How can I shuffle bits efficiently?

Question

I need to shuffle a 16 bit unsigned integer in a way that the even indexes land in the lower byte, and the odd indexes land in the upper byte.

input:
fedcba9         


        

Answer 1

You could use a 256-byte table for each byte of your 16-bit number, crafted so that your even/odd condition is satisfied. Hand-code the table entries (or use the algorithm you already have) to create the tables, and then the shuffling will be done at compile time. That would essentially be a translation table concept.