cbytebit-manipulationbitnibble

Hex of most significant nibble

I am having trouble with bitwise manipulation.

To do: The hex value of the most significant nibble of x equals y (assume 0 <= y <= 15)

Restrictions: may not use equality (==) or inequality (!=) tests, relative comparison operators, division, modulus, and multiplication, conditionals.

Problem: I need to make my function so that when msb = y it returns 1 and if it is not true 0. However, I keep getting zero even when i run it with 0xff. If someone could point me in the right direction that would be great. Thank you.

int sig_nib(int x, int y){

int shifright = x  >> 27;
int result = shifright & y;

return (result ^ y);
}
Solution

  • Silly restrictions. Who broke your compiler?

    Something like this should do it:

    bool sig_nib(int x, int y)
{
  const int top4 = (x >> 28) & 0xf;
  return !(top4 ^ y);
}

    It uses Boolean inversion (!) to re-interpret the integer result from the bitwise-xor.