680x0:Opening a library

From Amiga Coding

This is a example on how to open a library:
(with the Library Vector Offsets added so you won't need to use any includes yet)

OldOpenLibrary	= -408		; OldOpenLibrary(libName)(A1)
OpenLibrary	= -552		; OpenLibrary(libName,version)(A1,D0)
CloseLibrary	= -414		; CloseLibrary(library)(A1)
 
	move.l	$4.w,a6		; Get the value at position $4 in memory
				; This value is the base of exec.library
 
	lea	LibName(pc),a1	; libName must be in A1
	moveq	#0,d0		; version must be in D0
	jsr	OpenLibrary(a6)	; Call the OpenLibrary function
 
	; OpenLibrary looks if the library is in memory (or ROM)
	; and loads it if nessesary.
	; Then it returns the base of the requested library in d0
 
	move.l	d0,libbase	; Store the base
 
 
	; You can access function in a library with this base,
	; like we called OpenLibrary() with exec.library's base.
;	move.l  d0,a6           ; move to a6, since d0 can't be used for addresses
;	jsr     SomeFunction(a6)
 
 
	; Now close the library we opened
	move.l  $4.w,a6         ; Get exec.library's base again
	move.l	libbase,a1	; Get the base of the library we want to close
	jsr	CloseLibrary(a6)
 
	rts
 
libname:	dc.b	'dos.library',0
libbase:	dc.l	$00000000

Notes (important):

• ...a6
• ...scratch registers

Notes on optimizing:

• • use 'move.l $4.w,a6' instead of 'move.l $4,a6'
  • use 'moveq' if the version you require is lower than 128
  • if you want to save on bytes you can reuse libname to store your libbase
  • There's also a function OldOpenLibrary doesn't have the library version check. If you are desperate you could use OldOpenLibrary and save a few bytes by not needing a moveq/move.l #version,d0. Commodore didn't want anyone to use this, it would be removed, but it never happened and removing it would probably break too many programs.

LVO's

TODO