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bits swap 0<->2
hii
i want to swap the 1st bit with the 3rd

like
123
321
only in bits


this what i have in mind 



shr ecx, 1 

rcl eax, 1 

shr ecx, 1 

rcl eax, 1 

shr ecx, 1 

rcl eax, 1


instead of shr can be use bt this wont destory the 2nd register
another one 





	test ah,4

	jz @F

	test ah,1

	jnz _changed

	xor ah,4 or 1

	jmp _changed

	@@:

	test ah,1

	jz _changed

	xor ah,4 or 1

	_changed:




                mov dl,ah

	

         and ah,1 or 4

	xor ah,1 or 4

	jz _nochanged

	xor dl,1 or 4

_noneed:


EDIT:

found another one in the board 

	

mov  esi, 01110011010100010110001001000000b 

shl ecx, 2 

shr  esi, ecx 

and esi, 111b

any more ways ? ideas?
bye
thanks
eko
Posted on 2004-11-01 07:37:43 by eko
bits swap 0<->2
Nexo, posted a three instruction bit exchange here:
http://www.asmcommunity.net/board/viewtopic.php?t=6990&highlight=exchange

Here is code for specific case requested:
    test eax, 101y

    jnp @F

    xor eax, 101y

@@:
In English it would be stated: reverse bits when not the same.


BIT0 <= BIT0 xor (BIT0 xor BIT2)
BIT2 <= BIT2 xor (BIT0 xor BIT2)

...just like the register swap trick. :)
Posted on 2004-11-01 09:35:15 by bitRAKE