Is it dangerous to name my function ccccvKygDv?

Question

For those keeping track at home, the function hash of a function named ccccvKygDv() is 0xffffffff, the same as a null address.

pragma solidity ^0.4.0;

contract NullFunction {
  function ccccvKygDv() public pure { }
}

contract NormalFunction {
  function NothingWrongHere() public pure { }
}

When I look at the opcodes of the two functions listed above, I get:

NothingWrongHere()

47 PUSH4 0xffffffff
52 AND
53 DUP1
54 PUSH4 0xb1f6260f

ccccvKygDv()

47 PUSH4 0xffffffff
52 AND
53 DUP1
54 PUSH4 0xffffffff

It looks like the data being pushed to the stack will overwrite some of the data needed for the function itself.

Is this a silly question? Absolutely, but I'm asking it so that I can understand how contracts work on the opcode level a bit better.

Answer 1

I believe this is just a bit mask.

The code loads the call data, shifts it to the right, and then does a bitwise AND with 0xFFFFFFFF to get the (now) bottom four bytes (the function selector).

Then it compares the four bytes extracted with the known function selector. It doesn't matter that the function signature you're looking for happens to be 0xFFFFFFFF.