`ECDSA.recover()` accepting signature from `calldata`?

[delaaxe]

🧐 Motivation

Current ECDSA.recover is accepting a signature typed bytes memory but since signatures are often passed as calldata, adding a method that reads the signature directly from calldata instead of copying to memory could be more gas efficient.

📝 Details

Alternative assembly code reading from calldata without copy:

bytes calldata signature

bytes32 r;
bytes32 s;
uint8 v;
assembly {
    r := calldataload(signature.offset)
    s := calldataload(add(signature.offset, 0x20))
    v := byte(0, calldataload(add(signature.offset, 0x40)))
}

Current code:

bytes memory signature

bytes32 r;
bytes32 s;
uint8 v;
assembly {
    r := mload(add(signature, 0x20))
    s := mload(add(signature, 0x40))
    v := byte(0, mload(add(signature, 0x60)))
}

[frangio]

I'm personally not excited about this. We keep adding variants and having a lot of duplicate code. I'd like to see Solidity allow us to write these functions in a generic way. See https://github.com/ethereum/solidity/issues/13207.

If someone is looking for a gas-efficient way to accept signatures they should not use this function (even with calldata array), instead they should use recover(bytes32 hash, bytes32 r, bytes32 vs).