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Index > DOS > Uppercasing characters

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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
I was trying to find a way to convert lower cased characters to upper cased character, when I found a tutorial on ASCII characters. Then, I conjured up the code below.

What the upcase function does is, it takes a character and checks its range, which is between 60h - 7Bh. (The character _is_ a common letter).
If the character falls between that range, it is AND by 11011111b.
The 1 bits will return the original values but, the 0 at bit 5 will toggle that bit to 0 which will set it as a upper cased character.
Code:
   org 100h

   macro pause
   {
         push  ax
         xor   ax,ax
         int   16h
         pop   ax
   }

   jmp start

   message db "hello world!",0

   start:
         mov   si,message
         call  upcase          ; convert to uppercased
         inc   si              ; clear last value in SI
         mov   si,message
         call  pstr            ; go print string
         pause                 ; pause to view result
         int 20h               ; exit program




;===========================================
; FUNCTIONS
;-------------------------------------------
;  Converts lower cased character into upper
;  cased.
;-------------------------------------------
   upcase:
   ;in:  si = string

         push  ax
         xor   ax,ax           ; clear AX
      .loop:
         mov   al,[si]         ; load byte from SI
         cmp   al,60h          ; is byte < 'a'
         jbe   @f              ; then, go get next byte
         cmp   al,7Bh          ; is byte > 'z'
         jae   @f              ; then, go get next byte
                               ; Only bytes in the range of 'a' - 'z are converted.

         and   al,11011111b    ; toggle bit 5 to 0
       @@:
         mov   [si],al         ; update character stored in data, with uppercased character
         inc   si              ; step forward to next character
         or    al,al           ; is this the end of the string?
         jz   .done            ; if so, then return.
         jmp  .loop            ; else, go convert next character

      .done:
         pop   ax
         ret

;-------------------------------------------
;  Prints string
;-------------------------------------------
   pstr:
   ;in:  si = string
      .loop:
         lodsb
         or    al,al
         jz   .done
         mov   ah,0Eh
         int   10h
         jmp  .loop

      .done:
         ret    

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meshnix
Post 26 Jun 2010, 00:46
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bitshifter



Joined: 04 Dec 2007
Posts: 764
Location: Massachusetts, USA
bitshifter
This is not the best but is very simple Razz
Code:
toupper: ; DS:SI -> ASCIIZ string
        lodsb
        test    al,al
        jz      .finished
        cmp     al,'a'
        jb      toupper
        cmp     al,'z'
        ja      toupper
        sub     al,32
        dec     si
        mov     byte[ds:si],al
        inc     si
        jmp     toupper
  .finished:
        ret      

_________________
Coding a 3D game engine with fasm is like trying to eat an elephant,
you just have to keep focused and take it one 'byte' at a time.
Post 26 Jun 2010, 01:04
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
Lets simplify it further Razz
Code:
toupper: ; DS:SI -> ASCIIZ string
        lodsb
        test    al,al
        jz      .finished

        sub     al,'a'           ; --+
        cmp     al,'z'-'a'       ;   |
        ja      toupper          ;   |
                                 ;   |
        sub     al, 'a'-'A' - 'a'; <-+
        mov     [si-1],al
        jmp     toupper

  .finished:
        ret    
Post 26 Jun 2010, 01:36
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b1528932



Joined: 21 May 2010
Posts: 287
b1528932
character upper/lower case isnt something you can convert to.

you need a character map wich include entries for characters containing lowercase and uppercase version (and field indicating presence of both of them, one, or none). Another thing is encoding, charc can be stored as ansi, utf16, utf8 or other methods. this require not only a map, but an api.
Post 26 Jun 2010, 11:46
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17474
Location: In your JS exploiting you and your system
revolution
b1528932: This is the DOS forum. So things like UTF8, ANSI etc. are pretty much ruled out for most programs. I think it is safe to assume that ASCII will be the character set used in 99.99% of cases.
Post 26 Jun 2010, 12:23
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
bitshifter, it is quite simpler than mine -- easier to understand too.

LocoDelAssembly,
Code:
...
sub al, 'a'='A' - 'a'
...    
Nice, but it computes to -65. Does the compiler treat signed integers as unsigned integers, or does it just wrap around?

b1528932, when I said convert I didn't mean converting ASCII to Unicode.
Post 26 Jun 2010, 12:54
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17474
Location: In your JS exploiting you and your system
revolution
MeshNix wrote:
... it computes to -65. Does the compiler treat signed integers as unsigned integers, or does it just wrap around?
Values from -128 to +255 are valid for 8-bit types.

As you might expect, -1==255, ... ,-128==+128.
Post 26 Jun 2010, 12:59
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
This would mean that -65==191, doesn't it?
Post 26 Jun 2010, 13:16
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17474
Location: In your JS exploiting you and your system
revolution
MeshNix wrote:
This would mean that -65==191, doesn't it?
Yes
Post 26 Jun 2010, 13:19
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Picnic



Joined: 05 May 2007
Posts: 1288
Location: behind the arc
Picnic
this should also work, although raises LocoDelAssembly's code to 21 bytes.

Code:
.if ( al > 60h & al < 7bh )
 xor al, 20h       ; toggle case
.endif
    
Post 26 Jun 2010, 13:32
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
revolution, how does this actually work? -65 was treated as if it was unsigned. Does signed or unsigned matter in ASCII?



Picnic wrote:
this should also work, although raises LocoDelAssembly's code to 21 bytes.
Code:
.if ( al > 60h & al < 7bh ) 
        xor al, 20h       ; toggle case 
.endif 
    

Actually it would make the character lowercased.
Try:
Code:
.if ( al > 40h & al < 5Bh )
        xor al, 20h       ; toggle case
.endif    

Great! Now I now how to do reverse uppercasing.
Post 26 Jun 2010, 17:00
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17474
Location: In your JS exploiting you and your system
revolution
The CPU doesn't know or care about signed/unsigned, it is all just binary. Only the programmers will know about signs when testing the flags.
Post 26 Jun 2010, 17:28
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
Oh, I see; it's up to the programmer.
Post 26 Jun 2010, 18:02
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edfed



Joined: 20 Feb 2006
Posts: 4240
Location: 2018
edfed
maybe just a 256 bytes look up table can be really enough and better.
for example, to change the case of éàèêîëï, all these chars are in ascii, depending on the charset used of course.
Post 26 Jun 2010, 21:00
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DOS386



Joined: 08 Dec 2006
Posts: 1901
DOS386
> http://board.flatassembler.net/topic.php?t=9736 search for "SSUPPER"

> to change the case of éàèêîëï, all these chars are in ascii, depending on the charset used of course.

Where ??? This never worked AFAIK Laughing
Post 27 Jun 2010, 11:26
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rugxulo



Joined: 09 Aug 2005
Posts: 2341
Location: Usono (aka, USA)
rugxulo
revolution wrote:
b1528932: This is the DOS forum. So things like UTF8, ANSI etc. are pretty much ruled out for most programs. I think it is safe to assume that ASCII will be the character set used in 99.99% of cases.


It seems Europeans are more conscientious of this than others. And, IIRC, even Tomasz uses this (int 21h, 652xh) in FASMD:

http://www.delorie.com/djgpp/doc/rbinter/id/77/31.html

P.S. I always just used "and dl,0DFh" to uppercase. Toggle is "xor dl, 20h". And, unless I'm remembering wrong, "or dl, 20h" will lowercase.
Post 28 Jun 2010, 06:36
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