PriceLib

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Title: PriceLib

Pure arithmetic for zero-coupon bond price computation and rate limit checking.

Functions

computePrice

Returns the zero-coupon bond price WAD^2 / (WAD + ratePerSecond * durationSeconds).

Returns WAD (par, 0% discount) when ratePerSecond == 0 or durationSeconds == 0.

The price lies in [0, WAD]: the buy branch (mulDivDown) can floor to 0 for very large ratePerSecond * durationSeconds, while the sell branch (mulDivUp) stays >= 1.

Rounds in the protected user's favor: down when the user buys (lower ceiling on what they pay), up when the user sells (higher floor on what they receive).

Input bound (ceil-branch mulDivUp headroom): with the seller-side rate capped by the uint40 limit rate, overflow would need durations exceeding ~1e65 seconds.

function computePrice(bool isBuy, uint256 ratePerSecond, uint256 durationSeconds) internal pure returns (uint256);

Parameters

Name	Type	Description
isBuy	bool	True when the protected user is the buyer (lend-side), false when the seller.
ratePerSecond	uint256	The interest rate per second, in WAD (1e18 = 100% per second).
durationSeconds	uint256	The duration in seconds.

Returns

Name	Type	Description
<none>	uint256	price The zero-coupon bond price, in WAD.

computeEffectiveRate

Returns the effective rate for the position side: max(policyRate, limitRate) for lenders (isBuy == true, floor protection) and min(policyRate, limitRate) for borrowers (isBuy == false, ceiling protection).

function computeEffectiveRate(bool isBuy, uint256 policyRate, uint256 limitRate) internal pure returns (uint256);

Parameters

Name	Type	Description
isBuy	bool	True for lend-side, false for borrow-side.
policyRate	uint256	The rate from the interest rate policy.
limitRate	uint256	The user's configured limit rate.

satisfiesRateLimit

Returns true if the executed price satisfies the user's rate limit constraint.

For lenders (isBuy == true): assets * WAD <= units * price (floor).

For borrowers (isBuy == false): assets * WAD >= units * price (ceiling).

Any fee must be folded into assets by the caller (e.g. via RouterLib.netBuyerPrice / netSellerPrice in BaseMigrationRatifier._ratifyRate).

Overflow safety: units and assets are uint128 from Midnight and price <= WAD (1e18), so both sides of the comparison fit in uint256.

function satisfiesRateLimit(
    bool isBuy,
    uint256 units,
    uint256 assets,
    uint256 limitRate,
    uint256 policyRate,
    uint256 duration
) internal pure returns (bool);

Parameters

Name	Type	Description
isBuy	bool	True for lend-side (floor protection), false for borrow-side (ceiling protection).
units	uint256	The number of market units in the take.
assets	uint256	The post-fee assets (sellerAssets for borrow, buyerAssets for lend).
limitRate	uint256	The user's configured limit rate per second.
policyRate	uint256	The rate from the interest rate policy.
duration	uint256	The duration in seconds used for price computation.