Clarify the precision of exchangeRate

[axic]

The documentation in https://compound.finance/docs/ctokens#exchange-rate states the following:

However the source code at CToken intialExchangeRateMantissa, CToken and CErc20Delegator states it is fixed at 18 decimal digits.

exchangeRateStoredInternal does not seem to take the underlying asset into account (it uses Exponential.getExp, but that also states 18 decimal precision). Is the documentation just wrong or am I misunderstanding something?

[mijovic]

To make the answer short, documentation is correct here.

To clarify, for the case of DAI/cDAI exchangeRateCurrent() is 28 decimal fixed-point number
18 - 8 + 18 = 28 as in this case Underlying Token Decimals is 18(DAI)

If we read contract here
https://etherscan.io/token/0x5d3a536E4D6DbD6114cc1Ead35777bAB948E3643?a=0x2ec7947f3ac9aaaa44b53640506cdc9d848d9489#readContract

exchangeRateCurrent is 216064523443228187636427149 which has 27 digits so this is 0.021... on 28 decimal precision...

Comments in source code should be fixed