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%codegen.m generates one of the 32 C/A codes  
function [ca_used]=codegen(svnum) 
 
%ca_used: a vector containing CA code sequence bit stream 
%the g2s vector holds the appropriate shift of the G2 code  
%generate the C/A code (ex. for SV#19-use G2 shift of G2S(19)=471) 
%svnum: satellite number 
 
g2s=[ 5  ;  6;  7;  8; 17; 18;139;140; 
      141;251;252;254;255;256;257;258; 
      469;470;471;472;473;474;509;512; 
      513;514;515;516;859;860;861;862]; 
g2shift = g2s(svnum,1); 
 
%*******generate G1 code*************** 
 
  reg = -1*ones(1,10); 
  for i=1:1023 
     g1(i)=reg(10); 
     save1=reg(3)*reg(10); 
     reg(1,2:10)=reg(1:1:9); 
     reg(1)=save1; 
  end 
%********generate G2 code************** 
 
  reg = -1*ones(1,10); 
  for i= 1:1023 
     g2(i)=reg(10); 
     save2=reg(2)*reg(3)*reg(6)*reg(8)*reg(9)*reg(10); 
     reg(1,2:10)=reg(1:1:9); 
     reg(1)=save2; 
  end 
   
%********shift G2 code**************** 
   
  g2tmp(1,1:g2shift)=g2(1,1023-g2shift+1:1023); 
  g2tmp(1,g2shift+1:1023)=g2(1,1:1023-g2shift); 
  g2=g2tmp; 
   
%generate C/A code sample by multipying G1 and G2 
   
 ca_used=g1.*g2;