Question

I need to take all the digits in a hex number and “invert” them: all zeroes become non-zeroes (F) and all non-zeroes become zeroes.

I tried:

void someFunction(DWORD hexVal)
{
     //...
     hexVal = ~hexVal;
     //...
}

and this changed 0xE0000000 to 0x1FFFFFFF instead of 0x0FFFFFFF.

How can I produce the desired result?

Answer 1

This should give you the desired result for 2 bytes. You get the idea for 4 bytes.

hexval = ((hexval & 0xf000) ? 0 : 0xf000) |
         ((hexval & 0xf00) ? 0 : 0xf00) |
         ((hexval & 0xf0) ? 0 : 0xf0) |
         ((hexval & 0xf) ? 0 : 0xf);