If you are a new auditor and see thefollowing, this might be daunting:
However, there’s no reason to be scared,let’s think about this step by step. In Solidity, a boolean value (bool) takesup a whole storage slot, which is 256 bits, even though it technically onlyneeds a single bit. By using a bitmap, the library packs 256 boolean valuesinto a single uint256 storage slot, greatly optimizing storage usage and,consequently, gas costs for operations. So we have 1 storage slot, which is 32bytes/256 bits and usually we store one boolean in it. However, using theBitMap library, we are able to store 256 booleans into the same storage slot, avery gas-efficient way. This specifically works if we have sequential indexes:0,1,2,3,4 .. 255, as they all are stored in the same storage slot (32bytes).This library looks scary because it is using bit-shifting for that purpose butin fact you simply call the “set” and “unset” functions with the correspondingBitMap storage and the index and then you can fetch the boolean for thecorresponding index using the “get” function. That's really it!
