BlockLevel returns the block level of the given header.

CheckProofOfWorkByBits check's if the block has a valid PoW according to its Bits field it does not check if the difficulty itself is valid or less than the maximum for the appropriate network.

NewState creates a new state with pre-computed values to speed up mining It takes the target from the Bits field.

State is an intermediate data structure with pre-computed values to speed up mining.