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|
; asm (nasm)
; -----------------------------------------------------------------------------
; write_digit
;
; This function is able to write a digit in any numeral base from 2 to 36.
; For bases above 10, it uses latin letters --as for ordinary hex writing.
; Only uppercase letters are used here (they have the size of decimal digits).
; Note that base 36 means digits from 0 to 35, not 36 ;-).
; The only parameter is the digit's numeric value, which should be passed in
; eax (al in fact). The function returns in ebx 0 if all is right, 1 if the
; value was strictly above 35, in which case '?' is written out.
; -----------------------------------------------------------------------------
section .data
; space & newline, for testing
space db 32
newline db 10
; static array of digits, plus error code
digits: db "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ?"
digit_error_code equ $ - 1
section .bss
section .text
global _start
; === write digit =============================================================
; digit numeric value: in al
write_digit:
movzx ecx, al ; pointer to digit will be in ecx for writing
cmp ecx, 35
ja write_digit_above_35
; case below or equal to 35:
mov ebx, 0 ; return value: ok
add ecx, digits ; point to digit
jmp write_digit_write
; case above 35:
write_digit_above_35:
mov ebx, 1 ; return value: error
mov ecx, digit_error_code ; point to error code '?'
; write digit
write_digit_write:
mov edx, 1 ; weight of string to be written
; (pointer to byte already in ecx)
mov ebx, 1 ; file descriptor for stdout
mov eax, 4 ; code for sys_write
int 80h
ret
; === test with sample values =================================================
; --- test tool routines: write space & newline -------------------------------
write_space:
mov edx, 1
mov ecx, space
mov ebx, 1
mov eax, 4
int 80h
ret
write_newline:
mov edx, 1
mov ecx, newline
mov ebx, 1
mov eax, 4
int 80h
ret
; --- start = test ------------------------------------------------------------
_start:
xor eax, eax
; 0
mov al, 0
call write_digit
call write_space
; 1
mov al, 1
call write_digit
call write_space
; 9
mov al, 9
call write_digit
call write_space
; 10
mov al, 10
call write_digit
call write_space
; 15
mov al, 15
call write_digit
call write_space
; 16
mov al, 16
call write_digit
call write_space
; 35
mov al, 35
call write_digit
call write_space
; 36
mov al, 36
call write_digit
call write_space
; 255
mov al, 255
call write_digit
call write_space
call write_newline
jmp _end ; useless here, but kept for generality
; --- end ---------------------------------------------------------------------
_end:
mov ebx, 0 ; exit code 0
mov eax, 1 ; code for sys_exit
int 80h |
