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Use unchecked arithmetic in "_transfer" and "_mint" #3513

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merged 8 commits into from
Jul 1, 2022
Merged

Use unchecked arithmetic in "_transfer" and "_mint" #3513

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5d9652e
Use unchecked arithmetic in "_transfer" and "_mint"
PaulRBerg Jun 28, 2022
4cc291e
docs: mention erc20 unchecked optimization in changelog
PaulRBerg Jul 1, 2022
a7f638c
Update CHANGELOG.md
Amxx Jul 1, 2022
d7b06ee
Update ERC20.sol
Amxx Jul 1, 2022
43e931f
Update CHANGELOG.md
Amxx Jul 1, 2022
36e625f
add comments explaining lack of overflow
frangio Jul 1, 2022
69efce9
fix changelog
frangio Jul 1, 2022
cb8aa1c
fix function names in changelog
frangio Jul 1, 2022
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -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)

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12 changes: 9 additions & 3 deletions contracts/token/ERC20/ERC20.sol
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Expand Up @@ -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);

Expand All @@ -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);
Expand All @@ -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);

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