InterestRateModel

InterestRateModel is a pure library that turns pool utilization into a per-second borrow rate. It implements a kinked curve: a gentle slope up to the kink and a steep slope above it, so full utilization becomes expensive and liquidity returns to the pool. Stockline calls it during every accrual with the book’s IrmParams from RiskRegistry. The library has no external functions. InterestRateModel lets you:

Compute the per-second borrow rate for a given utilization and book
Round interest up so debt never accrues slower than the curve
Reject utilization above 100% or an invalid kink

InterestRateModel is a Solidity library. It is linked into the contracts that use it and has no address of its own. The source code is src/core/InterestRateModel.sol on GitHub. The ABI is /abis/InterestRateModel.json.

Pure functions

rate

function rate(
    uint256 utilization,
    IrmParams memory params
) internal pure returns (uint256)

Returns the per-second borrow rate for a utilization and a book’s curve. Below the kink the rate is baseRate + slopeBelowKink * u / kink. Above it the rate is baseRate + slopeBelowKink + slopeAboveKink * (u - kink) / (1 - kink). Reverts with UtilizationAboveWad above 1e18 and InvalidKink unless 0 < kink < 1e18.

Internal function. Divisions round up against the borrower. Parameters are already per-second; the library does not convert from APY.

Input parameters

Name	Type	Description
utilization	`uint256`	Borrowed divided by supplied, in WAD (1e18 = 100%).
params	`IrmParams`	IrmParams struct: `baseRate`, `slopeBelowKink`, `slopeAboveKink` (per-second WAD), `kink` (utilization WAD).

Return values

Type	Description
`uint256`	Per-second borrow rate in WAD. Multiply by 31,536,000 for a simple annual rate.

_mulDivUp

function _mulDivUp(
    uint256 a,
    uint256 b,
    uint256 d
) private pure returns (uint256)

ceil(a * b / d). Borrow interest rounds against the borrower.

Input parameters

Name	Type	Description
a	`uint256`
b	`uint256`
d	`uint256`

Return values

Type	Description
`uint256`

Errors

UtilizationAboveWad

error UtilizationAboveWad(uint256 utilization)

The utilization argument is above 1e18.

InvalidKink

error InvalidKink(uint64 kink)

The kink is 0 or 1e18 or more.

Introduction

Using Stockline

Concepts

Developers

Ecosystem

Resources

Pure functions

rate

_mulDivUp

Errors

UtilizationAboveWad

InvalidKink

​Pure functions

​rate

​_mulDivUp

​Errors

​UtilizationAboveWad

​InvalidKink

Pure functions

rate

_mulDivUp

Errors

UtilizationAboveWad

InvalidKink