C - How to check if 8 bits are in 32 bit?

Question

I want to check if the 8 bits in a char are a substring of the 32 bits of an int.

a = 0110 1010 1011 0100 0000 0110 1010 0010 (32 bit int)
b = 0100 0000 (8 bit char)

is_in(a, b) --> true

Here is my code:

    for (int i = 0; i < 25; i++) {
       int tmp = a;
       tmp <<= 24;
       tmp >>= 24;
       int res = b ^ tmp;
       res <<= 24;
       res >>= 24;
       if (res == 0)
          return 1;
       else
          a >>= 1;
    }
    return 0;

I want it more efficient. Any idea?

Answer 1

Well, you could try...

bool is_in(uint32_t a, uint8_t b) {
  while (a >= b) {
    if ((a & 0xff) == b) return true;
    a >>= 1;
  }
  return false;
}