How to truncate the hash function output in Solidity?

Question

I'd like to keep an ID which is the first 32-bit of the hash function output in Solidity. I'm aware that "keccak256" output is of type:

bytes32

which is more larger than I want.

Question: How can I truncate the output of hash function (i.e. keccak256) from "bytes32" to "bytes2"?

Answer 1

You can directly convert to bytes2 from bytes32, as follows:

function test() constant returns(bytes2){
        return bytes2(keccak256("123"));
}

Hope it helps~