Is a logical right shift by a power of 2 faster in AVR?

Question

I would like to know if performing a logical right shift is faster when shifting by a power of 2

For example, is

myUnsigned >> 4

Answer 1

Let's look at the datasheet:

http://atmel.com/dyn/resources/prod_documents/8271S.pdf

As far as I can see, the ASR (arithmetic shift right) always shifts by one bit and cannot take the number of bits to shift; it takes one cycle to execute. Therefore, shifting right by n bits will take n cycles. Powers of two behave just the same as any other number.

Answer 2

If your targer processor has a bit-shift instruction (which is very likely), then it depends on the hardware-implementation of that instruction if there will be any difference between shifting a power-of-2 bits, or shifting some other number. However, it is unlikely to make a difference.

Answer 3

Disassemble first then time the code. Dont be discouraged by people telling you, you are wasting your time. The knowledge you gain will put you in a position to be the goto person for putting out the big company fires. The number of people with real behind the curtain knowledge is dropping at an alarming rate in this industry.

Sounds like others explained the real answer here, which disassembly would have shown, single bit shift instruction. So 4 shifts will take 133% of the time that 3 shifts took, or 3 shifts is 75% of the time of 4 shifts depending on how you compared the numbers. And your measurements should reflect that difference, if they dont I would continue with this experiment until you completely understand the execution times.