10 REM 'CHANGE'
   20 REM An experimental program for    altering Machine Code programs to run   at a different location.
   30 MODE7
   40 ON ERROR PROCerror:END
   50 PRINT CHR$(141);" ALTCODE - Changes Program addresses"
   60 PRINT CHR$(141);" ALTCODE - Changes Program addresses"
   70  PRINT'"   The addresses are changed but the       machine code program is not moved.     Program must be *SAVEd and reloaded        at the new address before use."
   80 VDU28,0,24,39,8,12
   90 INPUT"Enter actual starting address &"B$
  100 INPUT'"Enter actual finishing address &"C$
  110 B=EVAL("&"+B$)
  120 IF C$>B$ C=EVAL("&"+C$):D=C-B+1 ELSE VDU7:PRINT'"Finishing address must be higher than   the starting address, please re-enter   details":wait=TIME:REPEAT UNTIL(TIME-wait)>400:GOTO80
  130 INPUT'"Enter starting address where code shouldnormally reside &"E$
  140 E=EVAL("&"+E$):F=E+D
  150 INPUT'"Enter the new starting address &"G$
  160 G=EVAL("&"+G$)
  170 IF G>E H=G-E:?&7A=0 ELSE H=E-G:?&7A=&FF
  180 ?&70=B MOD &100:?&71=B DIV &100
  190 ?&72=D MOD &100:?&73=D DIV &100
  200 ?&74=E DIV &100:?&75=F DIV &100
  210 ?&78=H MOD &100:?&79=H DIV &100
  220 RESTORE 1340 :REM 6502 CPU
  230 REM RESTORE 1400 :REM 6512 CPU
  240 FOR word=&A00 TO &AFC STEP 4
  250 READ number%
  260 !word=number%
  270 NEXT
  280 :
  290 PROCcode
  300 CALL&900
  310 result=?&77*256+?&76
  320 PRINT'"There were ";result;" addresses changed."
  330 VDU7
  340 C=C+1:C$=STR$~(C)
  350 PRINT'" *SAVE XXXX ";B$;" ";C$;" ";G$;" ";G$
  360 PRINT'"Code may be saved by copying the above  line, using the up arrow and COPY keys."
  370 END
  380 :
  390 DEF PROCcode
  400 searchbase=&70:memtotal=&72
  410 counter=&76   :REM number of alterations counter
  420 FOR pass=0 TO 2 STEP 2
  430 P%=&900
  440 [OPT pass
  450 INC &75
  460 LDY #0
  470 STY &76
  480 STY &77
  490 LDA memtotal+1  \checking machine code program
  500 BEQ nohigh
  510 .loop1
  520 JSR compare
  530 LDA memtotal+1
  540 BNE loop1
  550 .nohigh
  560 LDA memtotal
  570 BEQ done
  580 .loop2
  590 JSR compare
  600 CPY memtotal
  610 BCC loop2
  620 .done
  630 RTS
  640 :
  650 .compare
  660 LDA (searchbase),Y
  670 TAX
  680 LDA &A00,X
  690 TAX
  700 CPX #3
  710 BEQ change
  720 .skip  \1 & 2 byte Opcodes, no action taken
  730 JSR update
  740 DEX
  750 BNE skip
  760 RTS
  770 :
  780 .change  \check to see whether address is within the program area
  790 JSR update
  800 JSR update
  810 LDA (searchbase),Y   \check address (hi byte)
  820 CMP &74
  830 BCC out
  840 CMP &75
  850 BCS out
  860 INC counter   \increment address change counter
  870 BNE few
  880 INC counter+1
  890 .few
  900 DEY
  910 CPY #&FF
  920 BNE jump
  930 DEC searchbase+1
  940 INC memtotal+1
  950 .jump
  960 LDA &7A  \check to see if move should be up or down
  970 BNE down
  980 :
  990 .up  \alter address up or down as appropriate
 1000 CLC
 1010 LDA (searchbase),Y
 1020 ADC &78
 1030 STA (searchbase),Y
 1040 JSR update
 1050 LDA (searchbase),Y
 1060 ADC &79
 1070 STA (searchbase),Y
 1080 JMP out
 1090 :
 1100 .down
 1110 SEC
 1120 LDA (searchbase),Y
 1130 SBC &78
 1140 STA (searchbase),Y
 1150 JSR update
 1160 LDA (searchbase),Y
 1170 SBC &79
 1180 STA (searchbase),Y
 1190 .out
 1200 JSR update
 1210 RTS
 1220 :
 1230 .update \increment Y register counter
 1240 INY
 1250 BNE over
 1260 INC searchbase+1
 1270 DEC memtotal+1
 1280 .over
 1290 RTS
 1300 ]:NEXT
 1310 ENDPROC
 1320 :
 1330 REM 6502 CPU Opcode bytes
 1340 DATA &01010201,&01020201,&01010201,&01030301,&01010202,&01020201,&01010301,&01030301,&01010203,&01020202,&01010201,&01030303,&01010202,&01020201,&01010301,&01030301
 1350 DATA &01010201,&01020201,&01010201,&01030303,&01010202,&01020201,&01010301,&01030301,&01010201,&01020201,&01010201,&01030303,&01010202,&01020201,&01010301,&01030301
 1360 DATA &01010201,&01020202,&01010101,&01030303,&01010202,&01020202,&01010301,&01010301,&01020202,&01020202,&01010201,&01030303,&01010202,&01020202,&01010301,&01030303
 1370 DATA &01010202,&01020202,&01010201,&01030303,&01010202,&01020201,&01010301,&01030301,&01010202,&01020202,&01010201,&01030303,&01010202,&01020201,&01010301,&01030301
 1380 :
 1390 REM 6512 CPU Opcode bytes
 1400 DATA &01010201,&01020202,&01010201,&01030303,&01020202,&01020202,&01010301,&01030303,&01010203,&01020202,&01010201,&01030303,&01020202,&01020202,&01010301,&01030303
 1410 DATA &01010201,&01020201,&01010201,&01030303,&01020202,&01020201,&01010301,&01030301,&01010201,&01020202,&01010201,&01030303,&01020202,&01020202,&01010301,&01030302
 1420 DATA &01010202,&01020202,&01010201,&01030303,&01020202,&01020202,&01010301,&01030303,&01020202,&01020202,&01010201,&01030303,&01020202,&01020202,&01010301,&01030303
 1430 DATA &01010202,&01020202,&01010201,&01030303,&01020202,&01020201,&01010301,&01030301,&01010202,&01020202,&01010201,&01030303,&01020202,&01020201,&01010301,&01030301
 1440 :
 1450 DEF PROCerror
 1460 REPORT:PRINT" at line ";ERL
 1470 ENDPROC