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

This works and may be easier to understand, but bit manipulations are so cheap that I wouldn't worry much about efficiency.

#include 
#include 

void main() {
  unsigned int c = 0x1234, b;

  b = (c & 0xf000) * 0x11000 + (c & 0x0f00) * 0x01100 +
      (c & 0x00f0) * 0x00110 + (c & 0x000f) * 0x00011;

  printf("%x -> %x\n", c, b);
}