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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 |
critique d'une petite routine
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Envoyé par bifur
Je voudrais quand même trouver un moyen de passer un byte ou toute valeur plus "légère" qu'un mot sur la pile (et la retrouver sans difficulté ni erreur possible depuis l'intérieur de la routine).
) donc le décalage dans la pile varie en fonction de la façon dont on appelle la sous fonction
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