MEMSWAP
         PLA
         STA   RETADR
         PLA
         STA   RETADR+1
         PLA
         STA   :LENGTH
         PLA
         STA   ADDR1
         STA   :A1
         PLA
         STA   ADDR1+1
         STA   :A1+1
         PLA
         STA   ADDR2
         STA   :A2
         PLA
         STA   ADDR2+1
         STA   :A2+1
         LDA   ERRCTRL
         CMP   #1
         BEQ   :CHKERR
         JMP   :ERREND
:CHKERR
         LDA   ADDR2+1    
         CMP   ADDR1+1
         BCS   :CHKLO     
         JMP   :A1GTA2    
:CHKLO
         LDA   ADDR2
         CMP   ADDR1
         BCS   :A2GTA1
         JMP   :A1GTA2
:A2GTA1
         LDA   ADDR2      ;CALC DEST-SRC
         SEC
         SBC   ADDR1
         TAX
         LDA   ADDR2+1
         SBC   ADDR1+1    
                          
         TAY
         TXA   
         CMP   :LENGTH
         TYA
         SBC   :LENGTH+1
         BCS   :ERREND    
         JMP   :OVF
:A1GTA2
         LDA   ADDR1
         SEC
         SBC   ADDR2
         TAX
         LDA   ADDR1+1
         SBC   ADDR2+1
         TAY
         TXA
         CMP   :LENGTH
         TYA
         SBC   :LENGTH+1
         BCS   :ERREND
:OVF
         _ERR  #:E_SID;#:E_OVF;#:E_DUMP;#:LENGTH;#6
:ERREND
         LDY   #255       
:LP
         INY
         LDA   (ADDR1),Y
         TAX   
         LDA   (ADDR2),Y  
         STA   (ADDR1),Y
         TXA
         STA   (ADDR2),Y
         CPY   :LENGTH
         BNE   :LP
         LDA   RETADR+1
         PHA
         LDA   RETADR
         PHA
         RTS
:LENGTH  DS    2
:A1      DS    2
:A2      DS    2
:E_SID   ASC   "MEMSWAP (MSWAP MACRO)",00
:E_DUMP  ASC   "DUMPING LENGTH (2) A1(2) A2(2)",00
:E_OVF   ASC   "OVERFLOW! ADDRESSES OVERLAP.",00