CurveTricryptoOptimizedWETH.vy

# pragma version 0.3.10
# pragma optimize gas
# pragma evm-version paris
"""
@title CurveTricryptoOptimizedWETH
@author Curve.Fi
@license Copyright (c) Curve.Fi, 2020-2023 - all rights reserved
@notice A Curve AMM pool for 3 unpegged assets (e.g. ETH, BTC, USD).
@dev All prices in the AMM are with respect to the first token in the pool.
     Supports native token transfers.
"""

from vyper.interfaces import ERC20
implements: ERC20  # <--------------------- AMM contract is also the LP token.

# --------------------------------- Interfaces -------------------------------

interface Math:
    def geometric_mean(_x: uint256[N_COINS]) -> uint256: view
    def wad_exp(_power: int256) -> uint256: view
    def cbrt(x: uint256) -> uint256: view
    def reduction_coefficient(
        x: uint256[N_COINS], fee_gamma: uint256
    ) -> uint256: view
    def newton_D(
        ANN: uint256,
        gamma: uint256,
        x_unsorted: uint256[N_COINS],
        K0_prev: uint256
    ) -> uint256: view
    def get_y(
        ANN: uint256,
        gamma: uint256,
        x: uint256[N_COINS],
        D: uint256,
        i: uint256,
    ) -> uint256[2]: view
    def get_p(
        _xp: uint256[N_COINS], _D: uint256, _A_gamma: uint256[2],
    ) -> uint256[N_COINS-1]: view

interface WETH:
    def deposit(): payable
    def withdraw(_amount: uint256): nonpayable

interface Factory:
    def admin() -> address: view
    def fee_receiver() -> address: view
    def views_implementation() -> address: view

interface Views:
    def calc_token_amount(
        amounts: uint256[N_COINS], deposit: bool, swap: address
    ) -> uint256: view
    def get_dy(
        i: uint256, j: uint256, dx: uint256, swap: address
    ) -> uint256: view
    def get_dx(
        i: uint256, j: uint256, dy: uint256, swap: address
    ) -> uint256: view


# ------------------------------- Events -------------------------------------

event Transfer:
    sender: indexed(address)
    receiver: indexed(address)
    value: uint256

event Approval:
    owner: indexed(address)
    spender: indexed(address)
    value: uint256

event TokenExchange:
    buyer: indexed(address)
    sold_id: uint256
    tokens_sold: uint256
    bought_id: uint256
    tokens_bought: uint256
    fee: uint256
    packed_price_scale: uint256

event AddLiquidity:
    provider: indexed(address)
    token_amounts: uint256[N_COINS]
    fee: uint256
    token_supply: uint256
    packed_price_scale: uint256

event RemoveLiquidity:
    provider: indexed(address)
    token_amounts: uint256[N_COINS]
    token_supply: uint256

event RemoveLiquidityOne:
    provider: indexed(address)
    token_amount: uint256
    coin_index: uint256
    coin_amount: uint256
    approx_fee: uint256
    packed_price_scale: uint256

event CommitNewParameters:
    deadline: indexed(uint256)
    mid_fee: uint256
    out_fee: uint256
    fee_gamma: uint256
    allowed_extra_profit: uint256
    adjustment_step: uint256
    ma_time: uint256

event NewParameters:
    mid_fee: uint256
    out_fee: uint256
    fee_gamma: uint256
    allowed_extra_profit: uint256
    adjustment_step: uint256
    ma_time: uint256

event RampAgamma:
    initial_A: uint256
    future_A: uint256
    initial_gamma: uint256
    future_gamma: uint256
    initial_time: uint256
    future_time: uint256

event StopRampA:
    current_A: uint256
    current_gamma: uint256
    time: uint256

event ClaimAdminFee:
    admin: indexed(address)
    tokens: uint256


# ----------------------- Storage/State Variables ----------------------------

WETH20: public(immutable(address))

N_COINS: constant(uint256) = 3
PRECISION: constant(uint256) = 10**18  # <------- The precision to convert to.
A_MULTIPLIER: constant(uint256) = 10000
packed_precisions: uint256

MATH: public(immutable(Math))
coins: public(immutable(address[N_COINS]))
factory: public(address)

price_scale_packed: uint256  # <------------------------ Internal price scale.
price_oracle_packed: uint256  # <------- Price target given by moving average.

last_prices_packed: uint256
last_prices_timestamp: public(uint256)

initial_A_gamma: public(uint256)
initial_A_gamma_time: public(uint256)

future_A_gamma: public(uint256)
future_A_gamma_time: public(uint256)  # <------ Time when ramping is finished.
#         This value is 0 (default) when pool is first deployed, and only gets
#        populated by block.timestamp + future_time in `ramp_A_gamma` when the
#                      ramping process is initiated. After ramping is finished
#      (i.e. self.future_A_gamma_time < block.timestamp), the variable is left
#                                                            and not set to 0.

balances: public(uint256[N_COINS])
D: public(uint256)
xcp_profit: public(uint256)
xcp_profit_a: public(uint256)  # <--- Full profit at last claim of admin fees.

virtual_price: public(uint256)  # <------ Cached (fast to read) virtual price.
#                          The cached `virtual_price` is also used internally.

# -------------- Params that affect how price_scale get adjusted -------------

packed_rebalancing_params: public(uint256)  # <---------- Contains rebalancing
#               parameters allowed_extra_profit, adjustment_step, and ma_time.

future_packed_rebalancing_params: uint256

# ---------------- Fee params that determine dynamic fees --------------------

packed_fee_params: public(uint256)  # <---- Packs mid_fee, out_fee, fee_gamma.
future_packed_fee_params: uint256

ADMIN_FEE: public(constant(uint256)) = 5 * 10**9  # <----- 50% of earned fees.
MIN_FEE: constant(uint256) = 5 * 10**5  # <-------------------------- 0.5 BPS.
MAX_FEE: constant(uint256) = 10 * 10**9
NOISE_FEE: constant(uint256) = 10**5  # <---------------------------- 0.1 BPS.

# ----------------------- Admin params ---------------------------------------

admin_actions_deadline: public(uint256)

ADMIN_ACTIONS_DELAY: constant(uint256) = 3 * 86400
MIN_RAMP_TIME: constant(uint256) = 86400

MIN_A: constant(uint256) = N_COINS**N_COINS * A_MULTIPLIER / 100
MAX_A: constant(uint256) = 1000 * A_MULTIPLIER * N_COINS**N_COINS
MAX_A_CHANGE: constant(uint256) = 10
MIN_GAMMA: constant(uint256) = 10**10
MAX_GAMMA: constant(uint256) = 5 * 10**16

PRICE_SIZE: constant(uint128) = 256 / (N_COINS - 1)
PRICE_MASK: constant(uint256) = 2**PRICE_SIZE - 1

# ----------------------- ERC20 Specific vars --------------------------------

name: public(immutable(String[64]))
symbol: public(immutable(String[32]))
decimals: public(constant(uint8)) = 18
version: public(constant(String[8])) = "v2.0.0"

balanceOf: public(HashMap[address, uint256])
allowance: public(HashMap[address, HashMap[address, uint256]])
totalSupply: public(uint256)
nonces: public(HashMap[address, uint256])

EIP712_TYPEHASH: constant(bytes32) = keccak256(
    "EIP712Domain(string name,string version,uint256 chainId,address verifyingContract,bytes32 salt)"
)
EIP2612_TYPEHASH: constant(bytes32) = keccak256(
    "Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)"
)
VERSION_HASH: constant(bytes32) = keccak256(version)
NAME_HASH: immutable(bytes32)
CACHED_CHAIN_ID: immutable(uint256)
salt: public(immutable(bytes32))
CACHED_DOMAIN_SEPARATOR: immutable(bytes32)


# ----------------------- Contract -------------------------------------------

@external
def __init__(
    _name: String[64],
    _symbol: String[32],
    _coins: address[N_COINS],
    _math: address,
    _weth: address,
    _salt: bytes32,
    packed_precisions: uint256,
    packed_A_gamma: uint256,
    packed_fee_params: uint256,
    packed_rebalancing_params: uint256,
    packed_prices: uint256,
):

    WETH20 = _weth
    MATH = Math(_math)

    self.factory = msg.sender

    name = _name
    symbol = _symbol
    coins = _coins

    self.packed_precisions = packed_precisions  # <------- Precisions of coins
    #                            are calculated as 10**(18 - coin.decimals()).

    self.initial_A_gamma = packed_A_gamma  # <------------------- A and gamma.
    self.future_A_gamma = packed_A_gamma

    self.packed_rebalancing_params = packed_rebalancing_params  # <-- Contains
    #               rebalancing params: allowed_extra_profit, adjustment_step,
    #                                                         and ma_exp_time.

    self.packed_fee_params = packed_fee_params  # <-------------- Contains Fee
    #                                  params: mid_fee, out_fee and fee_gamma.

    self.price_scale_packed = packed_prices
    self.price_oracle_packed = packed_prices
    self.last_prices_packed = packed_prices
    self.last_prices_timestamp = block.timestamp
    self.xcp_profit_a = 10**18

    #         Cache DOMAIN_SEPARATOR. If chain.id is not CACHED_CHAIN_ID, then
    #     DOMAIN_SEPARATOR will be re-calculated each time `permit` is called.
    #                   Otherwise, it will always use CACHED_DOMAIN_SEPARATOR.
    #                       see: `_domain_separator()` for its implementation.
    NAME_HASH = keccak256(name)
    salt = _salt
    CACHED_CHAIN_ID = chain.id
    CACHED_DOMAIN_SEPARATOR = keccak256(
        _abi_encode(
            EIP712_TYPEHASH,
            NAME_HASH,
            VERSION_HASH,
            chain.id,
            self,
            salt,
        )
    )

    log Transfer(empty(address), self, 0)  # <------- Fire empty transfer from
    #                                       0x0 to self for indexers to catch.


