cc65/libsrc/common/sprintf.s

;
; int sprintf (char* buf, const char* Format, ...);
;
; Ullrich von Bassewitz, 1.12.2000
;

        .export         _sprintf
        .import         pushax, addysp, decsp4, _vsprintf
        .importzp       sp, ptr1

        .macpack        generic

; ----------------------------------------------------------------------------
; Data

.bss

ParamSize:      .res    1               ; Number of parameter bytes

; ----------------------------------------------------------------------------
; Code

.code


_sprintf:
        sty     ParamSize               ; Number of param bytes passed in Y

; We have to push buf and format, both in the order they already have on stack.
; To make this somewhat more efficient, we will create space on the stack and
; then do a copy of the complete block instead of pushing each parameter
; separately. Since the size of the arguments passed is the same as the size
; of the fixed arguments, this will allow us to calculate the pointer to the
; fixed size arguments easier (they're just ParamSize bytes away).

        jsr     decsp4

; Calculate a pointer to the Format argument

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

; Now copy both, buf and format

        ldy     #4-1
@L2:    lda     (ptr1),y
        sta     (sp),y
        dey
        bpl     @L2

; Load va_list (last and __fastcall__ parameter to vsprintf)

        lda     ptr1
        ldx     ptr1+1

; Call vsprintf

        jsr     _vsprintf

; Cleanup the stack. We will return what we got from vsprintf

        ldy     ParamSize
        jmp     addysp