mUSD
mUSD is a Meta Assets (mAssets) that is composed of USD stablecoin assets. The basket contains DAI, USDC and USDT.
An incentivised constant sum market maker with hard limits at max region. This supports low slippage swaps and applies penalties towards min and max regions. AMM produces a stablecoin (mAsset) and redirects lending market interest and swap fees to the savings contract, producing a second yield-bearing asset.
_minOutputQuantity is used to limit slippage when swapping, minting or redeeming. Useful for preventing Sandwich and Frontrunning attacks.
Contracts are upgradable except for integration contracts. The ProtocolDAO multisig can migrate the assets from one integration contract to another.
Note that the mUSD on Ethereum mainnet is not fungible with the mUSD on Polygon. This is due to the fact that the basket of underlying assets is separate and the composition is different.
On Ethereum mUSD is composed of DAI, USDC, USDT and sUSD. On Polygon mUSD is composed of DAI, USDC and USDT.
Contracts
Address
mUSD follows the ERC20 standard. The non-standard decreaseAllowance and increaseAllowance functions have been added to mitigate the well-known issues around setting allowances. These are based on the OpenZeppelin ERC20 implementation.
ERC-20 Functions
totalSupply()
function totalSupply () external returns (uint256)
Returns the amount of tokens in existence.
balanceOf()
function balanceOf () external returns (uint256)
Returns the amount of tokens owned by account.
transfer()
function transfer () external returns (bool)
Moves amount tokens from the caller's account to recipient.
Returns a boolean value indicating whether the operation succeeded.
Emits a {Transfer} event.
allowance()
function allowance () external returns (uint256)
Returns the remaining number of tokens thatspenderwill be allowed to spend on behalf ofownerthrough {transferFrom}. This is zero by default.
This value changes when {approve} or {transferFrom} are called.
approve()
function approve () external returns (bool)
Sets amount as the allowance of spender over the caller's tokens.
Returns a boolean value indicating whether the operation succeeded.
IMPORTANT: Beware that changing an allowance with this method brings the risk that someone may use both the old and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards: https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
Emits an {Approval} event.
transferFrom()
function transferFrom () external returns (bool)
Moves amount tokens from sender to recipient using the allowance mechanism. amount is then deducted from the caller's allowance.
Returns a boolean value indicating whether the operation succeeded.
Emits a {Transfer} event.
increaseAllowance()
function increaseAllowance () public returns (bool)
Atomically increases the allowance granted to spender by the caller.
This is an alternative to {approve} that can be used as a mitigation for problems described in {IERC20-approve}.
Emits an {Approval} event indicating the updated allowance.
Requirements:
spendercannot be the zero address.
decreaseAllowance()
function decreaseAllowance () public returns (bool)
Atomically decreases the allowance granted to spender by the caller.
This is an alternative to {approve} that can be used as a mitigation for problems described in {IERC20-approve}.
Emits an {Approval} event indicating the updated allowance.
Requirements:
spendercannot be the zero address.spendermust have allowance for the caller of at leastsubtractedValue.
Functions
mint()
function mint (address _input, uint256 _inputQuantity, uint256 _minOutputQuantity, address _recipient) external returns (uint256 mintOutput)
Mint a single bAsset, at a 1:1 ratio with the bAsset. This contract must have approval to spend the senders bAsset
Parameter
Type
Description
_input
address
Address of the bAsset to deposit for the minted mAsset.
_inputQuantity
uint256
Quantity in bAsset units
_minOutputQuantity
uint256
Minimum mAsset quantity to be minted. This protects against slippage.
_recipient
address
Recipient of the newly minted mAsset tokens
mintMulti()
function mintMulti (address[] _inputs, uint256[] _inputQuantities, uint256 _minOutputQuantity, address _recipient) external returns (uint256 mintOutput)
Mint with multiple bAssets, at a 1:1 ratio to mAsset. This contract must have approval to spend the senders bAssets
Parameter
Type
Description
_inputs
address[]
Non-duplicate address array of bASset addresses to deposit for the minted mAsset tokens.
_inputQuantities
uint256[]
Quantity of each bAsset to deposit for the minted mAsset. Order of array should mirror the above bAsset addresses.
_minOutputQuantity
uint256
Minimum mAsset quantity to be minted. This protects against slippage.
_recipient
address
Address to receive the newly minted mAsset tokens
getMintOutput()
function getMintOutput (address _input, uint256 _inputQuantity) external returns (uint256 mintOutput)
Get the projected output of a given mint
Parameter
Type
Description
_input
address
Address of the bAsset to deposit for the minted mAsset
_inputQuantity
uint256
Quantity in bAsset units
getMintMultiOutput()
function getMintMultiOutput (address[] _inputs, uint256[] _inputQuantities) external returns (uint256 mintOutput)
Get the projected output of a given mint
Parameter
Type
Description
_inputs
address[]
Non-duplicate address array of addresses to bAssets to deposit for the minted mAsset tokens.
