Re: [Sub-sonic-development] Swapping Endians

[David O. <da...@ga...>]

On Fri, 30 Jun 2000, Dean Bilotti wrote:
> I've been playing with assembly speeding up my BSP compiler over the last 
> few days and I came accross a problem where I had to flip BCD bytes in a 
> register. This is similar to the Endian Swap you have to do for the mod's.
> 
> I basically had to Endian Swap 32-bit integers.
> 
> The way I saw it there were 2 viable methods for the 16 bit integer:
> 
> mov ax, Value	; 1 clock
> xor ah, al	; 1 clock
> xor al, ah	; 1 clock
> xor ah, al	; 1 clock
> 
> and
> 
> mov ax, Value	; 1 clock
> xchg ah, al	; 3 clocks

Hmm... Is rotation by 8 bits 3 clocks as well?

Anyway, have you considered what these clock counts are in real life,
with the pipeline and multiple ALUs in action?


//David


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