Some codes need optimization

[gzliudan]

I found this library from a third contract. And maybe some codes can be optimized to save gas. For example: xc > 0x1 is better than xc >= 0x2. In Solidity, there is no single op-code for ≤ or ≥ expressions. Solidity compiler executes the LT/GT (less than/greater than) op-code and afterwards it executes an ISZERO op-code to check if the result of the previous comparison (LT/ GT) is zero and validate it or not. So the use of < and > are cheaper than ≤ and ≥.

[3sGgpQ8H]

This should probably be reported to the Solidity team, as compiler should know how to use the available opcodes in the most efficient way.