ERC721H

Most optimized batch minting ERC721 implementation in the EVM ecosystem. Rewrite of ERC721A in Huff.

Gas Comparison (ERC721H vs ERC721A vs OpenZeppelin's ERC721)

Tests	Huff	Azuki	Azuki (delta vs. Huff)	OZ	OZ (delta vs. Huff)
Mint 200	437,232	447,020	-9,788	4,999,553	-4,562,321
Mint 50	149,382	152,120	-2,738	1,273,403	-1,124,021
Safe Transfer To Receiver	63,550	65,436	-1,886	66,160	-2,610
Simple Burn 1 In	60,503	82,611	-22,108	38,893	+21,610
Simple Burn	38,342	60,214	-21,872	38,893	-551
Simple Safe Transfer To EOA	62,379	63,364	-985	64,151	-1,772
Simple Transfer 1 In	81,987	82,958	-971	61,271	+20,716
Simple Transfer 20 In	115,306	119,835	-4,529	61,271	+54,035
Simple Transfer	59,817	60,561	-744	61,271	-1,454

Gas Comparison - Methodology

General Approach:

1. Create minimal reference implementations using the ERC721A and OpenZeppelin libraries respectively, viewable under src/refs/
2. Created comparison test contract with identical tests for all 3 versions test/CompareERC721.t.sol
3. Wrote and ran script that extracts the gas use of the actual main call in each test and adds the 21k base transaction stipend to the total cost of all calls

Table Generation:

To generate the above table run the following commands

forge build # necessary to ensure no warnings in `forge test` output
forge test --match-contract CompareERC721Test --ffi -vvvv > gas-compare.txt
python script/extract_gas_cost_comparison.py

Using ERC721H

Using ERC721H - Security Considerations

• Excessively large, arbitrary ERC721H__START_TOKEN_ID values may lead to owner data storage slots colliding with other variables, leading to a suite of bugs / vulnerabilities

Naming Convention

• prefix all macros / constants / labels with {FileName}__ e.g. ERC721H__MY_MACRO
• exceptions to above rule
  • prefix storage slot constants with {FileName}_SLOT__
  • name the constructor and selector switch {FileName}_CONSTRUCTOR / {FileName}_SELECTOR_SWITCH respectively
  • function signature constants do not require a prefix
• prefix macros / labels / constants that are only meant for internal use (quasi private) with a double underscore e.g. __ERC721H__selectorSwitchEnd
• use camel case for labels / custom function signatures
• use snake case for macros / constants