7 posts tagged with "solidity"

My last blog post about Bit Magic generated some buzz amongst fellow EVM developers and some of them reached out to me to include additional things in my blog related to using bits effectively in Solidity and the EVM in general.

Convert address to uint and back​

This conversion exploits the fact that addresses take up 20 bytes and so does a uint160 (20 * 8).

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.7;

// The theory behind this is that addresses take up 20 bytes in a word which is equivalent to (20*8) 160 bits and hence should be correctly casted to and from uint160.

contract AddressToUint {

    address public targetAddress;
    uint256 public targetUint;

    function convertAddressToUint(address _targetAddress) external returns(uint256) {
        targetAddress = _targetAddress;
        targetUint = uint256(uint160(_targetAddress));
        return targetUint;
    }

    function convertUintToAddress(uint256 _targetUint) external returns(address) {
        targetUint = _targetUint;
        targetAddress = address(uint160(_targetUint));
        return targetAddress;
    }

}

// 0xabD0127D996A468A79a0a8e88F4D419E40402e95
// 980877587572537262620952019491558306941665029781

Function Types​

For official documentations follow this link.

So, in Solidity, you can pass functions themselves as parameters to other functions. These type of parameters are called function types.

These function types can be used to pass and return functions from function calls.

Example​

1. Format of function types is the following:​

function (<parameter types>) {internal | external} [pure | view | payable] [returns(<return types>)]

Note : Function types can only be internal or external. Also, the return types cannot be empty if the function in question does not return anything, in this case, completely omit the returns keyword.

Bitwise Operations​

Includes all basic bitwise operations such as and, or, xor, not, shiftLeft, shiftRight etc.

uint x;
uint y;

x & y // and
x | y // or
x ^ y // xor
~x    // not
x << y // shift x by y bits to the left
x >> y // shift x by y bits to the right

Code snippets depicting modern Solidity​

//SPDX-License-Identifier: MIT

pragma solidity 0.8.14;

contract ModernSolidityFeatures {
    TestContract tcInstance = new TestContract();

    function modernFunctionSelector() public view returns(bytes4) {
        return tcInstance.square.selector;
    }
    
    function modernIsContract(address addr) public view returns(bool) {
        return (addr.code.length > 0 ? true : false);
    }

    function conventionalIsContract(address addr) public view returns(bool) {
        uint32 sizeOfAddressCodeSection;
        assembly {
            sizeOfAddressCodeSection := extcodesize(addr)
        }   
        return (sizeOfAddressCodeSection > 0);
    }

    function conventionalFunctionSelector(string memory functionSignature) public pure returns(bytes4) {
        return bytes4(keccak256(bytes(functionSignature)));
    }
}

contract TestContract {
    uint256 public number;

    function square(uint256 a) public pure returns(uint256) {
        return a*a;
    } 
}

Let us see today when and why do we use abi.encode vs abi.encodePacked.

What is a hash function?​

A hash function has the following characterisitics:

• A function that takes in arbitrary size input and outputs a data of fixed size
• Properties:
  • Deterministic
    • hash(x) = h, every time without fail
  • quick to compute the hash
  • irreversible
    • given h, (really)hard to find x such that hash(x) = h
  • small change in input changes the output significantly
    • hard to find x, y such that hash(x) = hash(y)

Jet:

Yul is part of a greater family of EVM assembly languages

its basically EVM assembly wrapped into a language with some Ssyntactic sugar

What's great about that is that the only thing you need to write Yul is an understanding of the EVM. Looking at Yul contracts won't really get you to that point

So, let's get a bit of a deeper understanding of the EVM

What is an EVM​

Consider Ethereum to be a global computer (with each node having its own permanent data store) and EVM is the processor. It basically handles smart contract deployment and execution. It is just a computation engine, and as such provides an abstraction of just computation and storage, similar to Java Virtual Machine(JVM).

The EVM executes its own bytecode intstruction set which higher level smart contract languages such as LLL, Serpent, Mutan or Solidity are compiled into. The EVM does not require to have any scheduling capability because Ethereum clients run through verified block transactions to determine which smart contract needs executing and in which order. This mechanism makes EVM a single-threaded mechanism.

1. A Turing machine is a finite (there are a limited number of states, such as a coin toss will have only two states: HEADS or TAILS) state machine that has an unlimited supply of paper tape that it can write on and read back.