Solidity – How to Convert a uint to Bytes

To be even more efficient:

function toBytes(address a) public pure returns (bytes memory b){
    assembly {
        let m := mload(0x40)
        a := and(a, 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF)
        mstore(add(m, 20), xor(0x140000000000000000000000000000000000000000, a))
        mstore(0x40, add(m, 52))
        b := m
   }
}

Takes just 695 gas vs 2500 for Gokulnath's answer and 5000 for Eth's

Edit for solidity ^0.5.0:

This is almost as efficient and much more readable:

function toBytes(address a) public pure returns (bytes memory) {
    return abi.encodePacked(a);
}

I feel like there might be a more efficient way to do this but here's my naive solution:

function bytesToAddress (bytes b) constant returns (address) {
    uint result = 0;
    for (uint i = 0; i < b.length; i++) {
        uint c = uint(b[i]);
        if (c >= 48 && c <= 57) {
            result = result * 16 + (c - 48);
        }
        if(c >= 65 && c<= 90) {
            result = result * 16 + (c - 55);
        }
        if(c >= 97 && c<= 122) {
            result = result * 16 + (c - 87);
        }
    }
    return address(result);
}