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08/06/07 19:08
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 		 #142830 - CRC16 CCITT - What a challenge!
I couldn not resist, sat down and polished the "algorithmic" solution for the CCITT CRC-16 (0x1021 "direct", left shifting ("normal" bit order)) a bit more.

Now, it is 22 cycles, compared to 14 for the table based (I tweaked the latter, too); giving up one RAM byte (I (ab)used B) and carry. The code space consumption is uncomparable.

This makes the use of the table version highly questionable; whereas C-based implementations are a bad joke since today (except for Russ, who apparently does not value execution speed in embedded mcu-s too much ;-) ).

Both implementations are in the code library (look for CRC16 - what did you expect? :-) )

Now, beat me if you can! :-)

JW


List of 32 messages in thread
TopicAuthorDate
CRC16 CCITT - What a challenge!            01/01/70 00:00      
   Have you seen this?            01/01/70 00:00      
      Of course!            01/01/70 00:00      
         Balance            01/01/70 00:00      
            I know, Russ,            01/01/70 00:00      
         Code? What code?            01/01/70 00:00      
            in the code library - look to the left column            01/01/70 00:00      
               Thanks! I missed that note in the first post.            01/01/70 00:00      
   I need a hint            01/01/70 00:00      
      write down the bits            01/01/70 00:00      
         Thanks for the hint            01/01/70 00:00      
            Your observations plus a comparison in C            01/01/70 00:00      
               The rest of the story ...            01/01/70 00:00      
                  Compilers, but Keil C51 8.09 for the stated 28~            01/01/70 00:00      
                  and this processes only a nibble, isn't it...            01/01/70 00:00      
                     No, it process the entire byte.            01/01/70 00:00      
                        now it\'s my pencil time...            01/01/70 00:00      
                           FYFI            01/01/70 00:00      
                              Clarification re: 8-bit optimized term            01/01/70 00:00      
                              on optimisation            01/01/70 00:00      
                                 Jan's optimization            01/01/70 00:00      
                                    Re: on optimization            01/01/70 00:00      
                                       Can you please be more specific?            01/01/70 00:00      
                                          More specifically ...            01/01/70 00:00      
            and what            01/01/70 00:00      
               More on checksums            01/01/70 00:00      
   No reason to hide the excreted code            01/01/70 00:00      
      Excreted code needs context like any other code            01/01/70 00:00      
   One More Comment            01/01/70 00:00      
      ... and a marginal remark ...            01/01/70 00:00      
         Init all ones frequently specified            01/01/70 00:00      
   18 cycles            01/01/70 00:00      

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