Function: swap(uint256 amount0Out, uint256 amount1Out, address to, byte[] data)

This function can be called to perform a swap. It also supports flash swaps.

Inputs

• amount0Out

  • Control: Arbitrary.

  • Constraints: amount0Out < _reserve0, amount0Out > 0 || amount1Out > 0.

  • Impact: Amount to get from the swap.

• amount1Out

  • Control: Arbitrary.

  • Constraints: amount1Out < _reserve1, amount0Out > 0 || amount1Out > 0.

  • Impact: Amount to get from the swap.

• to

  • Control: Arbitrary.

  • Constraints: to != _token0 && to != _token1.

  • Impact: Recipient of the output tokens and (optionally) implementer of the deltaSwapCall callback.

• data

  • Control: Arbitrary.

  • Constraints: None.

  • Impact: If not empty, a callback is made to the recipient with this data after the output assets are transferred — typically used to implement flash loans.

Branches and code coverage

Intended branches

• Optimistically sends the requested output to the recipient, invokes the recipient callback if required, computes input amounts, updates traded liquidity EMA, ensures K-invariant still holds (accounting for fees), and updates reserves.

  Test coverage

• Handles fee calculation if caller is GammaSwap pool.

  Test coverage

• Handles fee calculation if caller is not GammaSwap pool.

  Test coverage

Negative behavior

• Reverts if both amount0Out and amount1Out are zero.

  Negative test

• Reverts if amount0Out >= _reserve0.

  Negative test

• Reverts if amount1Out >= _reserve1.

  Negative test

• Reverts if to == _token0 || to == _token1.

  Negative test

• Reverts if the callback reverts.

  Negative test

• Reverts if amount0In == 0 && amount1In == 0.

  Negative test

• Reverts if K-invariant does not hold at the end of the transaction.

  Negative test

Function call analysis

• IDeltaSwapCallee(to).deltaSwapCall(msg.sender, amount0Out, amount1Out, data)

  • What is controllable? amount0Out, amount1Out, and data.

  • If the return value is controllable, how is it used and how can it go wrong? Not used.

  • What happens if it reverts, reenters or does other unusual control flow? Reverts are propagated upwards; reentrancy is prevented by reentrancy guards.

• IERC20(_token0).balanceOf(address(this))

  • What is controllable? Nothing.

  • If the return value is controllable, how is it used and how can it go wrong? Controllable by transferring assets to the contract — used to determine token0 input amount.

  • What happens if it reverts, reenters or does other unusual control flow? Reverts are propagated upwards; reentrancy is prevented by reentrancy guards.

• IERC20(_token1).balanceOf(address(this))

  • What is controllable? Nothing.

  • If the return value is controllable, how is it used and how can it go wrong? Controllable by transferring assets to the contract — used to determine token1 input amount.

  • What happens if it reverts, reenters or does other unusual control flow? Reverts are propagated upwards; reentrancy is prevented by reentrancy guards.

• DSMath.calcTradeLiquidity(amount0In, amount1In, _reserve0, _reserve1)

  • What is controllable? amount0In and amount1In.

  • If the return value is controllable, how is it used and how can it go wrong? It is influenced by amount0In and amount1In. Used as the trade volume.

  • What happens if it reverts, reenters or does other unusual control flow? Cannot revert nor reenter.

• this._updateLiquidityTradedEMA(...)

  • What is controllable? The first argument is the return value of the call above.

  • If the return value is controllable, how is it used and how can it go wrong? It is not directly controlled but influenced by the argument, which is used to update the EMA.

  • What happens if it reverts, reenters or does other unusual control flow? Cannot revert nor reenter.

• this.calcTradingFee(...)

  • What is controllable? The first argument is the return value of the call above.

  • If the return value is controllable, how is it used and how can it go wrong? Not directly controllable but influenced by the EMA.

  • What happens if it reverts, reenters or does other unusual control flow? Cannot revert nor reenter (only external call is made to the factory).

• IDeltaSwapFactory(this.factory).gsFee()

  • What is controllable? Nothing.

  • If the return value is controllable, how is it used and how can it go wrong? Not controllable.

  • What happens if it reverts, reenters or does other unusual control flow? Cannot revert; if it did, it would be propagated upward. Reentrancy is not possible due to reentrancy guards.