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/ Amiga Format CD 23 / Amiga Format AFCD23 (Feb 1998, Issue 107).iso / +look_here_1st!+ / reader_requests / pseudo13 / romchksum.s < prev   
Text File  |  1997-11-28  |  1KB  |  31 lines
  1. *****************************************************************************
  2. *          KICKSTART R2.0+ CHECKSUM CALCULATION                             *
  3. * Compiler: Devpac 3.04                                              ORHAN  *
  4. *****************************************************************************
  5.            MACHINE     MC68000 
  6.            SECTION     "CODE",CODE
  7.  
  8.            LEA.L       ROMEND.L,A0
  9.            CLR.L       ROMCHKSUM(A0) 
  10.            MOVE.L      ROMSIZE(A0),D1
  11.            SUB.L       D1,A0                      ;rom start
  12.            CLR.L       D0
  13. AA0:
  14.            ADD.L       (A0)+,D0
  15.            BCC.S       AA1
  16.            ADD.L       #1,D0
  17. AA1:       SUB.L       #4,D1
  18.            BNE.S       AA0
  19.            NOT.L       D0                         ;checksum
  20.  
  21.            LEA.L       ROMEND.L,A0
  22.            MOVE.L      D0,ROMCHKSUM(A0) 
  23.  
  24.            MOVE.L      #0,D0 
  25.            RTS
  26.  
  27. ROMEND     EQU         $1000000       
  28. ROMCHKSUM  EQU         -$18            
  29. ROMSIZE    EQU         -$14            
  30.            END
  31.