Get address from public key in Solidity

Question

The address is the last 20 bytes of sha3(publicKey)

In Solidity, using assembly if needed, how could I splice the first 12 bytes from sha3(publicKey) and get the address? What I came up with runs out of gas:

bytes32 b = sha3(publicKey)
address signer;
assembly {
signer := mload(add(b, 0x0c) // skip the first 12 bytes, 0c in hex = 12
}

MLOAD(0XAB) loads the word (32 byte) located at the memory address 0XAB. Does my function fail because it is trying to load 20 byte only? Can MLOAD load only 20 byte?

Answer 1

This works:

return address(keccak256(publicKey) & (2**(8*21)-1));

2**(8*21)-1 is just a trick to get 0xFFFFFF... (40 Fs) without typing it. :-)

EDIT

As pointed out by @schnorr, there's no need for the mask:

return address(keccak256(publicKey));

Answer 2

From an answer to How to convert an bytes to address in Solidity? as well an answer to How to concatenate a bytes32[] array to a string?, I came up with this for converting a bytes32 keyHash to an address.

function getAddressFromPublicKey(bytes _publicKey) returns (address signer) {
    // Get address from public key
    bytes32 keyHash = keccak256(_publicKey);
    uint result = 0;
    for (uint i = keyHash.length-1; i+1 > 12; i--) {
      uint c = uint(keyHash[i]);
      uint to_inc = c * ( 16 ** ((keyHash.length - i-1) * 2));
      result += to_inc;
    }
    return address(result);
}

Answer 3

In solidity 0.5:

function calculateAddress(bytes memory pub) public pure returns (address addr) {
    bytes32 hash = keccak256(pub);
    assembly {
        mstore(0, hash)
        addr := mload(0)
    }    
}

Answer 4

This should work for Solidity 0.5.x:

bytes32 hash = keccak256(publicKey);
address wallet = address(uint160(bytes20(hash)));