git.sur5r.net Git - cc65/blob - libsrc/apple2/revers.s

   1         ;;
   2         ;; Kevin Ruland
   3         ;;
   4         ;; unsigned char __fastcall__ revers (unsigned char onoff)
   5         ;;
   6
   7         .export         _revers
   8
   9         .include        "apple2.inc"
  10
  11 _revers:
  12         ldy     INVFLG          ; Stash old value
  13         and     #$FF            ; Test for any bit
  14         beq     normal          ; Nothing set
  15         lda     #~$3F           ; Not Inverse
  16 normal:
  17         eor     #$FF            ; Xor Normal
  18         sta     INVFLG
  19         tya                     ; What was the old value?
  20         eor     #$FF            ; Normal = $FF, Inverse = $3F
  21         beq     L2
  22         lda     #$01
  23 L2:
  24         rts
  25