; utility functions for common cases
; (from the caller's perspective, these have the side effect of setting Y,
; since the modify routine will 'save' and 'restore' the value we're setting here)
modify3
         ldy   #$03
         !byte $2C
         ; /!\ execution falls through here
modify2
         ldy   #$02
         !byte $2C
         ; /!\ execution falls through here
modify1
         ldy   #$01
         ; /!\ execution falls through here
;-------------------------------
; modify subroutine
; in:  A = starting address (high byte)
;      X = starting address (low byte)
;      Y = string length
;      stack = string to set
; out  $BASEPAGE buffer changed
;      $gPatchCount++
;      $modsrc zero page clobbered
;      $moddest zero page clobbered
;      stack set to return to
;        code after string
;      A,X,Y preserved
;      oVerflow bit clear
;      all other flags clobbered
;-------------------------------
modify
         sty   mod_tmp_y
         sta   gDisplayBytes
         clc
         adc   #BASEPAGE
         sta   moddest+1
         stx   moddest
         stx   gDisplayBytes+1
         pla
         sta   modsrc
         pla
         sta   modsrc+1
         tax
         tya
         clc
         adc   modsrc
         bcc   +
         inx
+        sta   tmp
         txa
         pha
         lda   tmp
         pha
         sty   modtmp
         bit   gMode
         bpl   @exitnomod            ; verify mode -> no modify
         jsr   PrintByID
         !byte s_modify
         ldy   #0
-        lda   (moddest), y
         jsr   PrintByte
         iny
         cpy   modtmp
         bne   -
         jsr   PrintByID
         !byte s_modifyto
         ldy   #0
-        iny
         lda   (modsrc), y
         jsr   PrintByte
         cpy   modtmp
         bne   -
         lda   #$8D
         jsr   PrintA
         bvc   +
-        sta   (moddest), y
+        lda   (modsrc), y
         dey
         bpl   -
@exit
         inc   gPatchCount
@exitnomod
         lda   gDisplayBytes
         ldx   moddest
mod_tmp_y=*+1
         ldy   #$FD                  ; SMC
         clv
         rts