rdos/lib/printf.asm

printf:
  cld
  pop si
  push bp
  mov bp, sp
.loop:
  mov al, [cs:si]
  inc si
  cmp al, 0x00
  je .end
  cmp al, 0x25
  je .handle_25h
.literal:
  call putc
  jmp .loop
.end:
  pop bp
  push si
  ret
.handle_25h:
  mov al, [cs:si]
  inc si
  cmp al, 0x25
  je .literal
  cmp al, 0x58 ; 'X'
  je .printhex
  cmp al, 0x55 ; 'U'
  je .printdec
  cmp al, 0x53 ; 'S'
  je .printstr
  mov al, 0x3F
  jmp .literal
.printhex:
  add bp, 2
  mov ax, [bp]
  mov bx, 0x0010
  call print_number
  jmp .loop
.printdec:
  add bp, 2
  mov ax, [bp]
  mov bx, 0x000A
  call print_number
  jmp .loop
.printstr:
  add bp, 2
  mov ax, [bp]
  call print_string
  jmp .loop

; converts a integer to ascii
; in    ax      input integer
;       bx      base
;	cx	minimum number of digits
; out   bx      garbled
;       dx      garbled
print_number_padded:
  xor dx, dx
  div bx
  push dx
  dec cx
  jz .nopad
  call print_number_padded
  jmp print_number.end
.nopad:
  call print_number
  jmp print_number.end

; converts a integer to ascii
; in	ax	input integer
;	bx	base
; out	bx	garbled
;	dx	garbled
print_number:
  xor dx, dx
  div bx ; ax = dx:ax / 10, dx = dx:ax % 10
  push dx
  and ax, ax
  jz .end
  call print_number
.end:
  pop bx
  xor bh, bh
  add bx, print_chars
  mov al, [cs:bx]
  call putc
  ret

; putc's a string
; in	DS:AX	null-terminated string
print_string:
  push si
  mov si, ax
.loop:
  lodsb
  cmp al, 0x00
  je .end
  call putc
  jmp .loop
.end:
  pop si
  ret

print_chars:
  db "0123456789ABCDEF"