# ------------------- Token transfers in and out of the AMM ------------------


@payable
@external
def __default__():
    if msg.value > 0:
        assert WETH20 in coins


@internal
def _transfer_in(
    _coin: address,
    dx: uint256,
    dy: uint256,
    mvalue: uint256,
    callbacker: address,
    callback_sig: bytes32,
    sender: address,
    receiver: address,
    use_eth: bool
):
    """
    @notice Transfers `_coin` from `sender` to `self` and calls `callback_sig`
            if it is not empty.
    @dev The callback sig must have the following args:
         sender: address
         receiver: address
         coin: address
         dx: uint256
         dy: uint256
    @params _coin address of the coin to transfer in.
    @params dx amount of `_coin` to transfer into the pool.
    @params dy amount of `_coin` to transfer out of the pool.
    @params mvalue msg.value if the transfer is ETH, 0 otherwise.
    @params callbacker address to call `callback_sig` on.
    @params callback_sig signature of the callback function.
    @params sender address to transfer `_coin` from.
    @params receiver address to transfer `_coin` to.
    @params use_eth True if the transfer is ETH, False otherwise.
    """

    if use_eth and _coin == WETH20:
        assert mvalue == dx  # dev: incorrect eth amount
    else:
        assert mvalue == 0  # dev: nonzero eth amount

        if callback_sig == empty(bytes32):

            assert ERC20(_coin).transferFrom(
                sender, self, dx, default_return_value=True
            )

        else:

            # --------- This part of the _transfer_in logic is only accessible
            #                                                    by _exchange.

            #                 First call callback logic and then check if pool
            #                  gets dx amounts of _coins[i], revert otherwise.
            b: uint256 = ERC20(_coin).balanceOf(self)
            raw_call(
                callbacker,
                concat(
                    slice(callback_sig, 0, 4),
                    _abi_encode(sender, receiver, _coin, dx, dy)
                )
            )
            assert ERC20(_coin).balanceOf(self) - b == dx  # dev: callback didn't give us coins
            #                                          ^------ note: dx cannot
            #                   be 0, so the contract MUST receive some _coin.

        if _coin == WETH20:
            WETH(WETH20).withdraw(dx)  # <--------- if WETH was transferred in
            #           previous step and `not use_eth`, withdraw WETH to ETH.


@internal
def _transfer_out(
    _coin: address, _amount: uint256, use_eth: bool, receiver: address
):
    """
    @notice Transfer a single token from the pool to receiver.
    @dev This function is called by `remove_liquidity` and
         `remove_liquidity_one` and `_exchange` methods.
    @params _coin Address of the token to transfer out
    @params _amount Amount of token to transfer out
    @params use_eth Whether to transfer ETH or not
    @params receiver Address to send the tokens to
    """

    if use_eth and _coin == WETH20:
        raw_call(receiver, b"", value=_amount)
    else:
        if _coin == WETH20:
            WETH(WETH20).deposit(value=_amount)

        assert ERC20(_coin).transfer(
            receiver, _amount, default_return_value=True
        )


# -------------------------- AMM Main Functions ------------------------------


@payable
@external
@nonreentrant("lock")
def exchange(
    i: uint256,
    j: uint256,
    dx: uint256,
    min_dy: uint256,
    use_eth: bool = False,
    receiver: address = msg.sender
) -> uint256:
    """
    @notice Exchange using wrapped native token by default
    @param i Index value for the input coin
    @param j Index value for the output coin
    @param dx Amount of input coin being swapped in
    @param min_dy Minimum amount of output coin to receive
    @param use_eth True if the input coin is native token, False otherwise
    @param receiver Address to send the output coin to. Default is msg.sender
    @return uint256 Amount of tokens at index j received by the `receiver
    """
    return self._exchange(
        msg.sender,
        msg.value,
        i,
        j,
        dx,
        min_dy,
        use_eth,
        receiver,
        empty(address),
        empty(bytes32)
    )


@payable
@external
@nonreentrant('lock')
def exchange_underlying(
    i: uint256,
    j: uint256,
    dx: uint256,
    min_dy: uint256,
    receiver: address = msg.sender
) -> uint256:
    """
    @notice Exchange using native token transfers.
    @param i Index value for the input coin
    @param j Index value for the output coin
    @param dx Amount of input coin being swapped in
    @param min_dy Minimum amount of output coin to receive
    @param receiver Address to send the output coin to. Default is msg.sender
    @return uint256 Amount of tokens at index j received by the `receiver
    """
    return self._exchange(
        msg.sender,
        msg.value,
        i,
        j,
        dx,
        min_dy,
        True,
        receiver,
        empty(address),
        empty(bytes32)
    )


@external
@nonreentrant('lock')
def exchange_extended(
    i: uint256,
    j: uint256,
    dx: uint256,
    min_dy: uint256,
    use_eth: bool,
    sender: address,
    receiver: address,
    cb: bytes32
) -> uint256:
    """
    @notice Exchange with callback method.
    @dev This method does not allow swapping in native token, but does allow
         swaps that transfer out native token from the pool.
    @dev Does not allow flashloans
    @dev One use-case is to reduce the number of redundant ERC20 token
         transfers in zaps.
    @param i Index value for the input coin
    @param j Index value for the output coin
    @param dx Amount of input coin being swapped in
    @param min_dy Minimum amount of output coin to receive
    @param use_eth True if output is native token, False otherwise
    @param sender Address to transfer input coin from
    @param receiver Address to send the output coin to
    @param cb Callback signature
    @return uint256 Amount of tokens at index j received by the `receiver`
    """

    assert cb != empty(bytes32)  # dev: No callback specified
    return self._exchange(
        sender, 0, i, j, dx, min_dy, use_eth, receiver, msg.sender, cb
    )  # callbacker should never be self ------------------^


@payable
@external
@nonreentrant("lock")
def add_liquidity(
    amounts: uint256[N_COINS],
    min_mint_amount: uint256,
    use_eth: bool = False,
    receiver: address = msg.sender
) -> uint256:
    """
    @notice Adds liquidity into the pool.
    @param amounts Amounts of each coin to add.
    @param min_mint_amount Minimum amount of LP to mint.
    @param use_eth True if native token is being added to the pool.
    @param receiver Address to send the LP tokens to. Default is msg.sender
    @return uint256 Amount of LP tokens received by the `receiver
    """

    A_gamma: uint256[2] = self._A_gamma()
    xp: uint256[N_COINS] = self.balances
    amountsp: uint256[N_COINS] = empty(uint256[N_COINS])
    xx: uint256[N_COINS] = empty(uint256[N_COINS])
    d_token: uint256 = 0
    d_token_fee: uint256 = 0
    old_D: uint256 = 0

    assert amounts[0] + amounts[1] + amounts[2] > 0  # dev: no coins to add

    # --------------------- Get prices, balances -----------------------------

    precisions: uint256[N_COINS] = self._unpack(self.packed_precisions)
    packed_price_scale: uint256 = self.price_scale_packed
    price_scale: uint256[N_COINS-1] = self._unpack_prices(packed_price_scale)

    # -------------------------------------- Update balances and calculate xp.
    xp_old: uint256[N_COINS] = xp
    for i in range(N_COINS):
        bal: uint256 = xp[i] + amounts[i]
        xp[i] = bal
        self.balances[i] = bal
    xx = xp

    xp[0] *= precisions[0]
    xp_old[0] *= precisions[0]
    for i in range(1, N_COINS):
        xp[i] = unsafe_div(xp[i] * price_scale[i-1] * precisions[i], PRECISION)
        xp_old[i] = unsafe_div(
            xp_old[i] * unsafe_mul(price_scale[i-1], precisions[i]),
            PRECISION
        )

    # ---------------- transferFrom token into the pool ----------------------

    for i in range(N_COINS):

        if amounts[i] > 0:

            if coins[i] == WETH20:

                self._transfer_in(
                    coins[i],
                    amounts[i],
                    0,  # <-----------------------------------
                    msg.value,  #                             | No callbacks
                    empty(address),  # <----------------------| for
                    empty(bytes32),  # <----------------------| add_liquidity.
                    msg.sender,  #                            |
                    empty(address),  # <-----------------------
                    use_eth
                )

            else:

                self._transfer_in(
                    coins[i],
                    amounts[i],
                    0,
                    0,  # <----------------- mvalue = 0 if coin is not WETH20.
                    empty(address),
                    empty(bytes32),
                    msg.sender,
                    empty(address),
                    False  # <-------- use_eth is False if coin is not WETH20.
                )

            amountsp[i] = xp[i] - xp_old[i]

    # -------------------- Calculate LP tokens to mint -----------------------

    if self.future_A_gamma_time > block.timestamp:  # <--- A_gamma is ramping.

