SNES LoROM Address <-> PC Address Conversion script

;----------------------------------------------------------
; SNES LoRom -> PcAddress conversion
;
;   You must set 2 labels:
;     - BEGIN ROM (LABEL 1021)
;     - END ROM (LABEL 1022)
;
;   [Usage]
;     - SNES Addr -> PC Addr -
;     m     #addr    w0
;     bra   820
;     ; you can get pc addr from w0
;
;     - PC Addr -> SNES Addr -
;     m     #addr    w0
;     bra   830
;     ; you can get snes addr from w0
;
;----------------------------------------------------------

;---------------------------------------
; SNES Addr -> PC Addr
;---------------------------------------
:820
  bra 822 ; header check
  r0

  m   w0            w1
  n   #0x7fff     & w1
  n   #0x7f0000   & w0
  n   #1          > w0
  n   w1          | w0
  c   #0            w4
  beq 821
  a   #0x200        w0
:821
  r

;--- header include check sub routine
:822
  ; header include check
  m   l1022         w4
  s   l1021         w4
  n   #0x8000     $ w4
  r

;---------------------------------------
; PC Addr -> SNES Addr
;---------------------------------------
:830
  bra 822 ; header check
  r0

  c   #0            w4
  beq 831
  s   #0x200        w0
:831
  m   w0            w1
  n   #0x7fff     & w1
  n   #0x8000     | w1
  n   #1          < w0
  n   #0x7f0000   & w0
  n   w1          | w0
  r