cdma

hi every body this is  shiva newly joined in forum.
i am  doing a project, in which i want to implement the cdma concept in fpga  (i.e., i am taking two message signals,spreaded by two different code sequences ) i am facing probelm at summing up these two sequences.
i am using verilog HDL for coding.
My doubt is how to sum two spreaded squences in fpga.