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Explain code to overwrite fromAmount in comment

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Fixes MixBytes Comment 1.
This commit is contained in:
Jason Raymond Bell 2021-05-20 14:00:34 +01:00
parent b13a01d8b8
commit 11d0367d3c
1 changed files with 5 additions and 0 deletions
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5
contracts/adapters/BaseParaSwapSellAdapter.sol
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@ -66,9 +66,14 @@ abstract contract BaseParaSwapSellAdapter is BaseParaSwapAdapter {
IERC20(assetToSwapFrom).safeApprove(tokenTransferProxy, amountToSwap); IERC20(assetToSwapFrom).safeApprove(tokenTransferProxy, amountToSwap);
if (fromAmountOffset != 0) { if (fromAmountOffset != 0) {
// Ensure 256 bit (32 bytes) fromAmount value is within bounds of the
// calldata, not overlapping with the first 4 bytes (function selector).
require(fromAmountOffset >= 4 && require(fromAmountOffset >= 4 &&
fromAmountOffset <= swapCalldata.length.sub(32), fromAmountOffset <= swapCalldata.length.sub(32),
'FROM_AMOUNT_OFFSET_OUT_OF_RANGE'); 'FROM_AMOUNT_OFFSET_OUT_OF_RANGE');
// Overwrite the fromAmount with the correct amount for the swap.
// In memory, swapCalldata consists of a 256 bit length field, followed by
// the actual bytes data, that is why 32 is added to the byte offset.
assembly { assembly {
mstore(add(swapCalldata, add(fromAmountOffset, 32)), amountToSwap) mstore(add(swapCalldata, add(fromAmountOffset, 32)), amountToSwap)
} }