validateSupply

Overview

• cache

• updateState

• validateSupply

• updateInterestRates

• transfer & mint

• If isFirstSupply

cache,updateState, updateInterestRates were explained in the common functions section.

validateSupply

In validateSupply, two key checks are being executed:

1. check asset status: ensure ACTIVE & ensure NOT FROZEN & NOT PAUSED

2. check supply cap: ensure it is not exceeded by this new supply action

getFlags

Function takes ReserveConfigurationMap struct as parameter. ReserveConfigurationMap contains data, which is a bitmap, and the various status flags range from bit 56 to 60.

• For in-depth explanation: see getFlags

• Execution reverts if any of the following conditions are TRUE:

  • asset is not ACTIVE

  • asset is PAUSED

  • asset is FROZED

Check supply cap

The long require statement simply means:

require(supplyCap == 0 || newSupply <= supplyCap)

• if supplyCap == 0, require statement clears (unlimited supply allowed)

• if newSupply <= supplyCap, require statement clears

The easier (less-gas intensive) check is placed first, to allow early reversion thereby saving gas on wasted calculations.

getSupplyCap

uint256 internal constant SUPPLY_CAP_START_BIT_POSITION = 116
uint256 internal constant SUPPLY_CAP_MASK = 0xFFFFFFFFFFFFFFFFFFFFFFFFFF000000000FFFFFFFFFFFFFFFFFFFFFFFFFFFFF;

• Only bits 116 - 151 are set to 0 in the mask; these bits will be set to 1 after the ~ operation.

• data & ~SUPPLY_CAP_MASK will return a hexadecimal number in which all the characters are set to 0,except potentially the bits representing the supply cap.

• These bits will return the hex value of the supply cap.

• If supply cap is indeed 0, then 0x000...000 would be returned.

Numbers in Solidity are left-padded. Therefore to convert our resulting hexadecimal number to the appropriate number representation so that it can be cast as a uint256, right shifting by 116 bits is required.

• this will remove all the 0s on the right, from the least significant bit to the value

• left-padding will be done accordingly, to ensure 32 byte representation

See a more in-depth walkthrough of this process at getReserveFactor.

newSupply

// newSupply: currentSupply + amount
AToken.scaledTotalSupply + [accruedToTreasury * nextLiquidityIndex] + amount

• amount is the incoming injection of deposits

• AToken.scaledTotalSupply represents supply held only by suppliers

• Need to account for treasury portion separately as Treasury's ATokens are not minted, just numerically tracked as we saw in .updateState