Re: newbie

Re: newbie

[Fred Marmond]

Hi Niel
string is a label, that's to say here, a pointer.
If you are in x86 architecture (32bits), a pointer is 32bits long, so you'll 
have to do "mov edi,string".
If you are in x86_64 arch (64bits), you'll have to use 64bits registers for 
pointers, "mov rdi,string"


Fred


Le Vendredi 23 Décembre 2005 17:50, Niel A a écrit :
> hello all!
>
> i'm taking linux assembly as a hobby for christmas and i found your great
> site. the tutorials have been much helpful.
>
> anyway, i meant to ask something..
>
> section .data
> 	string: db "hi!",10
>
> and i wanna capitalize the small letter 'h'.
>
> at first i used
> 	mov di, string ; but di is 16 bits and ld complains
>
> so i eventually started using the 32 bit ones to do the capitalisation
> operation. but for some reason, i lose all other letters, including the
> linefeed.
>
> please point me to the right direction.
>
> merry christmas,
> - niel
> -
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Re: newbie

[Frank Kotler]

Niel A wrote:
> hello all!
> 
> i'm taking linux assembly as a hobby for christmas

... and for New Year you're doing micro-code? :)

> and i found your great site. the tutorials have been much helpful.
> 
> anyway, i meant to ask something.. 
> 
> section .data
> 	string: db "hi!",10
> 
> and i wanna capitalize the small letter 'h'.
> 
> at first i used
> 	mov di, string ; but di is 16 bits and ld complains

Right. As Fred explains, an address is 32 bits (or 64).

> so i eventually started using the 32 bit ones to do the capitalisation operation. but for some reason, i lose all other letters, including the linefeed.

Sounds like maybe you went too far. The address is 32 bits (or 64), but 
the characters of the string are only a byte (8 bits). If you tried to 
"uppercase" a whole 32 bits, you'd lose the whole thing, including the 
linefeed.

> please point me to the right direction.

Easy way:

sub byte [string], 32

maybe you'd write it as:

sub byte [string], 'a' - 'A'

to make it more "self-documenting". But a more flexible way, using some 
registers...

mov edi, string
mov al, [edi]
cmp al, 'a'  ; don't "uppercase" it unless
jb skip      ; it's lower case!
cmp al, 'z'
ja skip
sub al, 'a' - 'A'
mov [edi], al  ; store it back in "string"
skip:

...perhaps "inc edi", and loop back do do the next letter, or whatever...

inc edi
mov byte [edi], 'a'  ; change it to "Ha!"

Have fun.

> merry christmas,

Same to you and yours... and the rest of the list.

Best,
Frank

newbie

[Niel A]

hello all!

i'm taking linux assembly as a hobby for christmas and i found your great site. the tutorials have been much helpful.

anyway, i meant to ask something.. 

section .data
	string: db "hi!",10

and i wanna capitalize the small letter 'h'.

at first i used
	mov di, string ; but di is 16 bits and ld complains

so i eventually started using the 32 bit ones to do the capitalisation operation. but for some reason, i lose all other letters, including the linefeed.

please point me to the right direction.

merry christmas,
- niel

Re: newbie

[Niel A]

thanks for you help and clarifications!

my learning continues! looking forward to more posts....

again, merry christmas. and thank you.

tidings,
 - niel