AVR-Chat

On 18 Jun 2004 at 22:47, David VanHorn wrote:

> 
> What's the fastest way to get the exclusive or, of four bits in a register?
> 
> 0000 = 0
> 0001 = 1
> 0010 = 1
> 0011 = 0
> 0100 = 1
> 0101 = 0
> 0110 = 0
> 0111 = 0
>  and so on...
> 
> Not for a parity generator, but I think it ends up as the same problem.
> 
	
	clr		sum
	sbrc		tmp,0
	inc		sum
	sbrc		tmp,1
	inc		sum
	sbrc		tmp,2
	inc		sum
	sbrc		tmp,3
	inc		sum

	Another way:

	clr		sum
	lsr		tmp
	adc		sum, tmp
	lsr		tmp
	lsr		tmp
	adc		sum, tmp

	The XOR of the four 'tmp' bits is in 'sum', bit 0.

	HTH.
	Mark Jordan