        # ----- Recalculate the invariant if A or gamma are undergoing a ramp.
        old_D = MATH.newton_D(A_gamma[0], A_gamma[1], xp_old, 0)

    else:

        old_D = self.D

    D: uint256 = MATH.newton_D(A_gamma[0], A_gamma[1], xp, 0)

    token_supply: uint256 = self.totalSupply
    if old_D > 0:
        d_token = token_supply * D / old_D - token_supply
    else:
        d_token = self.get_xcp(D)  # <------------------------- Making initial
        #                                            virtual price equal to 1.

    assert d_token > 0  # dev: nothing minted

    if old_D > 0:

        d_token_fee = (
            self._calc_token_fee(amountsp, xp) * d_token / 10**10 + 1
        )

        d_token -= d_token_fee
        token_supply += d_token
        self.mint(receiver, d_token)

        packed_price_scale = self.tweak_price(A_gamma, xp, D, 0)

    else:

        self.D = D
        self.virtual_price = 10**18
        self.xcp_profit = 10**18
        self.xcp_profit_a = 10**18
        self.mint(receiver, d_token)

    assert d_token >= min_mint_amount, "Slippage"

    log AddLiquidity(
        receiver, amounts, d_token_fee, token_supply, packed_price_scale
    )

    self._claim_admin_fees()  # <--------------------------- Claim admin fees.

    return d_token


@external
@nonreentrant("lock")
def remove_liquidity(
    _amount: uint256,
    min_amounts: uint256[N_COINS],
    use_eth: bool = False,
    receiver: address = msg.sender,
    claim_admin_fees: bool = True,
) -> uint256[N_COINS]:
    """
    @notice This withdrawal method is very safe, does no complex math since
            tokens are withdrawn in balanced proportions. No fees are charged.
    @param _amount Amount of LP tokens to burn
    @param min_amounts Minimum amounts of tokens to withdraw
    @param use_eth Whether to withdraw ETH or not
    @param receiver Address to send the withdrawn tokens to
    @param claim_admin_fees If True, call self._claim_admin_fees(). Default is True.
    @return uint256[3] Amount of pool tokens received by the `receiver`
    """
    amount: uint256 = _amount
    balances: uint256[N_COINS] = self.balances
    d_balances: uint256[N_COINS] = empty(uint256[N_COINS])

    if claim_admin_fees:
        self._claim_admin_fees()  # <------ We claim fees so that the DAO gets
        #         paid before withdrawal. In emergency cases, set it to False.

    # -------------------------------------------------------- Burn LP tokens.

    total_supply: uint256 = self.totalSupply  # <------ Get totalSupply before
    self.burnFrom(msg.sender, _amount)  # ---- reducing it with self.burnFrom.

    # There are two cases for withdrawing tokens from the pool.
    #   Case 1. Withdrawal does not empty the pool.
    #           In this situation, D is adjusted proportional to the amount of
    #           LP tokens burnt. ERC20 tokens transferred is proportional
    #           to : (AMM balance * LP tokens in) / LP token total supply
    #   Case 2. Withdrawal empties the pool.
    #           In this situation, all tokens are withdrawn and the invariant
    #           is reset.

    if amount == total_supply:  # <----------------------------------- Case 2.

        for i in range(N_COINS):

            d_balances[i] = balances[i]
            self.balances[i] = 0  # <------------------------- Empty the pool.

    else:  # <-------------------------------------------------------- Case 1.

        amount -= 1  # <---- To prevent rounding errors, favor LPs a tiny bit.

        for i in range(N_COINS):
            d_balances[i] = balances[i] * amount / total_supply
            assert d_balances[i] >= min_amounts[i]
            self.balances[i] = balances[i] - d_balances[i]
            balances[i] = d_balances[i]  # <-- Now it's the amounts going out.

    D: uint256 = self.D
    self.D = D - unsafe_div(D * amount, total_supply)  # <----------- Reduce D
    #      proportional to the amount of tokens leaving. Since withdrawals are
    #       balanced, this is a simple subtraction. If amount == total_supply,
    #                                                             D will be 0.

    # ---------------------------------- Transfers ---------------------------

    for i in range(N_COINS):
        self._transfer_out(coins[i], d_balances[i], use_eth, receiver)

    log RemoveLiquidity(msg.sender, balances, total_supply - _amount)

    return d_balances


@external
@nonreentrant("lock")
def remove_liquidity_one_coin(
    token_amount: uint256,
    i: uint256,
    min_amount: uint256,
    use_eth: bool = False,
    receiver: address = msg.sender
) -> uint256:
    """
    @notice Withdraw liquidity in a single token.
            Involves fees (lower than swap fees).
    @dev This operation also involves an admin fee claim.
    @param token_amount Amount of LP tokens to burn
    @param i Index of the token to withdraw
    @param min_amount Minimum amount of token to withdraw.
    @param use_eth Whether to withdraw ETH or not
    @param receiver Address to send the withdrawn tokens to
    @return Amount of tokens at index i received by the `receiver`
    """

    A_gamma: uint256[2] = self._A_gamma()

    dy: uint256 = 0
    D: uint256 = 0
    p: uint256 = 0
    xp: uint256[N_COINS] = empty(uint256[N_COINS])
    approx_fee: uint256 = 0

    # ---------------------------- Claim admin fees before removing liquidity.
    self._claim_admin_fees()

    # ------------------------------------------------------------------------

    dy, D, xp, approx_fee = self._calc_withdraw_one_coin(
        A_gamma,
        token_amount,
        i,
        (self.future_A_gamma_time > block.timestamp),  # <------- During ramps
    )  #                                                  we need to update D.

    assert dy >= min_amount, "Slippage"

    # ------------------------- Transfers ------------------------------------

    self.balances[i] -= dy
    self.burnFrom(msg.sender, token_amount)
    self._transfer_out(coins[i], dy, use_eth, receiver)

    packed_price_scale: uint256 = self.tweak_price(A_gamma, xp, D, 0)
    #        Safe to use D from _calc_withdraw_one_coin here ---^

    log RemoveLiquidityOne(
        msg.sender, token_amount, i, dy, approx_fee, packed_price_scale
    )

    return dy


@external
@nonreentrant("lock")
def claim_admin_fees():
    """
    @notice Claim admin fees. Callable by anyone.
    """
    self._claim_admin_fees()


# -------------------------- Packing functions -------------------------------


@internal
@view
def _pack(x: uint256[3]) -> uint256:
    """
    @notice Packs 3 integers with values <= 10**18 into a uint256
    @param x The uint256[3] to pack
    @return uint256 Integer with packed values
    """
    return (x[0] << 128) | (x[1] << 64) | x[2]


@internal
@view
def _unpack(_packed: uint256) -> uint256[3]:
    """
    @notice Unpacks a uint256 into 3 integers (values must be <= 10**18)
    @param val The uint256 to unpack
    @return uint256[3] A list of length 3 with unpacked integers
    """
    return [
        (_packed >> 128) & 18446744073709551615,
        (_packed >> 64) & 18446744073709551615,
        _packed & 18446744073709551615,
    ]


@internal
@view
def _pack_prices(prices_to_pack: uint256[N_COINS-1]) -> uint256:
    """
    @notice Packs N_COINS-1 prices into a uint256.
    @param prices_to_pack The prices to pack
    @return uint256 An integer that packs prices
    """
    packed_prices: uint256 = 0
    p: uint256 = 0
    for k in range(N_COINS - 1):
        packed_prices = packed_prices << PRICE_SIZE
        p = prices_to_pack[N_COINS - 2 - k]
        assert p < PRICE_MASK
        packed_prices = p | packed_prices
    return packed_prices


