# Developer Docs

## Getting Started

These docs are a comprehensive guide to the Rifi protocol, based on the Rifi Whitepaper (May 2021).

### Networks

The Rifi Protocol is currently deployed on BSC Mainnet:

### Protocol Math

The Rifi protocol contracts use a system of exponential math, Exponential.sol, in order to represent fractional quantities with sufficient precision.

Most numbers are represented as a mantissa, an unsigned integer scaled by 1 * 10 ^ 18, in order to perform basic math at a high level of precision.

#### rToken and Underlying Decimals

Prices and exchange rates are scaled by the decimals unique to each asset; rTokens are BEP-20 tokens with 8 decimals, while their underlying tokens vary, and have a public member named decimals.

#### Interpreting Exchange Rates

The rToken Exchange Rate is scaled by the difference in decimals between the rToken and the underlying asset.

``oneRTokenInUnderlying =exchangeRateCurrent / (1 * 10 ^ (18 +underlyingDecimals -rTokenDecimals))``

Here is an example of finding the value of 1 rUSDT in USDT with Web3.js JavaScript.

``constrTokenDecimals = 8; // all rTokens have 8 decimal placesconst underlying = new web3.eth.Contract(erc20Abi, usdtAddress);const rToken = new web3.eth.Contract(rTokenAbi, rUsdtAddress);constunderlyingDecimals = awaitunderlying.methods.decimals().call();constexchangeRateCurrent = awaitrToken.methods.exchangeRateCurrent().call();const mantissa = 18 + parseInt(underlyingDecimals) - rTokenDecimals;constoneRTokenInUnderlying =exchangeRateCurrent / Math.pow(10, mantissa);console.log('1 rUSDT can be redeemed for', oneRTokenInUnderlying, 'USDT');``

To find the number of underlying tokens that can be redeemed for rTokens, multiply the number of rTokens by the above value oneRTokenInUnderlying.

``underlyingTokens = rTokenAmount *oneRTokenInUnderlying``

#### Calculating Accrued Interest

Interest rates for each market update on any block in which the ratio of borrowed assets to supplied assets in the market has changed. The amount interest rates are changed depends on the interest rate model smart contract implemented for the market, and the amount of change in the ratio of borrowed assets to supplied assets in the market.

Interest accrues to all suppliers and borrowers in a market when any address interacts with the market’s rToken contract, calling one of these functions: mint, redeem, borrow, or repay. Successful execution of one of these functions triggers theaccrueInterest method, which causes interest to be added to the underlying balance of every supplier and borrower in the market. Interest accrues for the current block, as well as each prior block in which the accrueInterest method was not triggered (no user interacted with the rToken contract). Interest rifis only during blocks in which the rToken contract has one of the aforementioned methods invoked.

Here is an example of supply interest accrual:

Alice supplies 1 USDT to the Rifi protocol. At the time of supply, the supplyRatePerBlock is 37893605 Wei, or 0.00000012 USDT per block. No one interacts with the rToken contract for 3 blocks. On the subsequent 4th block, Bob borrows some USDT. Alice’s underlying balance is now 1.00000050 USDT (which is 37893605 Wei times 4 blocks, plus the original 1 USDT). Alice’s underlying USDT balance in subsequent blocks will have interest accrued based on the new value of 1.00000050 USDT instead of the initial 1 USDT. Note that the supplyRatePerBlock value may change at any time.

#### Calculating the APY Using Rate Per Block

The Annual Percentage Yield (APY) for supplying or borrowing in each market can be calculated using the value of supplyRatePerBlock (for supply APY) or borrowRatePerBlock (for borrow APY) in this formula:

``Rate = rToken.supplyRatePerBlock(); // IntegerRate = 37893566USDT Mantissa = 1 * 10 ^ 18 (USDT has 18 decimal places)Blocks Per Day = 28800 (3 seconds per block)Days Per Year = 365APY = ((((Rate / USDT Mantissa * Blocks Per Day + 1) ^ Days Per Year)) - 1) * 100``

Here is an example of calculating the supply and borrow APY with Web3.js JavaScript:

``constusdtMantissa = 1e18;constblocksPerDay = 28800;  // 13.15 seconds per blockconstdaysPerYear = 365;const rToken = new web3.usdt.Contract(rUsdtAbi, rUsdtAddress);constsupplyRatePerBlock = awaitrToken.methods.supplyRatePerBlock().call();constborrowRatePerBlock = awaitrToken.methods.borrowRatePerBlock().call();const supplyApy = (((Math.pow((supplyRatePerBlock / usdtMantissa * blocksPerDay) + 1, daysPerYear))) - 1) * 100;const borrowApy = (((Math.pow((borrowRatePerBlock / usdtMantissa * blocksPerDay) + 1, daysPerYear))) - 1) * 100;console.log(Supply APY for USDT \${supplyApy} %);console.log(Borrow APY for USDT \${borrowApy} %);``

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