Bank - DeFiner.org

TheBank contract, as its name implied, mainly deals with the methods and variables related to the saving pool. It uses three variables to track the total amount of tokens in the pool and their allocations. For each token,
totalLoans[token] tracks total amount of token lend.
totalReserve[token] tracks total amount of token reserved.
totalCompound[token] tracks total amount of token in compound
Therefore, the total amount of token in the pool is the summation of these three variables. The token utilization ratio U, token reservation ratio R and compound ratio C are defined accordingly. 
There are three categories of methods in the contract. 
The first category of methods deals with the total amount of tokens in the pool and their allocations. They are used to query the pool status of a token.
getTotalDeposit
getPoolAmount
getTokenState
getCapitalUtilizationRatio
getCapitalCompoundRatio
The second category of methods deals with the deposit rate and borrow rate of tokens in the pool. They are used to update and get the rate indexes information of each specific token.
newRateIndexCheckpoint
getDepositRatePerBlock
getBorrowRatePerBlock
depositRateIndexNow
borrowRateIndexNow
getDepositAccruedRate
getBorrowAccruedRate
The third category of methods deals with all the operations on the funds in the saving pool. These functions actually modify the recorded pool status.
Deposit
Withdraw
Borrow
Repay
Update
For more details about the modifiers of the functions, please check the modifiers page.
getTotalDepositStore
function head
function getTotalDepositStore(address _token) public view returns(uint)
parameters:
_token: The address of the token you want to query for.
return:
The number of total deposit tokens.
description
The method returns the sum of totalLoans[token],totalReserve[token] and totalCompound[token].
getPoolAmount
function head
function getPoolAmount(address _token) public view returns(uint)
parameters
_token: The address of the token you want to query for.
return:
The total number of tokens that are not borrowed out in DeFiner's pool.
description
The method returns the sum of totalCompound[token] and totalReserve[token] .
getTokenState
function head
function getTokenState(address _token) public view returns (uint256 deposits, uint256 loans, uint256 reserveBalance, uint256 remainingAssets)
parameters
_token: The address of the token you want to query for.
return:
deposits: The total number of deposited tokens.
loans: The total number of borrowed tokens.
reserveBalance: The total number of tokens that are still in the reserve pool.
remainingAssets: The same as getPoolAmount.
description
The method returns total deposit, total loans, total reservation, and total available tokens of a specific token.
getCapitalUtilizationRatio
function head:
function getCapitalUtilizationRatio(address _token) public view returns(uint)
parameters:
_token: The address of the token you want to query for.
return:
The U ratio with the precision to 18 decimals.
description
The method returns U of a token, which is the ratio of the total loan to the total deposit.
getCapitalCompoundRatio
function head
function getCapitalCompoundRatio(address _token) public view returns(uint)
parameters: 
_token; The address of the token you want to query for.
return:
The C ratio with the precision to 18 decimals.
description
The method returns C of a token, which is the ratio of the total amount in Compound to the total deposit. 
newRateIndexCheckpoint
function head
function newRateIndexCheckpoint(address _token) public onlyAuthorized
parameters:
_token: The address of the token you want to query for.
description
Add a new checkpoint both on the deposit rate index curve and the borrow rate index curve. Same as Compound, DeFiner uses rate index curve to track the accumulated rate of a token. The rate index curve is updated whenever any operation on that token happens. The interests of a token earned in a specific period could be derived from the rate index curve quickly. 
getDepositRatePerBlock
function head
function getDepositRatePerBlock(address _token) public view returns(uint)
parameters
_token: The address of the token you want to query for.
return:
The current deposit rate per block of the token.
description
Get the per block deposit rate of a token, and it is calculated as follows
Deposit Rate=U×Borrow Rate+C×Compound Supply Rate\text{Deposit Rate} = U\times \text{Borrow Rate} + C\times \text{Compound Supply Rate}Deposit Rate=U×Borrow Rate+C×Compound Supply Rate
getBorrowRatePerBlock
function head
function getBorrowRatePerBlock(address _token) public view returns(uint)
parameters:
_token: The address of the token you want to query for.
return:
The current borrowing rate per block of the token.
description
Get the per block borrow rate of a token. If the token is supported in Compoud, the borrow rate is determined by the borrow rate and supply rate of Compound as
Borrow Rate=Compound Supply Rate×0.4+Compound Borrow Rate×0.6\text{Borrow Rate} = \text{Compound Supply Rate} \times 0.4 + \text{Compound Borrow Rate} \times 0.6Borrow Rate=Compound Supply Rate×0.4+Compound Borrow Rate×0.6
Otherwise,
Borrow Rate=0.03+U×0.15\text{Borrow Rate} = 0.03 + U\times 0.15 Borrow Rate=0.03+U×0.15
The numbers in the equations are the initial value of the variables and are configurable in GlobalConfig contract.
depositRateIndexNow
function head
function depositRateIndexNow(address _token) public view returns(uint)
parameters:
_token: The address of the token you want to query for.
return:
The current deposit rate index.
description
Get deposit rate index of the current block. If the current block is a checkpoint, this method returns the exact value on the deposit index curve. Otherwise, it returns an estimated value of the deposit rate index.
borrowRateIndexNow
function head
function borrowRateIndexNow(address _token) public view returns(uint)
parameters:
_token: The address of the token you want to query for.
return:
The current borrow rate index.
description
Get borrow rate index of the current block. If the current block is a checkpoint, this method returns the exact value on the borrow index curve. Otherwise, it returns an estimated value of the borrow rate index.
getDepositAccruedRate
function head
function getDepositAccruedRate(address _token, uint _depositRateRecordStart) external view returns (uint256)
parameters:
_token: The address of the token you want to query for.