@internal
@view
def _unpack_prices(_packed_prices: uint256) -> uint256[2]:
    """
    @notice Unpacks N_COINS-1 prices from a uint256.
    @param _packed_prices The packed prices
    @return uint256[2] Unpacked prices
    """
    unpacked_prices: uint256[N_COINS-1] = empty(uint256[N_COINS-1])
    packed_prices: uint256 = _packed_prices
    for k in range(N_COINS - 1):
        unpacked_prices[k] = packed_prices & PRICE_MASK
        packed_prices = packed_prices >> PRICE_SIZE

    return unpacked_prices


# ---------------------- AMM Internal Functions -------------------------------


@internal
def _exchange(
    sender: address,
    mvalue: uint256,
    i: uint256,
    j: uint256,
    dx: uint256,
    min_dy: uint256,
    use_eth: bool,
    receiver: address,
    callbacker: address,
    callback_sig: bytes32
) -> uint256:

    assert i != j  # dev: coin index out of range
    assert dx > 0  # dev: do not exchange 0 coins

    A_gamma: uint256[2] = self._A_gamma()
    xp: uint256[N_COINS] = self.balances
    precisions: uint256[N_COINS] = self._unpack(self.packed_precisions)
    dy: uint256 = 0

    y: uint256 = xp[j]  # <----------------- if j > N_COINS, this will revert.
    x0: uint256 = xp[i]  # <--------------- if i > N_COINS, this will  revert.
    xp[i] = x0 + dx
    self.balances[i] = xp[i]

    packed_price_scale: uint256 = self.price_scale_packed
    price_scale: uint256[N_COINS - 1] = self._unpack_prices(
        packed_price_scale
    )

    xp[0] *= precisions[0]
    for k in range(1, N_COINS):
        xp[k] = unsafe_div(
            xp[k] * price_scale[k - 1] * precisions[k],
            PRECISION
        )  # <-------- Safu to do unsafe_div here since PRECISION is not zero.

    prec_i: uint256 = precisions[i]

    # ----------- Update invariant if A, gamma are undergoing ramps ---------

    t: uint256 = self.future_A_gamma_time
    if t > block.timestamp:

        x0 *= prec_i

        if i > 0:
            x0 = unsafe_div(x0 * price_scale[i - 1], PRECISION)

        x1: uint256 = xp[i]  # <------------------ Back up old value in xp ...
        xp[i] = x0                                                         # |
        self.D = MATH.newton_D(A_gamma[0], A_gamma[1], xp, 0)              # |
        xp[i] = x1  # <-------------------------------------- ... and restore.

    # ----------------------- Calculate dy and fees --------------------------

    D: uint256 = self.D
    prec_j: uint256 = precisions[j]
    y_out: uint256[2] = MATH.get_y(A_gamma[0], A_gamma[1], xp, D, j)
    dy = xp[j] - y_out[0]
    xp[j] -= dy
    dy -= 1

    if j > 0:
        dy = dy * PRECISION / price_scale[j - 1]
    dy /= prec_j

    fee: uint256 = unsafe_div(self._fee(xp) * dy, 10**10)

    dy -= fee  # <--------------------- Subtract fee from the outgoing amount.
    assert dy >= min_dy, "Slippage"

    y -= dy
    self.balances[j] = y  # <----------- Update pool balance of outgoing coin.

    y *= prec_j
    if j > 0:
        y = unsafe_div(y * price_scale[j - 1], PRECISION)
    xp[j] = y  # <------------------------------------------------- Update xp.

    # ---------------------- Do Transfers in and out -------------------------

    ########################## TRANSFER IN <-------
    self._transfer_in(
        coins[i], dx, dy, mvalue,
        callbacker, callback_sig,  # <-------- Callback method is called here.
        sender, receiver, use_eth,
    )

    ########################## -------> TRANSFER OUT
    self._transfer_out(coins[j], dy, use_eth, receiver)

    # ------ Tweak price_scale with good initial guess for newton_D ----------

    packed_price_scale = self.tweak_price(A_gamma, xp, 0, y_out[1])

    log TokenExchange(sender, i, dx, j, dy, fee, packed_price_scale)

    return dy


@internal
def tweak_price(
    A_gamma: uint256[2],
    _xp: uint256[N_COINS],
    new_D: uint256,
    K0_prev: uint256 = 0,
) -> uint256:
    """
    @notice Tweaks price_oracle, last_price and conditionally adjusts
            price_scale. This is called whenever there is an unbalanced
            liquidity operation: _exchange, add_liquidity, or
            remove_liquidity_one_coin.
    @dev Contains main liquidity rebalancing logic, by tweaking `price_scale`.
    @param A_gamma Array of A and gamma parameters.
    @param _xp Array of current balances.
    @param new_D New D value.
    @param K0_prev Initial guess for `newton_D`.
    """

    # ---------------------------- Read storage ------------------------------

    rebalancing_params: uint256[3] = self._unpack(
        self.packed_rebalancing_params
    )  # <---------- Contains: allowed_extra_profit, adjustment_step, ma_time.
    price_oracle: uint256[N_COINS - 1] = self._unpack_prices(
        self.price_oracle_packed
    )
    last_prices: uint256[N_COINS - 1] = self._unpack_prices(
        self.last_prices_packed
    )
    packed_price_scale: uint256 = self.price_scale_packed
    price_scale: uint256[N_COINS - 1] = self._unpack_prices(
        packed_price_scale
    )

    total_supply: uint256 = self.totalSupply
    old_xcp_profit: uint256 = self.xcp_profit
    old_virtual_price: uint256 = self.virtual_price
    last_prices_timestamp: uint256 = self.last_prices_timestamp

    # ----------------------- Update MA if needed ----------------------------

    if last_prices_timestamp < block.timestamp:

        #   The moving average price oracle is calculated using the last_price
        #      of the trade at the previous block, and the price oracle logged
        #              before that trade. This can happen only once per block.

        # ------------------ Calculate moving average params -----------------

        alpha: uint256 = MATH.wad_exp(
            -convert(
                unsafe_div(
                    (block.timestamp - last_prices_timestamp) * 10**18,
                    rebalancing_params[2]  # <----------------------- ma_time.
                ),
                int256,
            )
        )

        for k in range(N_COINS - 1):

            # ----------------- We cap state price that goes into the EMA with
            #                                                 2 x price_scale.
            price_oracle[k] = unsafe_div(
                min(last_prices[k], 2 * price_scale[k]) * (10**18 - alpha) +
                price_oracle[k] * alpha,  # ^-------- Cap spot price into EMA.
                10**18
            )

        self.price_oracle_packed = self._pack_prices(price_oracle)
        self.last_prices_timestamp = block.timestamp  # <---- Store timestamp.

    #                  price_oracle is used further on to calculate its vector
    #            distance from price_scale. This distance is used to calculate
    #                  the amount of adjustment to be done to the price_scale.

    # ------------------ If new_D is set to 0, calculate it ------------------

    D_unadjusted: uint256 = new_D
    if new_D == 0:  #  <--------------------------- _exchange sets new_D to 0.
        D_unadjusted = MATH.newton_D(A_gamma[0], A_gamma[1], _xp, K0_prev)

    # ----------------------- Calculate last_prices --------------------------

    last_prices = MATH.get_p(_xp, D_unadjusted, A_gamma)
    for k in range(N_COINS - 1):
        last_prices[k] = unsafe_div(last_prices[k] * price_scale[k], 10**18)
    self.last_prices_packed = self._pack_prices(last_prices)

    # ---------- Update profit numbers without price adjustment first --------

    xp: uint256[N_COINS] = empty(uint256[N_COINS])
    xp[0] = unsafe_div(D_unadjusted, N_COINS)
    for k in range(N_COINS - 1):
        xp[k + 1] = D_unadjusted * 10**18 / (N_COINS * price_scale[k])

    # ------------------------- Update xcp_profit ----------------------------

    xcp_profit: uint256 = 10**18
    virtual_price: uint256 = 10**18

    if old_virtual_price > 0:

        xcp: uint256 = MATH.geometric_mean(xp)
        virtual_price = 10**18 * xcp / total_supply

        xcp_profit = unsafe_div(
            old_xcp_profit * virtual_price,
            old_virtual_price
        )  # <---------------- Safu to do unsafe_div as old_virtual_price > 0.

