Representing only a set of bits in a binary number

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Is there any way to exit an if statement without using a loop in VHDL

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No. If you are trying to do this, then you have a misunderstanding of VHDL (and other programming langauges)

The if statements are meant to represent decisions at a given moment in time. why would you exit an if statement?

Your code would also no work on real hardware. I highly suggest going back to your text book and tutorials on digital logic design.