )
    
def get_tree_key_for_version(address: Address32):
    return get_tree_key(address, 0, VERSION_LEAF_KEY)

... tree_index is simply 0, while above it is such a complex byte value. 🤔 How is this coming together?