        #       If A and gamma are not undergoing ramps (t < block.timestamp),
        #         ensure new virtual_price is not less than old virtual_price,
        #                                        else the pool suffers a loss.
        if self.future_A_gamma_time < block.timestamp:
            assert virtual_price > old_virtual_price, "Loss"

    self.xcp_profit = xcp_profit

    # ------------ Rebalance liquidity if there's enough profits to adjust it:
    if virtual_price * 2 - 10**18 > xcp_profit + 2 * rebalancing_params[0]:
        #                          allowed_extra_profit --------^

        # ------------------- Get adjustment step ----------------------------

        #                Calculate the vector distance between price_scale and
        #                                                        price_oracle.
        norm: uint256 = 0
        ratio: uint256 = 0
        for k in range(N_COINS - 1):

            ratio = unsafe_div(price_oracle[k] * 10**18, price_scale[k])
            # unsafe_div because we did safediv before ----^

            if ratio > 10**18:
                ratio = unsafe_sub(ratio, 10**18)
            else:
                ratio = unsafe_sub(10**18, ratio)
            norm = unsafe_add(norm, ratio**2)

        norm = isqrt(norm)  # <-------------------- isqrt is not in base 1e18.
        adjustment_step: uint256 = max(
            rebalancing_params[1], unsafe_div(norm, 5)
        )  #           ^------------------------------------- adjustment_step.

        if norm > adjustment_step:  # <---------- We only adjust prices if the
            #          vector distance between price_oracle and price_scale is
            #             large enough. This check ensures that no rebalancing
            #           occurs if the distance is low i.e. the pool prices are
            #                                     pegged to the oracle prices.

            # ------------------------------------- Calculate new price scale.

            p_new: uint256[N_COINS - 1] = empty(uint256[N_COINS - 1])
            for k in range(N_COINS - 1):
                p_new[k] = unsafe_div(
                    price_scale[k] * unsafe_sub(norm, adjustment_step)
                    + adjustment_step * price_oracle[k],
                    norm
                )  # <- norm is non-zero and gt adjustment_step; unsafe = safe

            # ---------------- Update stale xp (using price_scale) with p_new.
            xp = _xp
            for k in range(N_COINS - 1):
                xp[k + 1] = unsafe_div(_xp[k + 1] * p_new[k], price_scale[k])
                # unsafe_div because we did safediv before ----^

            # ------------------------------------------ Update D with new xp.
            D: uint256 = MATH.newton_D(A_gamma[0], A_gamma[1], xp, 0)

            for k in range(N_COINS):
                frac: uint256 = xp[k] * 10**18 / D  # <----- Check validity of
                assert (frac > 10**16 - 1) and (frac < 10**20 + 1)  #   p_new.

            xp[0] = D / N_COINS
            for k in range(N_COINS - 1):
                xp[k + 1] = D * 10**18 / (N_COINS * p_new[k])  # <---- Convert
                #                                           xp to real prices.

            # ---------- Calculate new virtual_price using new xp and D. Reuse
            #              `old_virtual_price` (but it has new virtual_price).
            old_virtual_price = unsafe_div(
                10**18 * MATH.geometric_mean(xp), total_supply
            )  # <----- unsafe_div because we did safediv before (if vp>1e18)

            # ---------------------------- Proceed if we've got enough profit.
            if (
                old_virtual_price > 10**18 and
                2 * old_virtual_price - 10**18 > xcp_profit
            ):

                packed_price_scale = self._pack_prices(p_new)

                self.D = D
                self.virtual_price = old_virtual_price
                self.price_scale_packed = packed_price_scale

                return packed_price_scale

    # --------- price_scale was not adjusted. Update the profit counter and D.
    self.D = D_unadjusted
    self.virtual_price = virtual_price

    return packed_price_scale


@internal
def _claim_admin_fees():
    """
    @notice Claims admin fees and sends it to fee_receiver set in the factory.
    """
    A_gamma: uint256[2] = self._A_gamma()

    xcp_profit: uint256 = self.xcp_profit  # <---------- Current pool profits.
    xcp_profit_a: uint256 = self.xcp_profit_a  # <- Profits at previous claim.
    total_supply: uint256 = self.totalSupply

    # Do not claim admin fees if:
    # 1. insufficient profits accrued since last claim, and
    # 2. there are less than 10**18 (or 1 unit of) lp tokens, else it can lead
    #    to manipulated virtual prices.
    if xcp_profit <= xcp_profit_a or total_supply < 10**18:
        return

    #      Claim tokens belonging to the admin here. This is done by 'gulping'
    #       pool tokens that have accrued as fees, but not accounted in pool's
    #         `self.balances` yet: pool balances only account for incoming and
    #                  outgoing tokens excluding fees. Following 'gulps' fees:

    for i in range(N_COINS):
        if coins[i] == WETH20:
            self.balances[i] = self.balance
        else:
            self.balances[i] = ERC20(coins[i]).balanceOf(self)

    #            If the pool has made no profits, `xcp_profit == xcp_profit_a`
    #                         and the pool gulps nothing in the previous step.

    vprice: uint256 = self.virtual_price

    #  Admin fees are calculated as follows.
    #      1. Calculate accrued profit since last claim. `xcp_profit`
    #         is the current profits. `xcp_profit_a` is the profits
    #         at the previous claim.
    #      2. Take out admin's share, which is hardcoded at 5 * 10**9.
    #         (50% => half of 100% => 10**10 / 2 => 5 * 10**9).
    #      3. Since half of the profits go to rebalancing the pool, we
    #         are left with half; so divide by 2.

    fees: uint256 = unsafe_div(
        unsafe_sub(xcp_profit, xcp_profit_a) * ADMIN_FEE, 2 * 10**10
    )

    # ------------------------------ Claim admin fees by minting admin's share
    #                                                of the pool in LP tokens.
    receiver: address = Factory(self.factory).fee_receiver()
    if receiver != empty(address) and fees > 0:

        frac: uint256 = vprice * 10**18 / (vprice - fees) - 10**18
        claimed: uint256 = self.mint_relative(receiver, frac)

        xcp_profit -= fees * 2

        self.xcp_profit = xcp_profit

        log ClaimAdminFee(receiver, claimed)

    # ------------------------------------------- Recalculate D b/c we gulped.
    D: uint256 = MATH.newton_D(A_gamma[0], A_gamma[1], self.xp(), 0)
    self.D = D

    # ------------------- Recalculate virtual_price following admin fee claim.
    #     In this instance we do not check if current virtual price is greater
    #               than old virtual price, since the claim process can result
    #                                     in a small decrease in pool's value.

    self.virtual_price = 10**18 * self.get_xcp(D) / self.totalSupply
    self.xcp_profit_a = xcp_profit  # <------------ Cache last claimed profit.


@internal
@view
def xp() -> uint256[N_COINS]:

    result: uint256[N_COINS] = self.balances
    packed_prices: uint256 = self.price_scale_packed
    precisions: uint256[N_COINS] = self._unpack(self.packed_precisions)

    result[0] *= precisions[0]
    for i in range(1, N_COINS):
        p: uint256 = (packed_prices & PRICE_MASK) * precisions[i]
        result[i] = result[i] * p / PRECISION
        packed_prices = packed_prices >> PRICE_SIZE

    return result


@view
@internal
def _A_gamma() -> uint256[2]:
    t1: uint256 = self.future_A_gamma_time

    A_gamma_1: uint256 = self.future_A_gamma
    gamma1: uint256 = A_gamma_1 & 2**128 - 1
    A1: uint256 = A_gamma_1 >> 128

    if block.timestamp < t1:

        # --------------- Handle ramping up and down of A --------------------

        A_gamma_0: uint256 = self.initial_A_gamma
        t0: uint256 = self.initial_A_gamma_time

        t1 -= t0
        t0 = block.timestamp - t0
        t2: uint256 = t1 - t0

        A1 = ((A_gamma_0 >> 128) * t2 + A1 * t0) / t1
        gamma1 = ((A_gamma_0 & 2**128 - 1) * t2 + gamma1 * t0) / t1

    return [A1, gamma1]


@internal
@view
def _fee(xp: uint256[N_COINS]) -> uint256:
    fee_params: uint256[3] = self._unpack(self.packed_fee_params)
    f: uint256 = MATH.reduction_coefficient(xp, fee_params[2])
    return unsafe_div(
        fee_params[0] * f + fee_params[1] * (10**18 - f),
        10**18
    )


@internal
@view
def get_xcp(D: uint256) -> uint256:

    x: uint256[N_COINS] = empty(uint256[N_COINS])
    x[0] = D / N_COINS
    packed_prices: uint256 = self.price_scale_packed  # <-- No precisions here
    #                                 because we don't switch to "real" units.

    for i in range(1, N_COINS):
        x[i] = D * 10**18 / (N_COINS * (packed_prices & PRICE_MASK))
        packed_prices = packed_prices >> PRICE_SIZE

    return MATH.geometric_mean(x)


@view
@internal
def _calc_token_fee(amounts: uint256[N_COINS], xp: uint256[N_COINS]) -> uint256:
    # fee = sum(amounts_i - avg(amounts)) * fee' / sum(amounts)
    fee: uint256 = unsafe_div(
        unsafe_mul(self._fee(xp), N_COINS),
        unsafe_mul(4, unsafe_sub(N_COINS, 1))
    )

