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JumpRateModel.sol
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JumpRateModel.sol
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// SPDX-License-Identifier: BSD-3-Clause
pragma solidity ^0.5.16;
import "./InterestRateModelInterface.sol";
import "../Utils/SafeMath.sol";
/**
* @title Compound's JumpRateModel Contract
* @author Compound
*/
contract JumpRateModel is InterestRateModelInterface {
using SafeMath for uint;
event NewInterestParams(uint baseRatePerBlock, uint multiplierPerBlock, uint jumpMultiplierPerBlock, uint kink);
/**
* @notice The approximate number of blocks per year that is assumed by the interest rate model
*/
uint public constant blocksPerYear = 2102400;
/**
* @notice The multiplier of utilization rate that gives the slope of the interest rate
*/
uint public multiplierPerBlock;
/**
* @notice The base interest rate which is the y-intercept when utilization rate is 0
*/
uint public baseRatePerBlock;
/**
* @notice The multiplierPerBlock after hitting a specified utilization point
*/
uint public jumpMultiplierPerBlock;
/**
* @notice The utilization point at which the jump multiplier is applied
*/
uint public kink;
/**
* @notice Construct an interest rate model
* @param baseRatePerYear The approximate target base APR, as a mantissa (scaled by 1e18)
* @param multiplierPerYear The rate of increase in interest rate wrt utilization (scaled by 1e18)
* @param jumpMultiplierPerYear The multiplierPerBlock after hitting a specified utilization point
* @param kink_ The utilization point at which the jump multiplier is applied
*/
constructor(uint baseRatePerYear, uint multiplierPerYear, uint jumpMultiplierPerYear, uint kink_) public {
baseRatePerBlock = baseRatePerYear.div(blocksPerYear);
multiplierPerBlock = multiplierPerYear.div(blocksPerYear);
jumpMultiplierPerBlock = jumpMultiplierPerYear.div(blocksPerYear);
kink = kink_;
emit NewInterestParams(baseRatePerBlock, multiplierPerBlock, jumpMultiplierPerBlock, kink);
}
/**
* @notice Calculates the utilization rate of the market: `borrows / (cash + borrows - reserves)`
* @param cash The amount of cash in the market
* @param borrows The amount of borrows in the market
* @param reserves The amount of reserves in the market (currently unused)
* @return The utilization rate as a mantissa between [0, 1e18]
*/
function utilizationRate(uint cash, uint borrows, uint reserves) public pure returns (uint) {
// Utilization rate is 0 when there are no borrows
if (borrows == 0) {
return 0;
}
return borrows.mul(1e18).div(cash.add(borrows).sub(reserves));
}
/**
* @notice Calculates the current borrow rate per block, with the error code expected by the market
* @param cash The amount of cash in the market
* @param borrows The amount of borrows in the market
* @param reserves The amount of reserves in the market
* @return The borrow rate percentage per block as a mantissa (scaled by 1e18)
*/
function getBorrowRate(uint cash, uint borrows, uint reserves) public view returns (uint) {
uint util = utilizationRate(cash, borrows, reserves);
if (util <= kink) {
return util.mul(multiplierPerBlock).div(1e18).add(baseRatePerBlock);
} else {
uint normalRate = kink.mul(multiplierPerBlock).div(1e18).add(baseRatePerBlock);
uint excessUtil = util.sub(kink);
return excessUtil.mul(jumpMultiplierPerBlock).div(1e18).add(normalRate);
}
}
/**
* @notice Calculates the current supply rate per block
* @param cash The amount of cash in the market
* @param borrows The amount of borrows in the market
* @param reserves The amount of reserves in the market
* @param reserveFactorMantissa The current reserve factor for the market
* @return The supply rate percentage per block as a mantissa (scaled by 1e18)
*/
function getSupplyRate(uint cash, uint borrows, uint reserves, uint reserveFactorMantissa) public view returns (uint) {
uint oneMinusReserveFactor = uint(1e18).sub(reserveFactorMantissa);
uint borrowRate = getBorrowRate(cash, borrows, reserves);
uint rateToPool = borrowRate.mul(oneMinusReserveFactor).div(1e18);
return utilizationRate(cash, borrows, reserves).mul(rateToPool).div(1e18);
}
}