4

I was doing research on EVM and solidity and I came across this fact that the calldata/input data is created using RLP encoding and stuff. I know the process and I don't want to elaborate on that. My question is, what is the logic or maths behind choosing the first 4 bytes of data for identifying the method? Why not 5? Why not some other number? For example if the call data is: 0xee919d50000000000000000000000000000000000000000000000000000000000000001 Then why do we take only the first 4 bytes, i.e., ee919d50 as the method id and not more or fewer bytes?

I also read from the first answer to this question: How does the EVM find the entry of a called function? that said that if you want to implement your own logic, you can consider the first 8 bytes of data instead of first four bytes. I am interested in knowing the actual reason for selecting the number "4".

I would appreciate if someone could explain or point a resource that has a detailed explanation of this question.

3

As any engineering choice, it is a trade off.

This way you can address in theory 4.294.967.296 different methods in any single contract.

It is a reasonable choice because, even giving the (crazy big) possibility to have a collision in 99999 out 100000 cases, you are assured in any case of a lot of unique entries for methods in the single contract!

It seems enough for any possible contract, giving furthermore the presence of a code size limit of 24 kbytes or so (who ever saw a smart contract having 500 or 1000 methods? The major of them have five-to-twenty methods and that’s all).

On the other hand, using a maximum of 32 bit (I.e. 4 bytes) is a reasonable choice in order to efficiently address the hash table with the most of the cpu’s today presumably used to run EVM nodes.

Let’s say that 4 bytes (I.e. 32 bit) is the maximum possible number of entries easy to address using the majority of current CPUs.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.