    S: uint256 = 0
    for _x in amounts:
        S += _x

    avg: uint256 = unsafe_div(S, N_COINS)
    Sdiff: uint256 = 0

    for _x in amounts:
        if _x > avg:
            Sdiff += unsafe_sub(_x, avg)
        else:
            Sdiff += unsafe_sub(avg, _x)

    return fee * Sdiff / S + NOISE_FEE


@internal
@view
def _calc_withdraw_one_coin(
    A_gamma: uint256[2],
    token_amount: uint256,
    i: uint256,
    update_D: bool,
) -> (uint256, uint256, uint256[N_COINS], uint256):

    token_supply: uint256 = self.totalSupply
    assert token_amount <= token_supply  # dev: token amount more than supply
    assert i < N_COINS  # dev: coin out of range

    xx: uint256[N_COINS] = self.balances
    precisions: uint256[N_COINS] = self._unpack(self.packed_precisions)
    xp: uint256[N_COINS] = precisions
    D0: uint256 = 0

    # -------------------------- Calculate D0 and xp -------------------------

    price_scale_i: uint256 = PRECISION * precisions[0]
    packed_prices: uint256 = self.price_scale_packed
    xp[0] *= xx[0]
    for k in range(1, N_COINS):
        p: uint256 = (packed_prices & PRICE_MASK)
        if i == k:
            price_scale_i = p * xp[i]
        xp[k] = unsafe_div(xp[k] * xx[k] * p, PRECISION)
        packed_prices = packed_prices >> PRICE_SIZE

    if update_D:  # <-------------- D is updated if pool is undergoing a ramp.
        D0 = MATH.newton_D(A_gamma[0], A_gamma[1], xp, 0)
    else:
        D0 = self.D

    D: uint256 = D0

    # -------------------------------- Fee Calc ------------------------------

    # Charge fees on D. Roughly calculate xp[i] after withdrawal and use that
    # to calculate fee. Precision is not paramount here: we just want a
    # behavior where the higher the imbalance caused the more fee the AMM
    # charges.

    # xp is adjusted assuming xp[0] ~= xp[1] ~= x[2], which is usually not the
    #  case. We charge self._fee(xp), where xp is an imprecise adjustment post
    #  withdrawal in one coin. If the withdraw is too large: charge max fee by
    #   default. This is because the fee calculation will otherwise underflow.

    xp_imprecise: uint256[N_COINS] = xp
    xp_correction: uint256 = xp[i] * N_COINS * token_amount / token_supply
    fee: uint256 = self._unpack(self.packed_fee_params)[1]  # <- self.out_fee.

    if xp_correction < xp_imprecise[i]:
        xp_imprecise[i] -= xp_correction
        fee = self._fee(xp_imprecise)

    dD: uint256 = unsafe_div(token_amount * D, token_supply)
    D_fee: uint256 = fee * dD / (2 * 10**10) + 1  # <------- Actual fee on D.

    # --------- Calculate `approx_fee` (assuming balanced state) in ith token.
    # -------------------------------- We only need this for fee in the event.
    approx_fee: uint256 = N_COINS * D_fee * xx[i] / D

    # ------------------------------------------------------------------------
    D -= (dD - D_fee)  # <----------------------------------- Charge fee on D.
    # --------------------------------- Calculate `y_out`` with `(D - D_fee)`.
    y: uint256 = MATH.get_y(A_gamma[0], A_gamma[1], xp, D, i)[0]
    dy: uint256 = (xp[i] - y) * PRECISION / price_scale_i
    xp[i] = y

    return dy, D, xp, approx_fee


# ------------------------ ERC20 functions -----------------------------------


@internal
def _approve(_owner: address, _spender: address, _value: uint256):
    self.allowance[_owner][_spender] = _value

    log Approval(_owner, _spender, _value)


@internal
def _transfer(_from: address, _to: address, _value: uint256):
    assert _to not in [self, empty(address)]

    self.balanceOf[_from] -= _value
    self.balanceOf[_to] += _value

    log Transfer(_from, _to, _value)


@view
@internal
def _domain_separator() -> bytes32:
    if chain.id != CACHED_CHAIN_ID:
        return keccak256(
            _abi_encode(
                EIP712_TYPEHASH,
                NAME_HASH,
                VERSION_HASH,
                chain.id,
                self,
                salt,
            )
        )
    return CACHED_DOMAIN_SEPARATOR


@external
def transferFrom(_from: address, _to: address, _value: uint256) -> bool:
    """
    @dev Transfer tokens from one address to another.
    @param _from address The address which you want to send tokens from
    @param _to address The address which you want to transfer to
    @param _value uint256 the amount of tokens to be transferred
    @return bool True on successul transfer. Reverts otherwise.
    """
    _allowance: uint256 = self.allowance[_from][msg.sender]
    if _allowance != max_value(uint256):
        self._approve(_from, msg.sender, _allowance - _value)

    self._transfer(_from, _to, _value)
    return True


@external
def transfer(_to: address, _value: uint256) -> bool:
    """
    @dev Transfer token for a specified address
    @param _to The address to transfer to.
    @param _value The amount to be transferred.
    @return bool True on successful transfer. Reverts otherwise.
    """
    self._transfer(msg.sender, _to, _value)
    return True


@external
def approve(_spender: address, _value: uint256) -> bool:
    """
    @notice Allow `_spender` to transfer up to `_value` amount
            of tokens from the caller's account.
    @dev Non-zero to non-zero approvals are allowed, but should
         be used cautiously. The methods increaseAllowance + decreaseAllowance
         are available to prevent any front-running that may occur.
    @param _spender The account permitted to spend up to `_value` amount of
                    caller's funds.
    @param _value The amount of tokens `_spender` is allowed to spend.
    @return bool Success
    """
    self._approve(msg.sender, _spender, _value)
    return True


@external
def increaseAllowance(_spender: address, _add_value: uint256) -> bool:
    """
    @notice Increase the allowance granted to `_spender`.
    @dev This function will never overflow, and instead will bound
         allowance to max_value(uint256). This has the potential to grant an
         infinite approval.
    @param _spender The account to increase the allowance of.
    @param _add_value The amount to increase the allowance by.
    @return bool Success
    """
    cached_allowance: uint256 = self.allowance[msg.sender][_spender]
    allowance: uint256 = unsafe_add(cached_allowance, _add_value)

    if allowance < cached_allowance:  # <-------------- Check for an overflow.
        allowance = max_value(uint256)

    if allowance != cached_allowance:
        self._approve(msg.sender, _spender, allowance)

    return True


@external
def decreaseAllowance(_spender: address, _sub_value: uint256) -> bool:
    """
    @notice Decrease the allowance granted to `_spender`.
    @dev This function will never underflow, and instead will bound
        allowance to 0.
    @param _spender The account to decrease the allowance of.
    @param _sub_value The amount to decrease the allowance by.
    @return bool Success.
    """
    cached_allowance: uint256 = self.allowance[msg.sender][_spender]
    allowance: uint256 = unsafe_sub(cached_allowance, _sub_value)

    if cached_allowance < allowance:  # <------------- Check for an underflow.
        allowance = 0

    if allowance != cached_allowance:
        self._approve(msg.sender, _spender, allowance)

    return True


@external
def permit(
    _owner: address,
    _spender: address,
    _value: uint256,
    _deadline: uint256,
    _v: uint8,
    _r: bytes32,
    _s: bytes32,
) -> bool:
    """
    @notice Permit `_spender` to spend up to `_value` amount of `_owner`'s
            tokens via a signature.
    @dev In the event of a chain fork, replay attacks are prevented as
         domain separator is recalculated. However, this is only if the
         resulting chains update their chainId.
    @param _owner The account which generated the signature and is granting an
                  allowance.
    @param _spender The account which will be granted an allowance.
    @param _value The approval amount.
    @param _deadline The deadline by which the signature must be submitted.
    @param _v The last byte of the ECDSA signature.
    @param _r The first 32 bytes of the ECDSA signature.
    @param _s The second 32 bytes of the ECDSA signature.
    @return bool Success.
    """
    assert _owner != empty(address)  # dev: invalid owner
    assert block.timestamp <= _deadline  # dev: permit expired

    nonce: uint256 = self.nonces[_owner]
    digest: bytes32 = keccak256(
        concat(
            b"\x19\x01",
            self._domain_separator(),
            keccak256(
                _abi_encode(
                    EIP2612_TYPEHASH, _owner, _spender, _value, nonce, _deadline
                )
            ),
        )
    )
    assert ecrecover(digest, _v, _r, _s) == _owner  # dev: invalid signature

    self.nonces[_owner] = unsafe_add(nonce, 1)  # <-- Unsafe add is safe here.
    self._approve(_owner, _spender, _value)
    return True


