xDai bridged from xDai to Ethereum: Bridge requests from xDai to Ethereum use the Dai in the reserve. If a request is initiated that exceeds the available reserve amount, the requested amount exceeding the reserve + 1,000,000 Dai (required reserve) is withdrawn immediately from Compound. The 1,000,000 Dai replenishes the reserve.
if current_reserve < requested
withdraw requested - current_reserve + required_reserve