addsub and subadd are used to add and subtract binary numbers there are two ways
(1) that you deal with 2's complement so when you add or subtract it will easy
(2) the way that i add asign and didnt use 2's complement it works by comparison so if A is positive and B is positive so A+B is (A+B) without the sign and sign is +ve
if A is -ve and B is -ve so A+B is (A+B) without sign and sign is -ve
if A is +ve and B is -ve and A>B so A+B is (A-B) without sign and sign is +ve
if A is +ve and B is -ve and A<B so A+B is (B-A) without sign and sign is -ve
and so on i hope you got it (i made it at that way because i have that code before but you can make 2's complement this is the link
https://en.wikipedia.org/wiki/Two's_complement)
- - - Updated - - -
epsi function is a lookup table to calculate tanh-1(|X|/2)
this link contain a thesis for an LDPC DVB-S2 project i hope it helps
http://www.google.com.eg/url?sa=t&rct=j&q=MSc_thesis_draft_sept_20_2010&source=web&cd=1&cad=rja&ved=0CCkQFjAA&url=http%3A%2F%2Fecommons.usask.ca%2Fbitstream%2Fhandle%2F10388%2Fetd-09222010-114940%2FMSc_thesis_draft_sept_20_2010.pdf&ei=rywCUs3DH4PetAaFuoGAAQ&usg=AFQjCNG3sKatHhTaraFJow5wL_s-edtiWA&bvm=bv.50310824,d.Yms
- - - Updated - - -
epsi function is a lookup table to calculate tanh-1(|X|/2)
this link contain a thesis for an LDPC DVB-S2 project i hope it helps
http://www.google.com.eg/url?sa=t&rct=j&q=MSc_thesis_draft_sept_20_2010&source=web&cd=1&cad=rja&ved=0CCkQFjAA&url=http%3A%2F%2Fecommons.usask.ca%2Fbitstream%2Fhandle%2F10388%2Fetd-09222010-114940%2FMSc_thesis_draft_sept_20_2010.pdf&ei=rywCUs3DH4PetAaFuoGAAQ&usg=AFQjCNG3sKatHhTaraFJow5wL_s-edtiWA&bvm=bv.50310824,d.Yms