_inputQuantities
uint256[]
Quantity of each bAsset to deposit for the minted mAsset.
swap()
function swap (address _input, address _output, uint256 _inputQuantity, uint256 _minOutputQuantity, address _recipient) external returns (uint256 swapOutput)
Swaps one bAsset for another bAsset using the bAsset addresses. bAsset <> bAsset swaps will incur a small fee (swapFee()).
Parameter
Type
Description
_input
address
Address of bAsset to deposit
_output
address
Address of bAsset to receive
_inputQuantity
uint256
Units of input bAsset to swap
_minOutputQuantity
uint256
Minimum quantity of the swap output asset. This protects against slippage
_recipient
address
Address to transfer output asset to
getSwapOutput()
function getSwapOutput (address _input, address _output, uint256 _inputQuantity) external returns (uint256 swapOutput)
Determines both if a trade is valid, and the expected fee or output. Swap is valid if it does not result in the input asset exceeding its maximum weight.
Parameter
Type
Description
_input
address
Address of bAsset to deposit
_output
address
Address of bAsset to receive
_inputQuantity
uint256
Units of input bAsset to swap
redeem()
function redeem (address _output, uint256 _mAssetQuantity, uint256 _minOutputQuantity, address _recipient) external returns (uint256 outputQuantity)
Redeems a specified quantity of mAsset in return for a bAsset specified by bAsset address. The bAsset is sent to the specified recipient. The bAsset quantity is relative to current vault balance levels and desired mAsset quantity. The quantity of mAsset is burnt as payment. A minimum quantity of bAsset is specified to protect against price slippage between the mAsset and bAsset.
Parameter
Type
Description
_output
address
Address of the bAsset to receive
_mAssetQuantity
uint256
Quantity of mAsset to redeem
_minOutputQuantity
uint256
Minimum bAsset quantity to receive for the burnt mAssets. This protects against slippage.
_recipient
address
Address to transfer the withdrawn bAssets to.
redeemMasset()
function redeemMasset (uint256 _mAssetQuantity, uint256[] _minOutputQuantities, address _recipient) external returns (uint256[] outputQuantities)
Credits a recipient with a proportionate amount of bAssets, relative to current vault balance levels and desired mAsset quantity. Burns the mAsset as payment.
Parameter
Type
Description
_mAssetQuantity
uint256
Quantity of mAsset to redeem
_minOutputQuantities
uint256[]
Min units of output to receive
_recipient
address
Address to credit the withdrawn bAssets
redeemExactBassets()
function redeemExactBassets (address[] _outputs, uint256[] _outputQuantities, uint256 _maxMassetQuantity, address _recipient) external returns (uint256 mAssetQuantity)
Credits a recipient with a certain quantity of selected bAssets, in exchange for burning the relative Masset quantity from the sender. Sender also incurs a small fee on the outgoing asset.
Parameter
Type
Description
_outputs
address[]
Addresses of the bAssets to receive
_outputQuantities
uint256[]
Units of the bAssets to redeem
_maxMassetQuantity
uint256
Maximum mAsset quantity to burn for the received bAssets. This protects against slippage.
_recipient
address
Address to receive the withdrawn bAssets
getRedeemOutput()
function getRedeemOutput (address _output, uint256 _mAssetQuantity) external returns (uint256 bAssetOutput)
Gets the estimated output from a given redeem
Parameter
Type
Description
_output
address
Address of the bAsset to receive
_mAssetQuantity
uint256
Quantity of mAsset to redeem
getRedeemExactBassetsOutput()
function getRedeemExactBassetsOutput (address[] _outputs, uint256[] _outputQuantities) external returns (uint256 mAssetQuantity)
Gets the estimated output from a given redeem
Parameter
Type
Description
_outputs
address[]
Addresses of the bAsset to receive
_outputQuantities
uint256[]
Quantities of bAsset to redeem
getBasket()
function getBasket () external returns (bool, bool)
Get basket details for Masset_MassetStructs.Basket
getBassets()
function getBassets () external returns (struct BassetPersonal[] personal, struct BassetData[] bData)
Get data for a all bAssets in basket
getBasset()
function getBasset (address _bAsset) external returns (struct BassetPersonal personal, struct BassetData bData)
Get data for a specific bAsset, if it exists
Parameter
Type
Description
_bAsset
address
Address of bAsset
getConfig()
function getConfig () external returns (struct InvariantConfig config)
Gets all config needed for general InvariantValidator calls
getPrice()
function getPrice () external returns (uint256 price, uint256 k)
Gets the price of the fpToken, and invariant value k
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