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

Here's another attempt, using eight operations:

b = (((c & 0x0F0F) * 0x0101) & 0x00F000F) + 
    (((c & 0xF0F0) * 0x1010) & 0xF000F00);
b += b * 0x10;

printf("%x\n",b); //Shows '0x11223344'

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*Note, this post originally contained quite different code, based on Interleave bits by Binary Magic Numbers from Sean Anderson's bithacks page. But that wasn't quite what the OP was asking. so it has ben removed. The majority of the comments below refer to that missing version.