@internal
def mint(_to: address, _value: uint256) -> bool:
    """
    @dev Mint an amount of the token and assigns it to an account.
         This encapsulates the modification of balances such that the
         proper events are emitted.
    @param _to The account that will receive the created tokens.
    @param _value The amount that will be created.
    @return bool Success.
    """
    self.totalSupply += _value
    self.balanceOf[_to] += _value

    log Transfer(empty(address), _to, _value)
    return True


@internal
def mint_relative(_to: address, frac: uint256) -> uint256:
    """
    @dev Increases supply by factor of (1 + frac/1e18) and mints it for _to
    @param _to The account that will receive the created tokens.
    @param frac The fraction of the current supply to mint.
    @return uint256 Amount of tokens minted.
    """
    supply: uint256 = self.totalSupply
    d_supply: uint256 = supply * frac / 10**18
    if d_supply > 0:
        self.totalSupply = supply + d_supply
        self.balanceOf[_to] += d_supply
        log Transfer(empty(address), _to, d_supply)

    return d_supply


@internal
def burnFrom(_to: address, _value: uint256) -> bool:
    """
    @dev Burn an amount of the token from a given account.
    @param _to The account whose tokens will be burned.
    @param _value The amount that will be burned.
    @return bool Success.
    """
    self.totalSupply -= _value
    self.balanceOf[_to] -= _value

    log Transfer(_to, empty(address), _value)
    return True


# ------------------------- AMM View Functions -------------------------------


@external
@view
def fee_receiver() -> address:
    """
    @notice Returns the address of the admin fee receiver.
    @return address Fee receiver.
    """
    return Factory(self.factory).fee_receiver()


@external
@view
def calc_token_amount(amounts: uint256[N_COINS], deposit: bool) -> uint256:
    """
    @notice Calculate LP tokens minted or to be burned for depositing or
            removing `amounts` of coins
    @dev Includes fee.
    @param amounts Amounts of tokens being deposited or withdrawn
    @param deposit True if it is a deposit action, False if withdrawn.
    @return uint256 Amount of LP tokens deposited or withdrawn.
    """
    view_contract: address = Factory(self.factory).views_implementation()
    return Views(view_contract).calc_token_amount(amounts, deposit, self)


@external
@view
def get_dy(i: uint256, j: uint256, dx: uint256) -> uint256:
    """
    @notice Get amount of coin[j] tokens received for swapping in dx amount of coin[i]
    @dev Includes fee.
    @param i index of input token. Check pool.coins(i) to get coin address at ith index
    @param j index of output token
    @param dx amount of input coin[i] tokens
    @return uint256 Exact amount of output j tokens for dx amount of i input tokens.
    """
    view_contract: address = Factory(self.factory).views_implementation()
    return Views(view_contract).get_dy(i, j, dx, self)


@external
@view
def get_dx(i: uint256, j: uint256, dy: uint256) -> uint256:
    """
    @notice Get amount of coin[i] tokens to input for swapping out dy amount
            of coin[j]
    @dev This is an approximate method, and returns estimates close to the input
         amount. Expensive to call on-chain.
    @param i index of input token. Check pool.coins(i) to get coin address at
           ith index
    @param j index of output token
    @param dy amount of input coin[j] tokens received
    @return uint256 Approximate amount of input i tokens to get dy amount of j tokens.
    """
    view_contract: address = Factory(self.factory).views_implementation()
    return Views(view_contract).get_dx(i, j, dy, self)


@external
@view
@nonreentrant("lock")
def lp_price() -> uint256:
    """
    @notice Calculates the current price of the LP token w.r.t coin at the
            0th index
    @return uint256 LP price.
    """

    price_oracle: uint256[N_COINS-1] = self._unpack_prices(
        self.price_oracle_packed
    )
    return (
        3 * self.virtual_price * MATH.cbrt(price_oracle[0] * price_oracle[1])
    ) / 10**24


@external
@view
@nonreentrant("lock")
def get_virtual_price() -> uint256:
    """
    @notice Calculates the current virtual price of the pool LP token.
    @dev Not to be confused with `self.virtual_price` which is a cached
         virtual price.
    @return uint256 Virtual Price.
    """
    return 10**18 * self.get_xcp(self.D) / self.totalSupply


@external
@view
@nonreentrant("lock")
def price_oracle(k: uint256) -> uint256:
    """
    @notice Returns the oracle price of the coin at index `k` w.r.t the coin
            at index 0.
    @dev The oracle is an exponential moving average, with a periodicity
         determined by `self.ma_time`. The aggregated prices are cached state
         prices (dy/dx) calculated AFTER the latest trade.
    @param k The index of the coin.
    @return uint256 Price oracle value of kth coin.
    """
    price_oracle: uint256 = self._unpack_prices(self.price_oracle_packed)[k]
    price_scale: uint256 = self._unpack_prices(self.price_scale_packed)[k]
    last_prices_timestamp: uint256 = self.last_prices_timestamp

    if last_prices_timestamp < block.timestamp:  # <------------ Update moving
        #                                                   average if needed.

        last_prices: uint256 = self._unpack_prices(self.last_prices_packed)[k]
        ma_time: uint256 = self._unpack(self.packed_rebalancing_params)[2]
        alpha: uint256 = MATH.wad_exp(
            -convert(
                (block.timestamp - last_prices_timestamp) * 10**18 / ma_time,
                int256,
            )
        )

        # ---- We cap state price that goes into the EMA with 2 x price_scale.
        return (
            min(last_prices, 2 * price_scale) * (10**18 - alpha) +
            price_oracle * alpha
        ) / 10**18

    return price_oracle


@external
@view
def last_prices(k: uint256) -> uint256:
    """
    @notice Returns last price of the coin at index `k` w.r.t the coin
            at index 0.
    @dev last_prices returns the quote by the AMM for an infinitesimally small swap
         after the last trade. It is not equivalent to the last traded price, and
         is computed by taking the partial differential of `x` w.r.t `y`. The
         derivative is calculated in `get_p` and then multiplied with price_scale
         to give last_prices.
    @param k The index of the coin.
    @return uint256 Last logged price of coin.
    """
    return self._unpack_prices(self.last_prices_packed)[k]


@external
@view
def price_scale(k: uint256) -> uint256:
    """
    @notice Returns the price scale of the coin at index `k` w.r.t the coin
            at index 0.
    @dev Price scale determines the price band around which liquidity is
         concentrated.
    @param k The index of the coin.
    @return uint256 Price scale of coin.
    """
    return self._unpack_prices(self.price_scale_packed)[k]


@external
@view
def fee() -> uint256:
    """
    @notice Returns the fee charged by the pool at current state.
    @dev Not to be confused with the fee charged at liquidity action, since
         there the fee is calculated on `xp` AFTER liquidity is added or
         removed.
    @return uint256 fee bps.
    """
    return self._fee(self.xp())


@view
@external
def calc_withdraw_one_coin(token_amount: uint256, i: uint256) -> uint256:
    """
    @notice Calculates output tokens with fee
    @param token_amount LP Token amount to burn
    @param i token in which liquidity is withdrawn
    @return uint256 Amount of ith tokens received for burning token_amount LP tokens.
    """

    return self._calc_withdraw_one_coin(
        self._A_gamma(),
        token_amount,
        i,
        (self.future_A_gamma_time > block.timestamp)
    )[0]


@external
@view
def calc_token_fee(
    amounts: uint256[N_COINS], xp: uint256[N_COINS]
) -> uint256:
    """
    @notice Returns the fee charged on the given amounts for add_liquidity.
    @param amounts The amounts of coins being added to the pool.
    @param xp The current balances of the pool multiplied by coin precisions.
    @return uint256 Fee charged.
    """
    return self._calc_token_fee(amounts, xp)


@view
@external
def A() -> uint256:
    """
    @notice Returns the current pool amplification parameter.
    @return uint256 A param.
    """
    return self._A_gamma()[0]


@view
@external
def gamma() -> uint256:
    """
    @notice Returns the current pool gamma parameter.
    @return uint256 gamma param.
    """
    return self._A_gamma()[1]


@view
@external
def mid_fee() -> uint256:
    """
    @notice Returns the current mid fee
    @return uint256 mid_fee value.
    """
    return self._unpack(self.packed_fee_params)[0]


@view
@external
def out_fee() -> uint256:
    """
    @notice Returns the current out fee
    @return uint256 out_fee value.
    """
    return self._unpack(self.packed_fee_params)[1]


@view
@external
def fee_gamma() -> uint256:
    """
    @notice Returns the current fee gamma
    @return uint256 fee_gamma value.
    """
    return self._unpack(self.packed_fee_params)[2]


