Byte to hex, once again.

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Fanael

Joined: 03 Jul 2009
Posts: 168

Fanael 15 Aug 2010, 19:13

Yet another little challenge for you all: write a code (smaller = better) that converts a byte in AL to hexadecimal.

Rules:
* The code has to compile fine with use32 and use64,
* No branches,
* The same goes for conditional moves,
* No memory accesses, except writing the result somewhere.

15 Aug 2010, 19:13

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 15 Aug 2010, 19:42

to hexadecimal what? two ascii chars in AX? in memory? zero terminated? Or whatever goes?

15 Aug 2010, 19:42

Fanael

Joined: 03 Jul 2009
Posts: 168

Fanael 15 Aug 2010, 19:52

vid wrote:

Or whatever goes?

Yeah, as long as characters are encoded as ASCII.

15 Aug 2010, 19:52

chaoscode

Joined: 21 Nov 2006
Posts: 64

chaoscode 15 Aug 2010, 20:25

Code:

mov ah,al
shr ah,4
and ax,0x0F0F
rol ax,8
mov ebx,msg
xlatb
rol ax,8
xlatb

msg db "0123456789ABCDEF"

edit: added code tags

Last edited by chaoscode on 15 Aug 2010, 22:28; edited 1 time in total

15 Aug 2010, 20:25

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 15 Aug 2010, 20:45

chaoscode, you're violating the last rule.

15 Aug 2010, 20:45

chaoscode

Joined: 21 Nov 2006
Posts: 64

chaoscode 15 Aug 2010, 20:54

Code:

mov     ah,al
shr     ah,4
and     ax,0x0F0F
add     ax,0x3030
cmp     al,0x39
jna     @f
add     al,7
@@:
cmp     ah,0x39
jna     @f
add     ah,7
@@.

EDIT. added quote tags

Last edited by chaoscode on 15 Aug 2010, 22:29; edited 1 time in total

15 Aug 2010, 20:54

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 15 Aug 2010, 21:06

Now you violated the 2nd rule Laughing

15 Aug 2010, 21:06

chaoscode

Joined: 21 Nov 2006
Posts: 64

chaoscode 15 Aug 2010, 22:02

hmpf... it's quite difficult^^

15 Aug 2010, 22:02

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 15 Aug 2010, 22:14

I presume external functions are not allowed either Wink

chaoscode: please use [code] tags around your code.

15 Aug 2010, 22:14

Fanael

Joined: 03 Jul 2009
Posts: 168

Fanael 15 Aug 2010, 23:49

vid wrote:

I presume external functions are not allowed either

If you can call them without branching and touching memory, then they're of course allowed Wink

chaoscode wrote:

hmpf... it's quite difficult^^

Sure, it is difficult, but it's possible nevertheless Smile

15 Aug 2010, 23:49

mindcooler

Joined: 01 Dec 2009
Posts: 423
Location: Västerås, Sweden

mindcooler 15 Aug 2010, 23:55

Based on Revolution's. Violates #1.

AL -> AX

Code:

        mov     ah,al
        shr     al,4
        cmp     al,10
        sbb     al,069h
        das
        xchg    ah,al
        and     al,$0f
        cmp     al,10
        sbb     al,069h
        das

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15 Aug 2010, 23:55

chaoscode

Joined: 21 Nov 2006
Posts: 64

chaoscode 16 Aug 2010, 00:03

Code:

use64
format elf64 executable
entry start

start:
mov     eax,0
@@:
cmp eax,0
mov ax,0xE5
call func
mov ax,0x9A
call func
ret

func:
mov    ah,al
shr    ah,4
and     ax,0x0F0F
mov        dx,ax
xor    bx,bx
add    dl,0xF6
rcl  bl,1
ror     bl,1
sar     bl,7
and     bl,0x07
add  al,bl

add        dh,0xF6
rcl  bh,1
ror     bh,1
sar     bh,7
and     bh,0x07
add  ah,bh
add    ax,0x3030
ret

