CRC problem

Good morning.
I have problem with CRC. Math.lib has getcrc, but this function uses 1021 polynom without reverse initial data bytes and without reverse CRC result.
I need two functions for CRC: CRC-CCITT (polynom 1021) with reverse initial data bytes and reverse CRc result and CRC16 (polynom 8005) with reverse initial data bytes and reverse CRc result, too. How can i implement these functions? Are there other libraries with this implementations?

Thank you so much.

Aldrin