how to define my own function in my block.tlc?

hello,everyone,i am developing blocks with S-function and tlc files, i need to write my own function in the block.tlc file. i don't know how to write it,can anybody help me ? thanks in advance The block.tlc file is like this:

%implements  mpc5634_sci "C"

%function BlockTypeSetup(block, system) void

   %assign scia_dfm_idx = CAST("Number",SFcnParamSettings.scia_dfm) 

   %assign scib_dfm_idx = CAST("Number",SFcnParamSettings.scib_dfm) 

   %switch scia_dfm_idx
          %case 1
              %assign scia_dfm = 8
              %break
          %case 2
              %assign scia_dfm = 9
              %break
          %case 3
              %assign scia_dfm = 12
              %break
          %case 4
              %assign scia_dfm = 13
              %break
   %endswitch

   %switch scib_dfm_idx
          %case 1
              %assign scib_dfm = 8
              %break
          %case 2
              %assign scib_dfm = 9
              %break
          %case 3
              %assign scib_dfm = 12
              %break
          %case 4
              %assign scib_dfm = 13
              %break
   %endswitch

   %openfile tmp  
/************************SCI***************************************************/

#define SCIA_FORMATMODE_MD (U08)%<scia_dfm>

#define SCIB_FORMATMODE_MD (U08)%<scib_dfm>

   %closefile tmp
   %assign cFile = LibCreateSourceFile("Header", "Custom", "interfunc_cfg")  
   %<LibSetSourceFileSection(cFile, "Defines", tmp)>\  
%endfunction

i want to take the following part out of this function,and define a new function for it. how should i write the function? i've searched it for several times, but i still can't get it.

      %switch scia_dfm_idx
          %case 1
             %assign scia_dfm = 8
              %break
          %case 2
              %assign scia_dfm = 9
              %break
          %case 3
              %assign scia_dfm = 12
              %break
          %case 4
              %assign scia_dfm = 13
              %break
   %endswitch