PolynomialFeeCalculator

{{
  "language": "Solidity",
  "sources": {
    "src/PolynomialFeeCalculator.sol": {
      "content": "// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import "./interface/IFeeCalculator.sol";

contract PolynomialFeeCalculator is IFeeCalculator {

    int256 public constant COEFFICIENT_SCALE = 1e18;

    struct PolynomialCoefficients {
        int256 a;  // R⁴
        int256 b;  // R³
        int256 c;  // R²
        int256 d;  // R¹
    }

    PolynomialCoefficients public coefficients;

    error InvalidRValue();

    constructor() {
        coefficients = PolynomialCoefficients({
            a: -625 * COEFFICIENT_SCALE / 100,    // -6.25
            b: -1523 * COEFFICIENT_SCALE / 100,   // -15.23
            c: -242 * COEFFICIENT_SCALE / 100,    // -2.42
            d: -18 * COEFFICIENT_SCALE / 100      // -0.18
        });
    }

    function calculateFee(int256 R) external view override returns (uint256 feeRateBps) {
        if (R > 0) revert InvalidRValue();
        // Price decline: Calculated using a polynomial curve
        // F(R) = aR⁴ + bR³ + cR² + dR
        int256 R2 = (R * R) / COEFFICIENT_SCALE;
        int256 R3 = (R2 * R) / COEFFICIENT_SCALE;
        int256 R4 = (R3 * R) / COEFFICIENT_SCALE;

        int256 F_raw = 0;
        F_raw += (coefficients.a * R4) / COEFFICIENT_SCALE;
        F_raw += (coefficients.b * R3) / COEFFICIENT_SCALE;
        F_raw += (coefficients.c * R2) / COEFFICIENT_SCALE;
        F_raw += (coefficients.d * R) / COEFFICIENT_SCALE;

        F_raw = (F_raw * 10000) / COEFFICIENT_SCALE;

        if (F_raw < 0) F_raw = -F_raw;
        feeRateBps = uint256(F_raw);
    }
}
"
    },
    "src/interface/IFeeCalculator.sol": {
      "content": "// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

interface IFeeCalculator {
    function calculateFee(int256 R) external view returns (uint256);
}
"
    }
  },
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