In addition to maximal-length sequences, liquid also implements complementary codes: P/N sequence pairs which have similar properties to m-sequences. A complementary code pair is one in which the sum of individual auto-correlations is identically zero for all delays except for the zero-delay which provides an auto-correlation of unity.

http://liquidsdr.org/doc/ccodes/

This tutorial explains how to write and simulate a phase-locked loop in the C programming language.

http://liquidsdr.org/blog/pll-howto/

A super simple phase-locked loop in 50 lines of C.

http://liquidsdr.org/blog/pll-simple-howto/