AVR-Chat

Dave VanHorn wrote:

> Speed contest: 	 Fast code desired, space is no object.
> 
> Task: 			Make UP look like Down by rotating all the bits in a byte.
> 
> Input in TEMP, output in TEMP2 or for bonus points, in TEMP, such that
> 
> Input: 	7,6,5,4,3,2,1,0      10101110 or AE
> 
> Routine happens, then
> 
> Output: 0,1,2,3,4,5,6,7    01110101 or 75
> 
> The obvious solution is to clear the output and set the bits with 
> SBRC like this:
> 
> ;
> ;*************************************************************************************
> ;
> ;Bit swap end for end.
> ;
> Untwist:
> 	push	TEMP2			;
> 	clr	TEMP2			;
> 
> 	sbrc	TEMP,0		;
> 	sbr	TEMP2,1<<7		;
> 
> 	sbrc	TEMP,1		;
> 	sbr	TEMP2,1<<6		;
> 
> 	sbrc	TEMP,2		;
> 	sbr	TEMP2,1<<5		;
> 
> 	sbrc	TEMP,3		;
> 	sbr	TEMP2,1<<4		;
> 
> 	sbrc	TEMP,4		;
> 	sbr	TEMP2,1<<3		;
> 
> 	sbrc	TEMP,5		;
> 	sbr	TEMP2,1<<2		;
> 
> 	sbrc	TEMP,6		;
> 	sbr	TEMP2,1<<1		;
> 
> 	sbrc	TEMP,7		;
> 	sbr	TEMP2,1<<0		;
> 
> 	mov	TEMP,TEMP2		;
> 
> 	pop	TEMP2			
> 	ret				;
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
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> 

Solution 1

Cross wire port A to Port B (or any other port combination. Output byte 
on one port and read back on another.

Solution 2

Use a look up table and index the answer by the question byte. 256 bytes 
+ the load register with answer.

Don't think you can can quicker than these.