Sane

If I have in my allocated space, an arbitrary value, let's say:


How can I right shift, say, the third byte one over?

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DaWei

What you're showing isn't a byte, but a nybble (4 bits). Depending upon your processor, you may be able to shift a memory byte, or you may have to pull the associated bytes into registers and shift there. You'll have to respect the boundaries your uP gives you. All that said, you can shift bits between locations by shifting them through the carry flag, one bit at a time. In other words, shift the src one bit right, into the carry, shift the dest one bit right, either from the carry, or shift, then set the msb according to the carry. Wash, rinse, and repeat as necessary.

In right shifts you generally have the choice to have a zero shift in, or have the sign bit replicate itself, and sometimes to have the carry shift in. You'll have to check for your specific uP. Look for shift and/or rotate instructions.

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Sane

Whoops. I rushed my example too quickly.

So shifting has to be done manually? Start from the right and keep shifting one over until you're done? I was hoping there was something more efficient.

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DaWei

Well, you shift all the bits at once, just one position at a time. It isn't that inefficient. It's a binary divide by two. You could always just pick up the byte and sling it next door, then do whatever you want with its original home. If you want to work with things that don't conform to available boundaries, then you're going to get into masking and combining and all that hooraw.

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lectricpharaoh

If I understand you right, and assuming you're only wanting to work within the defined boundaries (byte, word, etc, depending on processor) you might look into whether there is a rotate instruction available.

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DaWei

:beard:

lectricpharaoh

My bad. That's what I get for not sleeping, eh?

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A man's knowledge is like an expanding sphere, the surface corresponding to the boundary between the known and the unknown. As the sphere grows, so does its surface; the more a man learns, the more he realizes how much he does not know. Hence, the most ignorant man thinks he knows it all. - L. Sprague de Camp