@view
@external
def allowed_extra_profit() -> uint256:
    """
    @notice Returns the current allowed extra profit
    @return uint256 allowed_extra_profit value.
    """
    return self._unpack(self.packed_rebalancing_params)[0]


@view
@external
def adjustment_step() -> uint256:
    """
    @notice Returns the current adjustment step
    @return uint256 adjustment_step value.
    """
    return self._unpack(self.packed_rebalancing_params)[1]


@view
@external
def ma_time() -> uint256:
    """
    @notice Returns the current moving average time in seconds
    @dev To get time in seconds, the parameter is multipled by ln(2)
         One can expect off-by-one errors here.
    @return uint256 ma_time value.
    """
    return self._unpack(self.packed_rebalancing_params)[2] * 694 / 1000


@view
@external
def precisions() -> uint256[N_COINS]:  # <-------------- For by view contract.
    """
    @notice Returns the precisions of each coin in the pool.
    @return uint256[3] precisions of coins.
    """
    return self._unpack(self.packed_precisions)


@external
@view
def fee_calc(xp: uint256[N_COINS]) -> uint256:  # <----- For by view contract.
    """
    @notice Returns the fee charged by the pool at current state.
    @param xp The current balances of the pool multiplied by coin precisions.
    @return uint256 Fee value.
    """
    return self._fee(xp)


@view
@external
def DOMAIN_SEPARATOR() -> bytes32:
    """
    @notice EIP712 domain separator.
    @return bytes32 Domain Separator set for the current chain.
    """
    return self._domain_separator()


# ------------------------- AMM Admin Functions ------------------------------


@external
def ramp_A_gamma(
    future_A: uint256, future_gamma: uint256, future_time: uint256
):
    """
    @notice Initialise Ramping A and gamma parameter values linearly.
    @dev Only accessible by factory admin, and only
    @param future_A The future A value.
    @param future_gamma The future gamma value.
    @param future_time The timestamp at which the ramping will end.
    """
    assert msg.sender == Factory(self.factory).admin()  # dev: only owner
    assert block.timestamp > self.initial_A_gamma_time + (MIN_RAMP_TIME - 1)  # dev: ramp undergoing
    assert future_time > block.timestamp + MIN_RAMP_TIME - 1  # dev: insufficient time

    A_gamma: uint256[2] = self._A_gamma()
    initial_A_gamma: uint256 = A_gamma[0] << 128
    initial_A_gamma = initial_A_gamma | A_gamma[1]

    assert future_A > MIN_A - 1
    assert future_A < MAX_A + 1
    assert future_gamma > MIN_GAMMA - 1
    assert future_gamma < MAX_GAMMA + 1

    ratio: uint256 = 10**18 * future_A / A_gamma[0]
    assert ratio < 10**18 * MAX_A_CHANGE + 1
    assert ratio > 10**18 / MAX_A_CHANGE - 1

    ratio = 10**18 * future_gamma / A_gamma[1]
    assert ratio < 10**18 * MAX_A_CHANGE + 1
    assert ratio > 10**18 / MAX_A_CHANGE - 1

    self.initial_A_gamma = initial_A_gamma
    self.initial_A_gamma_time = block.timestamp

    future_A_gamma: uint256 = future_A << 128
    future_A_gamma = future_A_gamma | future_gamma
    self.future_A_gamma_time = future_time
    self.future_A_gamma = future_A_gamma

    log RampAgamma(
        A_gamma[0],
        future_A,
        A_gamma[1],
        future_gamma,
        block.timestamp,
        future_time,
    )


@external
def stop_ramp_A_gamma():
    """
    @notice Stop Ramping A and gamma parameters immediately.
    @dev Only accessible by factory admin.
    """
    assert msg.sender == Factory(self.factory).admin()  # dev: only owner

    A_gamma: uint256[2] = self._A_gamma()
    current_A_gamma: uint256 = A_gamma[0] << 128
    current_A_gamma = current_A_gamma | A_gamma[1]
    self.initial_A_gamma = current_A_gamma
    self.future_A_gamma = current_A_gamma
    self.initial_A_gamma_time = block.timestamp
    self.future_A_gamma_time = block.timestamp

    # ------ Now (block.timestamp < t1) is always False, so we return saved A.

    log StopRampA(A_gamma[0], A_gamma[1], block.timestamp)


@external
def commit_new_parameters(
    _new_mid_fee: uint256,
    _new_out_fee: uint256,
    _new_fee_gamma: uint256,
    _new_allowed_extra_profit: uint256,
    _new_adjustment_step: uint256,
    _new_ma_time: uint256,
):
    """
    @notice Commit new parameters.
    @dev Only accessible by factory admin.
    @param _new_mid_fee The new mid fee.
    @param _new_out_fee The new out fee.
    @param _new_fee_gamma The new fee gamma.
    @param _new_allowed_extra_profit The new allowed extra profit.
    @param _new_adjustment_step The new adjustment step.
    @param _new_ma_time The new ma time. ma_time is time_in_seconds/ln(2).
    """
    assert msg.sender == Factory(self.factory).admin()  # dev: only owner
    assert self.admin_actions_deadline == 0  # dev: active action

    _deadline: uint256 = block.timestamp + ADMIN_ACTIONS_DELAY
    self.admin_actions_deadline = _deadline

    # ----------------------------- Set fee params ---------------------------

    new_mid_fee: uint256 = _new_mid_fee
    new_out_fee: uint256 = _new_out_fee
    new_fee_gamma: uint256 = _new_fee_gamma

    current_fee_params: uint256[3] = self._unpack(self.packed_fee_params)

    if new_out_fee < MAX_FEE + 1:
        assert new_out_fee > MIN_FEE - 1  # dev: fee is out of range
    else:
        new_out_fee = current_fee_params[1]

    if new_mid_fee > MAX_FEE:
        new_mid_fee = current_fee_params[0]
    assert new_mid_fee <= new_out_fee  # dev: mid-fee is too high

    if new_fee_gamma < 10**18:
        assert new_fee_gamma > 0  # dev: fee_gamma out of range [1 .. 10**18]
    else:
        new_fee_gamma = current_fee_params[2]

    self.future_packed_fee_params = self._pack(
        [new_mid_fee, new_out_fee, new_fee_gamma]
    )

    # ----------------- Set liquidity rebalancing parameters -----------------

    new_allowed_extra_profit: uint256 = _new_allowed_extra_profit
    new_adjustment_step: uint256 = _new_adjustment_step
    new_ma_time: uint256 = _new_ma_time

    current_rebalancing_params: uint256[3] = self._unpack(self.packed_rebalancing_params)

    if new_allowed_extra_profit > 10**18:
        new_allowed_extra_profit = current_rebalancing_params[0]

    if new_adjustment_step > 10**18:
        new_adjustment_step = current_rebalancing_params[1]

    if new_ma_time < 872542:  # <----- Calculated as: 7 * 24 * 60 * 60 / ln(2)
        assert new_ma_time > 86  # dev: MA time should be longer than 60/ln(2)
    else:
        new_ma_time = current_rebalancing_params[2]

    self.future_packed_rebalancing_params = self._pack(
        [new_allowed_extra_profit, new_adjustment_step, new_ma_time]
    )

    # ---------------------------------- LOG ---------------------------------

    log CommitNewParameters(
        _deadline,
        new_mid_fee,
        new_out_fee,
        new_fee_gamma,
        new_allowed_extra_profit,
        new_adjustment_step,
        new_ma_time,
    )


@external
@nonreentrant("lock")
def apply_new_parameters():
    """
    @notice Apply committed parameters.
    @dev Only callable after admin_actions_deadline.
    """
    assert block.timestamp >= self.admin_actions_deadline  # dev: insufficient time
    assert self.admin_actions_deadline != 0  # dev: no active action

    self.admin_actions_deadline = 0

    packed_fee_params: uint256 = self.future_packed_fee_params
    self.packed_fee_params = packed_fee_params

    packed_rebalancing_params: uint256 = self.future_packed_rebalancing_params
    self.packed_rebalancing_params = packed_rebalancing_params

    rebalancing_params: uint256[3] = self._unpack(packed_rebalancing_params)
    fee_params: uint256[3] = self._unpack(packed_fee_params)

    log NewParameters(
        fee_params[0],
        fee_params[1],
        fee_params[2],
        rebalancing_params[0],
        rebalancing_params[1],
        rebalancing_params[2],
    )


@external
def revert_new_parameters():
    """
    @notice Revert committed parameters
    @dev Only accessible by factory admin. Setting admin_actions_deadline to 0
         ensures a revert in apply_new_parameters.
    """
    assert msg.sender == Factory(self.factory).admin()  # dev: only owner
    self.admin_actions_deadline = 0