Convert 0x1234 to 0x11223344

Question

How do I expand the hexadecimal number 0x1234 to 0x11223344 in a high-performance way?

unsigned int c = 0x1234, b;
b = (c & 0xff) << 4 | c & 0xf |          


        

Answer 1

Assuming that, you want to always convert 0xWXYZ to 0xWWXXYYZZ, I believe that below solution would be little faster than the one you suggested:

unsigned int c = 0x1234;     
unsigned int b = (c & 0xf) | ((c & 0xf0) << 4) |
                 ((c & 0xf00) << 8) | ((c & 0xf000) << 12);
b |= (b << 4);

Notice that, one &(and) operation is saved from your solution. :-)
Demo.