How do x86 sub-register specific assembly instructions interact with the whole? : <p>Mostly asking about arithmetic operations.</p>

<p>Example: </p>

<p>Assume 32-bit hardware
eax stores 0xff000000</p>

<p>If "sub al, 0x10" is called, do the higher bytes/bits change?
Does it affect the whole register, or does it confine the operation to that subdivision?</p>

<p>Do other operations (add, sal, sar, etc.) have consistent whole/sub register interactions?</p>
