Question

This code below takes in an two digit number (let’s say 12) in ASCII and should return this number as the number 12. (NOT ASCII)

mov     $IBUFF, %eax    # IBUFF stores the ASCII number 12
movl    $NUMBER, %ecx   # NUMBER will i put the number 12 (NO ASCII)

movb    (%eax), %bl     # Moves the first byte (1) to %bl
subb    $48, %bl        # Decrease %bl so it is not longer a ASCII sign.
movb    %bl, (%ecx)     # Moves this byte into the first place in NUMBER

inc %eax                # Increase IBUFF so it points to the next integer 
inc %ecx                # Increase NUMBER so it points to the next empty space

movb    (%eax), %bl     # Same as above
subb    $48, %bl        # Same as above
movb    %bl, (%ecx)     # Same as above


mov NUMBER, %eax        # Move the number 12 from NUMBER to %eax (return register)

When i run this code the return value is 513, not 12. What am i doing wrong?

Answer 1

You need to accumulate the result (possibly in a register) by multiplying it by 10, and then adding the new digit. Basic base 10 representation. What you’re doing ends up storing the resulting digits in base 256.