print.s

   1 %define CURRENT_ADDR cs:di
   2
   3 ; Prints a null terminated string of your choice.
   4 ; Arguments:
   5 ;     CS:DI - pointer to the string you want to print
   6 print:
   7         pusha
   8         mov ah, 0Eh ; teletype print
   9 .write2:
  10         mov al, [CURRENT_ADDR] ; get current char and put it in al
  11         cmp al, 0 ; check if al is null (string terminator)
  12         je .done ; if it is, start a new line
  13         int 10h ; otherwise write the char
  14         inc di ; increment pointer to string
  15         jmp .write2 ; jump back to this section
  16 .done:
  17         mov al, 0Dh ; carriage return
  18         int 10h
  19         mov al, 0Ah ; line feed
  20         int 10h
  21         popa
  22         ret ; return
  23
  24 ; Prints a word (16-bit value) in hex format.
  25 ; Arguments:
  26 ;     DX - word to print
  27 print_word:
  28         pusha ; push all regs to stack
  29         mov di, HEX_OUT+5 ; set destination index to last char in HEX_OUT
  30         mov ax, dx ; copy argument to accumulator
  31         and al, 00001111b ; extract the low nibble of the low half of the accumulator
  32         call .compare ; fill in the string with correct value
  33         dec di ; decrement string pointer
  34         mov ax, dx ; copy argument to accumulator
  35         and al, 11110000b ; extract high nibble of low half of accumulator
  36         shr al, 4 ; shift high nibble to low nibble
  37         call .compare ; fill in string with correct value
  38         dec di
  39         mov al, ah ; copy high portion of accumulator to low
  40         and al, 00001111b ;
  41         call .compare
  42         dec di
  43         mov al, ah
  44         and al, 11110000b
  45         shr al, 4
  46         call .compare
  47         mov di, HEX_OUT
  48         call print ; write string
  49         popa
  50         ret
  51
  52 .compare:
  53         cmp al, 0 ; compare al with 0
  54         jne .one ; if not equal, compare with 1
  55         mov byte [CURRENT_ADDR], '0' ; set character to ASCII 0
  56         ret ; return
  57 .one:
  58         cmp al, 1
  59         jne .two
  60         mov byte [CURRENT_ADDR], '1'
  61         ret
  62 .two:
  63         cmp al, 2
  64         jne .three
  65         mov byte [CURRENT_ADDR], '2'
  66         ret
  67 .three:
  68         cmp al, 3
  69         jne .four
  70         mov byte [CURRENT_ADDR], '3'
  71         ret
  72 .four:
  73         cmp al, 4
  74         jne .five
  75         mov byte [CURRENT_ADDR], '4'
  76         ret
  77 .five:
  78         cmp al, 5
  79         jne .six
  80         mov byte [CURRENT_ADDR], '5'
  81         ret
  82 .six:
  83         cmp al, 6
  84         jne .seven
  85         mov byte [CURRENT_ADDR], '6'
  86         ret
  87 .seven:
  88         cmp al, 7
  89         jne .eight
  90         mov byte [CURRENT_ADDR], '7'
  91         ret
  92 .eight:
  93         cmp al, 8
  94         jne .nine
  95         mov byte [CURRENT_ADDR], '8'
  96         ret
  97 .nine:
  98         cmp al, 9
  99         jne .ten
 100         mov byte [CURRENT_ADDR], '9'
 101         ret
 102 .ten:
 103         cmp al, 0Ah
 104         jne .eleven
 105         mov byte [CURRENT_ADDR], 'A'
 106         ret
 107 .eleven:
 108         cmp al, 0Bh
 109         jne .twelve
 110         mov byte [CURRENT_ADDR], 'B'
 111         ret
 112 .twelve:
 113         cmp al, 0Ch
 114         jne .thirteen
 115         mov byte [CURRENT_ADDR], 'C'
 116         ret
 117 .thirteen:
 118         cmp al, 0Dh
 119         jne .fourteen
 120         mov byte [CURRENT_ADDR], 'D'
 121         ret
 122 .fourteen:
 123         cmp al, 0Eh
 124         jne .fifteen
 125         mov byte [CURRENT_ADDR], 'E'
 126         ret
 127 .fifteen:
 128         mov byte [CURRENT_ADDR], 'F'
 129         ret
 130
 131 HEX_OUT: db "0x0000", 0