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Use unchecked arithmetic in "_transfer", "_mint" and "_burn" (#3513)

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This commit is contained in:
Paul Razvan Berg
2022-07-01 23:40:30 +03:00
committed by GitHub
parent 7a8f269457
commit 5fbf494511
2 changed files with 10 additions and 3 deletions
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1
CHANGELOG.md
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@ -6,6 +6,7 @@
* `Address`: optimize `functionCall` by calling `functionCallWithValue` directly. ([#3468](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3468))
* `Address`: optimize `functionCall` functions by checking contract size only if there is no returned data. ([#3469](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3469))
* `GovernorCompatibilityBravo`: remove unused `using` statements ([#3506](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3506))
* `ERC20`: optimize `_transfer`, `_mint` and `_burn` by using `unchecked` arithmetic when possible. ([#3513](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3513))
## 4.7.0 (2022-06-29)

12
contracts/token/ERC20/ERC20.sol
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@ -237,8 +237,10 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
unchecked {
_balances[from] = fromBalance - amount;
// Overflow not possible: the sum of all balances is capped by totalSupply, and the sum is preserved by
// decrementing then incrementing.
_balances[to] += amount;
}
_balances[to] += amount;
emit Transfer(from, to, amount);
@ -260,7 +262,10 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
_beforeTokenTransfer(address(0), account, amount);
_totalSupply += amount;
_balances[account] += amount;
unchecked {
// Overflow not possible: balance + amount is at most totalSupply + amount, which is checked above.
_balances[account] += amount;
}
emit Transfer(address(0), account, amount);
_afterTokenTransfer(address(0), account, amount);
@ -286,8 +291,9 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
unchecked {
_balances[account] = accountBalance - amount;
// Overflow not possible: amount <= accountBalance <= totalSupply.
_totalSupply -= amount;
}
_totalSupply -= amount;
emit Transfer(account, address(0), amount);