Executing Swaps

Swap Functions

The exchange provides two primary swap functions:

Swap Exact Amount In

Specify the exact amount of tokens you want to sell, and receive at least a minimum amount:

function swapExactAmountIn(
    address tokenIn,
    address tokenOut,
    uint128 amountIn,
    uint128 minAmountOut
) external returns (uint128 amountOut)

• tokenIn - The token address you're selling
• tokenOut - The token address you're buying
• amountIn - The exact amount of tokenIn to sell
• minAmountOut - Minimum amount of tokenOut you'll accept (slippage protection)

• amountOut - The actual amount of tokenOut received

Example: Swap exactly 1000 USDC for at least 998 USDT:

uint128 amountOut = exchange.swapExactAmountIn(
    USDC_ADDRESS,
    USDT_ADDRESS,
    1000e6,      // Sell exactly 1000 USDC
    998e6        // Receive at least 998 USDT
);

Swap Exact Amount Out

Specify the exact amount of tokens you want to receive, and pay at most a maximum amount:

function swapExactAmountOut(
    address tokenIn,
    address tokenOut,
    uint128 amountOut,
    uint128 maxAmountIn
) external returns (uint128 amountIn)

• tokenIn - The token address you're selling
• tokenOut - The token address you're buying
• amountOut - The exact amount of tokenOut to receive
• maxAmountIn - Maximum amount of tokenIn you'll pay (slippage protection)

• amountIn - The actual amount of tokenIn spent

Example: Receive exactly 1000 USDT by spending at most 1002 USDC:

uint128 amountIn = exchange.swapExactAmountOut(
    USDC_ADDRESS,
    USDT_ADDRESS,
    1000e6,      // Receive exactly 1000 USDT
    1002e6       // Pay at most 1002 USDC
);

Quoting Prices

Before executing a swap, you can query the expected price using view functions that simulate the swap without executing it:

Quote Exact Amount In

function quoteSwapExactAmountIn(
    address tokenIn,
    address tokenOut,
    uint128 amountIn
) external view returns (uint128 amountOut)

Returns how much tokenOut you would receive for a given amountIn.

Quote Exact Amount Out

function quoteSwapExactAmountOut(
    address tokenIn,
    address tokenOut,
    uint128 amountOut
) external view returns (uint128 amountIn)

Returns how much tokenIn you would need to spend to receive a given amountOut.

// Check how much USDT you'd get for 1000 USDC
uint128 expectedOut = exchange.quoteSwapExactAmountIn(
    USDC_ADDRESS,
    USDT_ADDRESS,
    1000e6
);
 
// Only execute if the price is acceptable
if (expectedOut >= 998e6) {
    exchange.swapExactAmountIn(USDC_ADDRESS, USDT_ADDRESS, 1000e6, 998e6);
}

How Swaps Execute

When you call a swap function:

1. Balance Check: The contract first checks your balance on the DEX
2. Transfer if Needed: If your DEX balance is insufficient, tokens are transferred from your wallet
3. Order Matching: The DEX walks through orders at each price tick, from best to worst:
   • Orders are consumed in price-time priority order
   • Each filled order credits the maker's balance on the DEX
   • Continues until your swap is complete or limit price is reached
4. Slippage Check: Reverts if minAmountOut (or maxAmountIn) constraints aren't met
5. Settlement: Your output tokens are transferred to your wallet

Gas Costs

Swap gas costs scale with the number of orders and ticks your trade crosses:

• Base swap cost (transfers and setup)
• Per-order cost (for each order filled)
• Per-tick cost (for each price level crossed)
• Per-flip cost (if any flip orders are triggered)

Larger swaps that cross more orders will cost more gas, but the cost per unit of volume decreases.

Token Balances on the DEX

The DEX allows you to track token balances directly within the DEX contract, which saves gas by avoiding ERC-20 transfers on every trade. When you execute a swap, the contract first checks your DEX balance and only transfers from your wallet if needed.

For complete details on checking balances, depositing, withdrawing, and managing your DEX balance, see the DEX Balance page.