https://github.com/code-423n4/2024-03-phala-network/blob/a01ffbe992560d8d0f17deadfb9b9a2bed38377e/phala-blockchain/crates/pink/runtime/src/contract.rs#L122-L135
The function coarse gas relies on complex bit math to mask deposits in order to mitigate side channel attacks. Therefore, we can consider that masked deposits must be at least higher or equal to the original deposit. However, this invariant can be broken.
Consider the fuzz test below:
Here the invariant will be broken if deposit_per_byte is = 664613997892457936451903530140172289. This can be problematic if the cluster creator (the actor who sets the deposit per byte) is acting in a malicious way as this opens the door for the side channel attack that the function is supposed to prevent. 
