Convert an 8 bit data to 3 bit data

PROGRAMMING LANGUAGE: C

I've a 8 bit data with only 3 bit used, for example:

0110 0001

Where 0 indicate unused bit that are always set to 0 and 1 indicate bits that change.

I want to convert this 0110 0001 8 bit to 3 bit that indicate this 3 used bits.

For example

0110 0001 --> 111

0010 0001 --> 011

0000 0000 --> 000

0100 0001 --> 101

How I can do that with minimal operations?