Gas Effiecient Smart Contract

Do not create contracts
Use fixed sized-type variables
- use bytes32 instead of string or bytes
- use uint256 instead of uint32

Minimize the frequency of data storage

// Avoid
function ttt() {
    a = 1;
    b = 2;
    .... // do something
    c = 3;
    d = 4
}

// better
function ttt() {
    a = 1;
    b = 2;
    c = 3;
    d = 4;
    ... do something
}

// LOOP
uint cnt;

// avoid
function ttt() {
    for(...) {
        cnt++;
    }
}

// better
function ttt() {
    uint tmp = cnt;
    for(...) {
        tmp++;
    }
    cnt = tmp;
}

Data alignment (256 bits)

// Avoid
uint64 a;  --> x1
uint b     --> x2
byte c;    -|
uint64 d;  --> x3

// better
uint64 a;   -|
uint64 d;    |
byte c;     --> x1
uint b;     --> x2

Batch execution

gas cost
- standard tx: 21k
- external call: 1.4k

// avoid
function ttt(address user);

// better
function ttt(address[] users);
``

Short circuit rule

function a() --> cost 5k
function b() --> cost 20k

// should
if (a() || b()) {
    ...
}

Use external for functions only accessed externally. (not public)

Miscs

data storage (SSTORE)
- new: 20k (zero –> nonzero)
- modify: 5k
- delete: -15k (actual: -10k (-15k+5k) )
Instanbul hard fork
- SLOAD: 200 –> 800
- BALANCE: 400 –> 700
- input data:
  - nonzero: 68 –> 16
  - zero: still 4

Interesting fact

function b() public  --> cost n
function a() public  --> cost n+22

Function Name Optimization

Gas Effiecient Smart Contract

Miscs

tags note solidity

Read more

ZKP Study Group IV

Data availability proof in Eth2

如何升級智能合約

tags `note` `solidity`