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Improve nearBalancedPool check #2898

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28 changes: 18 additions & 10 deletions contracts/contracts/strategies/algebra/StableSwapAMMStrategy.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -87,22 +87,30 @@ contract StableSwapAMMStrategy is InitializableAbstractStrategy {
}

/**
* @dev Checks the pool is balanced enough to allow deposits.
* @dev Checks the pool is balanced enough to allow deposits. The probe
* size is 0.1% of the smaller reserve, which keeps the probe small
* relative to liquidity so the quote reflects the pool's CURRENT
* marginal price rather than the slippage of the probe itself. This
* makes the check work the same for tiny bootstrap pools and large
* established pools alike.
*/
modifier nearBalancedPool() {
// OToken/asset price = asset / OToken
// Get the OToken/asset price for selling 1 OToken for asset
// As OToken is 1, the asset amount is the OToken/asset price
uint256 sellPrice = IPair(pool).getAmountOut(1e18, oToken);
(uint256 r0, uint256 r1, ) = IPair(pool).getReserves();
uint256 probe = (r0 < r1 ? r0 : r1) / 1000;
require(probe > 0, "Pool too small");

// Get the amount of OToken received from selling 1 asset. This is buying OToken.
uint256 oTokenAmount = IPair(pool).getAmountOut(1e18, asset);
// Amount of asset received for selling `probe` of OToken in.
uint256 sellOut = IPair(pool).getAmountOut(probe, oToken);
// Amount of OToken received for selling `probe` of asset in.
uint256 oTokenOut = IPair(pool).getAmountOut(probe, asset);

// If the pool is degenerate, then the pool is not valid and we can't deposit.
require(oTokenAmount > 0, "Pool degenerate");
require(oTokenOut > 0, "Pool degenerate");

// Convert to a OToken/asset price = asset / OToken
uint256 buyPrice = 1e36 / oTokenAmount;
// Normalize both quotes back to 1e18 pricing units so the comparison
// against pegPrice ± maxDepeg stays scale-invariant.
uint256 sellPrice = (sellOut * 1e18) / probe;
uint256 buyPrice = (probe * 1e18) / oTokenOut;

uint256 pegPrice = 1e18;

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