Utility routines: SWAPPZERO

       Name: SWAPPZERO                                               [Show more]
       Type: Subroutine
   Category: Utility routines
    Summary: A routine that swaps zero page with the page at $CE00, so that
             zero page changes made by Kernal functions can be reversed
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * KERNALSETUP calls SWAPPZERO
             * LOD calls SWAPPZERO
             * SVE calls SWAPPZERO


IF _GMA_RELEASE

.SWAPPZERO

 LDX #K3+1              ; This routine starts copying zero page from $0015 and
                        ; up, using X as an index

.SWPZL

 LDA ZP,X               ; Swap the X-th byte of zero page with the X-th byte of
 LDY $CE00,X            ; $CE00
 STA $CE00,X
 STY ZP,X

 INX                    ; Increment the loop counter

 BNE SWPZL              ; Loop back for the next byte

 RTS                    ; Return from the subroutine

ENDIF