_depositRateRecordStart: The start block you want to query accrued rate for.
  return:
Return the accrued deposit rate given a token and a start block with precision to 18 decimals.
description
The deposit accrued rate in a block gap from B1B_1B1​
 to B2B_2B2​
is Deposit Rate Index(B2)/Deposit Rate Index(B1)\text{Deposit Rate Index}(B_2)/\text{Deposit Rate Index}(B_1)Deposit Rate Index(B2​)/Deposit Rate Index(B1​)
 . HereB1B_1B1​
 is _depositRateRecordStart you specified in the parameter and B2B_2B2​
 should be the current block number. If you deposit n tokens at block B1B_1B1​
 , and the current block number is B2B_2B2​
, the tokens you have now should be Deposit Rate Index(B2)/Deposit Rate Index(B1)×n\text{Deposit Rate Index}(B_2)/\text{Deposit Rate Index}(B_1) \times nDeposit Rate Index(B2​)/Deposit Rate Index(B1​)×n
.
There should be a rate index created on _depositRateRecordStart block, otherwise, it will throw an error.
getBorrowAccruedRate
function head
function getBorrowAccruedRate(address _token, uint _borrowRateRecordStart) external view returns (uint256)
parameters: 
_token: The address of the token that you want to query for.
_borrowRateRecordStart: The start block you want to query accrued rate for.
return:
Return the accrued borrow rate given a token and a start block with precision to 18 decimals.
description
The borrow accrued rate in a block gap from B1B_1B1​
 to B2B_2B2​
 is Borrow Rate Index(B2)/Borrow Rate Index(B1)\text{Borrow Rate Index}(B_2)/\text{Borrow Rate Index}(B_1)Borrow Rate Index(B2​)/Borrow Rate Index(B1​)
 . It's similar to getDepositAccruedRate.
Deposit
function head
function deposit(address _to, address _token, uint256 _amount) external onlyAuthorized
parameters:
_to: The address of the account that tries to deposit.
_token: The address of the token you want to deposit.
_amount: The volume of tokens that you want to deposit.
description
This method will create a new checkpoint on the rate index curve. It will deposit the token to the individual account of msg.sender in Accounts contract. Then, it will update the pool balance, i.e. the value of totalReserve[token] and totalCompound[token] , accordingly.
The deposited token will be first added to the pool reservation. If the reservation ratio R exceeds 20%, the contract will deposit the token to Compound to reset R to be 15%.
Withdraw
function head
function withdraw(address _from, address _token, uint256 _amount) external onlyAuthorized returns(uint)
parameters
_from: The address of the account that tries to withdraw.
_token: The address of the kind of token you want to withdraw.
_amount: The volume of tokens you want to withdraw.
description
This method will create a new checkpoint on the rate index curve. The new deposit balance is tracked in the individual account of msg.sender in Accounts contract. The withdraw is allowed only if the account has enough balance and its loan value is still below the reduced borrow power after withdrawn. Then, the contract will update the pool balance by calling update method.
Borrow
function head
function borrow(address _from, address _token, uint256 _amount) external onlyAuthorized
parameters:
_from: The account that tries to borrow tokens.
_token: The address of the token that you want to borrow.
_amount: The volume of tokens that the user tries to borrow.
description
This method will create a new checkpoint on the rate index curve. The new borrowed balance is tracked in the individual account of msg.sender in Accounts contract. The borrow  is allowed only if the added loan value is below the borrow power. Then, the contract will update the pool balance by calling update method.
Repay
function head
function repay(address _to, address _token, uint256 _amount) external onlyAuthorized returns(uint)
parameters:
_to: The address that tries to repay.
_token: The address of the token that the account wants to repay.
_amount: The volume of tokens that the account wants to repay.
description
This method will create a new checkpoint on the rate index curve. The new borrowed balance is tracked in the individual account of msg.sender in Accounts contract. The borrow  is allowed only if the added loan value is below the borrow power. Then, the contract will update the pool balance by calling update method.
Update
function head
function update(address _token, uint _amount, ActionType _action) public onlyAuthorized returns(uint256 compoundAmount)
parameters: 
_token: The address of the token you want to update.
_amount: The volume of tokens involved in this operation.
_action: The type of action that changes the pool amount.
DepositAction
RepayAction
WithdrawAction
BorrowAction
descrption
This method is called whenever the token balance in the saving pool is changed. It checks if there is enough amount of a token in the pool, i.e. the market liquidity. If an account borrows or withdraws. When the balance of a token that changes in the pool, this method updates the allocation of the token in the reservation and the Compound.
If an account deposits or repay such that the reservation ratio exceeds 20%, the contract will deposit an extra amount of token to Compound and reset R to be 15%. On the other hand,  if an account withdraw or borrow such that the reservation ratio falls behind 10%, the contract will withdraw the token from Compound and try to reset R to be 15%. However, in this case, there might not be enough tokens in Compound so that the final R could be below 15%.
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