if-elseif Statement: Most common conditions shall be handled first

·         Discuss the overhead of branching and why the most common case should be tested first in the (if – else) if construct to speed up execution.

o   Modern processors use pipelining.

From Wikipedia

o   This means that multiple commands are served in parallel

o   Ex:  in clock cycle 4

§  Cmd1: Fetch from memory

§  Cmd 2: Decode to the ALU

§  Cmd 3: Execute

§  Cmd 4: Write the result to the register or the memory

o   Complete example: http://en.wikipedia.org/wiki/Instruction_pipeline#Illustrated_example

o   This requires that the CPU know the next commands to execute

o   If we have conditional branches, then, the CPU will not be able to know the next commands, and then it will not be able to utilize the pipelining.

o   Hence, it is recommended that the most common condition be the first condition in if-else statement, so we do not have a lot of conditional branching.