FeeExperimental

SwapVM, the Aqua swap engine, evaluates fee instructions as part of a strategy program. This page documents an experimental fee family that applies fees to amountOut, together with volume-sensitive (progressive) fee formulas. These instructions extend the base Fee instruction set.

Experimental: not part of the shipped v1 fee set. The instructions on this page live in FeeExperimental.sol and are not registered on the deployed AquaSwapVMRouter. The shipped Aqua opcode set is Controls, XYCSwap, XYCConcentrate, Decay, Fee, PeggedSwap, and Extruction; the production Fee opcode applies fees to amountIn only.

The amountOut and progressive (volume-based) variants below are not available in Aqua v1, and there is no "LP Progressive Fees" product feature. In v1 only the LP swap fee is non-zero; protocol fees are 0 and are not shown. Treat this reference as a design record for review, not a description of on-chain behavior.

Source: src/instructions/FeeExperimental.sol

Fee scale: BPS = 1e9 (1e9 = 100%). feeBps is expressed on this scale, so feeBps = 1e9 is 100%.

Constraint shared by all instructions

Must be placed before swap amounts are computed (both amountIn and amountOut must be zero). Violating this reverts with FeeShouldBeAppliedBeforeSwapAmountsComputation.

Quote and swap divergence: in quote mode, token transfers and Aqua pulls are skipped. Quotes may succeed while swaps revert due to insufficient balance or missing approval. Do not use backward jumps to any of these instructions.

Instructions

_flatFeeAmountOutXD

Solidity
1
function _flatFeeAmountOutXD(Context memory ctx, bytes calldata args) internal

Flat proportional fee deducted from amountOut. No token transfer.

Field Offset Size Description
feeBps 0 4 bytes (uint32) Fee rate; max 1e9
Mode Behavior
exactIn Runs swap formula, then deducts amountOut × feeBps / BPS from result
exactOut Inflates amountOut by fee before passing to swap formula; restores taker-defined value after

_progressiveFeeInXD

Solidity
1
function _progressiveFeeInXD(Context memory ctx, bytes calldata args) internal

Volume-sensitive fee on amountIn. The effective fee increases as amountIn grows relative to balanceIn. Large swaps pay proportionally more.

Field Offset Size Description
feeBps 0 4 bytes (uint32) Base fee rate (λ); max 1e9

exactIn formula: amountIn_eff = (BPS × amountIn × balanceIn) / (BPS × balanceIn + feeBps × amountIn)

exactOut formula (inverse): amountIn = ⌈(BPS × amountIn_eff × balanceIn) / (BPS × balanceIn − feeBps × amountIn_eff)⌉

_progressiveFeeOutXD

Solidity
1
function _progressiveFeeOutXD(Context memory ctx, bytes calldata args) internal

Volume-sensitive fee on amountOut. The effective fee increases as amountOut grows relative to balanceOut.

Field Offset Size Description
feeBps 0 4 bytes (uint32) Base fee rate (λ); max 1e9

exactIn formula: amountOut_eff = (BPS × amountOut × balanceOut) / (BPS × balanceOut + feeBps × amountOut)

exactOut formula (inverse): amountOut = ⌈(BPS × amountOut_eff × balanceOut) / (BPS × balanceOut − feeBps × amountOut_eff)⌉

_protocolFeeAmountOutXD

Solidity
1
function _protocolFeeAmountOutXD(Context memory ctx, bytes calldata args) internal

Flat fee on amountOut with a live ERC-20 transfer from maker to a recipient.

Protocol fees are configured to 0 in Aqua v1, and this amountOut variant is not registered on the deployed router. It is documented here for design review only.

Field Offset Size Description
feeBps 0 4 bytes (uint32) Fee rate; max 1e9
to 4 20 bytes (address) Fee recipient

Runs the swap formula, deducts fee from amountOut, then calls safeTransferFrom(maker, to, feeAmount) on tokenOut.

_aquaProtocolFeeAmountOutXD

Solidity
1
function _aquaProtocolFeeAmountOutXD(Context memory ctx, bytes calldata args) internal

Same as _protocolFeeAmountOutXD but uses IAqua.pull(maker, orderHash, tokenOut, feeAmount, to) instead of a direct ERC-20 transfer.

Field Offset Size Description
feeBps 0 4 bytes (uint32) Fee rate; max 1e9
to 4 20 bytes (address) Fee recipient
  • Fee: the shipped fee instructions, applied to amountIn
  • XYCSwap: typical swap formula nested inside fee instructions
  • LimitSwap: another common nested swap formula

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