Constructing a Method ID on Solidity

Question

Good Afternoon Everybody! Based off the example on the official website. The example they provided was:

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.4.16 <0.9.0;

contract Foo {
    function bar(bytes3[2] memory) public pure {}
    function baz(uint32 x, bool y) public pure returns (bool r) { r = x > 32 || y; }
    function sam(bytes memory, bool, uint[] memory) public pure {}
}

In Following the example; I Understand to take the method name along with the parameters in its ASCII form and you should be able to produce 0xcdcd77c0(After taking its first 4 Bytes)

So in my quest to understand the process so that I may recreate it programmatically, I found an online Keccak-256 Converter and it produced:

cdcd77c0992ec5bbfc459984220f8c45084cc24d9b6efed1fae540db8de801d2

From My understanding the first 4 Bytes should be cdcd and that is not correct. So then I found myself down a rabbit hole and attempted to do a text > ASCII > Keccak Signature and that still did not produce what I needed.. So I am asking the community to help me understand how 4 bytes have turned into 10 characters.... Please and thank you.

Answer 1

Response from every hashing function, like keccak-256, are bytes or hex string representing those bytes. Every byte is represented by 2 characters in hex string. So 4 first bytes are 8 first characters. In you example there are

['cd', 'cd', '77', 'c0']

To indicate that some string should be interpreted as a bytes, there are prefixed with 0x.

When you combine those two rules you get 0xcdcd77c0 function selector.