cc65/libsrc/common/scanf.s

;
; int scanf(const char* Format, ...);
;
; 2000-12-01, Ullrich von Bassewitz
; 2004-12-31, Greg King
;

        .export		_scanf

        .import		_stdin, pushax, addysp, _vfscanf
        .import		sp:zp, ptr1:zp

        .macpack	generic

; ----------------------------------------------------------------------------
; Code
;
_scanf:
        sty	ArgSize		; Number of argument bytes passed in .Y

; We are using a (hopefully) clever trick here to reduce code size.  On entry,
; the stack pointer points to the last pushed argument of the variable
; argument list.  Adding the number of argument bytes, would result in a
; pointer that points _above_ the Format argument.
; Because we have to push stdin anyway, we will do that here, so:
;
;   * we will save the subtraction of 2 (__fixargs__) later;
;   * we will have the address of the Format argument which needs to
;     be pushed next.

        lda	_stdin
        ldx	_stdin+1
        jsr	pushax

; Now, calculate the va_list pointer, which does point to Format.

        lda	sp
        ldx	sp+1
        add	ArgSize
        bcc	@L1
        inx
@L1:    sta	ptr1
        stx	ptr1+1

; Push a copy of Format.

        ldy	#1
        lda	(ptr1),y
        tax
        dey
        lda	(ptr1),y
        jsr	pushax

; Load va_list [last and __fastcall__ argument to vfscanf()].

        lda	ptr1
        ldx	ptr1+1

; Call vfscanf().

        jsr	_vfscanf

; Clean up the stack.  We will return what we got from vfscanf().

        ldy	ArgSize
        jmp	addysp

; ----------------------------------------------------------------------------
; Data
;
        .bss
ArgSize:
        .res	1		; Number of argument bytes