Is there a more efficient way of expanding a char to an uint64_t?

Question

I want to inflate an unsigned char to an uint64_t by repeating each bit 8 times. E.g.

char -> uint64_t
0x00 -> 0x00
0x01 ->         


        

Answer 1

If you're looking for efficiency use a lookup table: a static array of 256 entries, each already holding the required result. You can use your code above to generate it.