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[Testing] PR for testing gas report generation #3531

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[Testing] PR for testing gas report generation #3531

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6e0cd0d
Use unchecked to improve gas usage of ERC721
Amxx Jul 1, 2022
47e2eef
add unchecked comments
Amxx Jul 6, 2022
53cf64b
fix lint
Amxx Jul 6, 2022
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25 changes: 21 additions & 4 deletions contracts/token/ERC721/ERC721.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -282,7 +282,13 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {

_beforeTokenTransfer(address(0), to, tokenId);

_balances[to] += 1;
unchecked {
// Will not overflow unless all 2**256 token ids are minted to the same owner.
// Given that tokens are minted one by one, it is impossible in practice that
// this ever happens. Might change if allow batch minting.
// The ERC fails to describe this case.
_balances[to] += 1;
}
_owners[tokenId] = to;

emit Transfer(address(0), to, tokenId);
Expand All @@ -308,7 +314,11 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {
// Clear approvals
_approve(address(0), tokenId);

_balances[owner] -= 1;
unchecked {
// Cannot overflow, as that would require more tokens to be burned/transfered
// out then the owner initialy received through minting and transfering in.
_balances[owner] -= 1;
}
delete _owners[tokenId];

emit Transfer(owner, address(0), tokenId);
Expand Down Expand Up @@ -340,8 +350,15 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {
// Clear approvals from the previous owner
delete _tokenApprovals[tokenId];

_balances[from] -= 1;
_balances[to] += 1;
unchecked {
// `_balances[from]` cannot overflow for the same reason as described in `_burn`:
// `from`'s balance is the number of token held, which is at least one before the current
// transfer.
// `_balances[to]` could overflow in the conditions described in `_mint`. That would require
// all 2**256 token ids to be minted, which in practice is impossible.
_balances[from] -= 1;
_balances[to] += 1;
}
_owners[tokenId] = to;

emit Transfer(from, to, tokenId);
Expand Down