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???
08/21/06 21:46
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 		 #122742 - Jump TABLE
Responding to: ???'s previous message
Erik Malund said:
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           mov   a,BSNCcost            ;get color
           mov   dptr,#BSNjcol
           jmp   @a+dptr
                       
BSNjcol:   sjmp  BSNr2                 ; read 1/2 time 
           sjmp  BSNr4
           sjmp  BSNr8
            ; etc

That's a computed goto.
This:
Save This Code
        mov    a,BSNCcost;
        mov    dptr,#TableBase;
        movc   a,@a+dptr
        push   a;
        mov    a,BSNCcost;
        inc    dptr;
        movc   a,@a+dptr
        push   a;
        ret;          call routine pointed to by table
        ; return here
TableBase:
        dw, addrBSNr2;
        dw, addrBSNr4;
        dw, addrBSNr8;
        ; etc

That's the equivalent table driven version. I expect for many case statements the compiler can 'optimise' this further by just looking up the LS byte of the address provided the code sits within a 256 byte page.

Ian




List of 38 messages in thread
TopicAuthorDate
Switch/Case and code protection            01/01/70 00:00      
   What does it do?            01/01/70 00:00      
      I activate MOVC Disable.            01/01/70 00:00      
         In that case ...            01/01/70 00:00      
            Can't tell...uses external CCASE routine            01/01/70 00:00      
               Things you can and can't do ...            01/01/70 00:00      
                  it does            01/01/70 00:00      
               (double post, please disregard)            01/01/70 00:00      
   switch can use MOVC instructions            01/01/70 00:00      
      Aha!            01/01/70 00:00      
         protecting LPC chips            01/01/70 00:00      
            protecting LPC chips            01/01/70 00:00      
               Old question            01/01/70 00:00      
                  case            01/01/70 00:00      
                     Errr...            01/01/70 00:00      
                        There is more than just switch/case            01/01/70 00:00      
                           No C without MOVC            01/01/70 00:00      
                              Protection on other derivatives            01/01/70 00:00      
                                 Example - AT89C51            01/01/70 00:00      
                                    AT89C51 can do MOVC internal !            01/01/70 00:00      
                                       nope            01/01/70 00:00      
            LPC Protection            01/01/70 00:00      
               naah, but make it quite a bit more difficult            01/01/70 00:00      
   Compiler Optimisation            01/01/70 00:00      
      sure, but there will still be MOVC            01/01/70 00:00      
         And upgrading the compiler can change the output            01/01/70 00:00      
            the ICEman cometh            01/01/70 00:00      
               I have found no issues with the ICE            01/01/70 00:00      
                  sure it 'works'            01/01/70 00:00      
         The Reason            01/01/70 00:00      
            no, no, no            01/01/70 00:00      
               But you said..            01/01/70 00:00      
                  if you heard what I thought I said            01/01/70 00:00      
                     Confused            01/01/70 00:00      
                        jmp @dptr is not movc            01/01/70 00:00      
                           jmp @dptr is a computed goto not a jump table            01/01/70 00:00      
   what requires a movc???            01/01/70 00:00      
      Jump TABLE            01/01/70 00:00      

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