16 Aug 2010, 00:03

Alphonso

Joined: 16 Jan 2007
Posts: 295

Alphonso 16 Aug 2010, 05:31

Code:

         xor    ah,ah                  ; can we assume ah=0 ?
         mov    dx,ax                  ; could push but the stack is technically a memory op, isn't it?
         mov    bx,3030h               ; ascii offset
         mov    cx,110ah               ; ch=17, cl=10
         shr    al,4                   ; upper hex
         div    cl                     ; result = 0 for 0 to 9, 1 for A to F
         add    bh,ah                  ; add remainder to result BX, 0 to 9 = 0 to 9, A to F = 0 to 5
         mul    ch                     ; for 0 to 9 = 0, for A to F add +17 ascii offset
         add    bh,al                  ; add to result
         mov    ax,dx                  ; this could have been a pop if memory op allowed
         and    al,0fh                 ; lower hex
         div    cl                     ; as above
         add    bl,ah                  ;
         mul    ch                     ;
         add    bl,al                  ; BX = hex ascii of AL

Not very small, 33 Bytes for 16 and 37 Bytes for 32/64.

16 Aug 2010, 05:31

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 16 Aug 2010, 05:58

OK, big people is also getting in so I think it is OK to publish a spoiler Razz

Code:

ror ax, 4
and al, $0F
shr ah, 4
mov dh, 9

irps nibble, al ah
{
        cmp dh, nibble
        sbb dl, dl
        and dl, 'A' - '9' - 1
        add nibble, dl
}

add ax, '00'

(But probably could be further optimized)

This one is 33 bytes in both 32- and 64-bit.

AH holds least significant nibble intentionally.

16 Aug 2010, 05:58

Tyler

Joined: 19 Nov 2009
Posts: 1216
Location: NC, USA

Tyler 16 Aug 2010, 06:02

Code:

xor al,al
mov byte[buf], 0
mov byte[buf+1],0

buf rb 2

How's that? Laughing

16 Aug 2010, 06:02

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 16 Aug 2010, 09:04

Tyler wrote:

Code:

xor al,al
mov byte[buf], 0
mov byte[buf+1],0

buf rb 2

How's that? Laughing

That's wrong. It ought to be mov byte [...], '0'. But otherwise - good solution!

16 Aug 2010, 09:04

Fanael

Joined: 03 Jul 2009
Posts: 168

Fanael 16 Aug 2010, 09:36

Hehe, it could be optimized further:

Code:

xor al,al 
mov word [buf], '00' 

buf rb 2

But it fails (i.e. returns the wrong result) if AL is not equal to 0 Razz

chaoscode: accepted, 49 bytes.
Alphonso: accepted.
LocoDelAssembly: accepted.

16 Aug 2010, 09:36

Alphonso

Joined: 16 Jan 2007
Posts: 295

Alphonso 16 Aug 2010, 12:51

Well i suppose I could get rid of that horrible div.

Code:

         mov    ah,al
         shr    ah,4            ; use 'shr al,4' and
         and    al,0fh          ; 'and ah,0fh' to output Loco nibbles :p
         mov    ebx,eax
         xor    ecx,ecx
         mov    cl,7
         mul    ecx
         and    eax,4040h
         shr    eax,6
         mul    ecx
         add    ax,3030h
         add    ebx,eax         ; BX = hex ascii of AL or use 'add eax,ebx' for AX = hex ascii of AL.

31 Bytes for 32/64.

16 Aug 2010, 12:51

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 16 Aug 2010, 15:16

OK, if storing the value reversed is OK (Intel CPUs are little endian), then my entry could be this:

Code:

mov ah, al
and al, $0F
shr ah, 4
mov dh, 9

irps nibble, al ah
{
        cmp dh, nibble
        sbb dl, dl
        and dl, 'A' - '9' - 1
        add nibble, dl
}

add ax, '00'

Same size as Alphonso's code above.

16 Aug 2010, 15:16

Picnic

Joined: 05 May 2007
Posts: 1404
Location: Piraeus, Greece

Picnic 16 Aug 2010, 20:46

28 bytes for 32/64. Routine must be called.

Code:

Byte2Hex:
            mov ah, al
            shr al, 4
            mov dh, 9
            call @F
            xchg al, ah
            and al, 0Fh
    @@:     cmp dh, al
            sbb dl, dl
            and dl, 7
            add al, dl
            add al, '0'
            ret

16 Aug 2010, 20:46

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