M5-0-20 clarification

[rt1980]

Hi All,

Rule 5-0-20 states that "Non-constant operands to a binary bitwise operator shall have the same underlying type." seems to make sense but my colleagues and I are bit unsure why the non-constant qualifier? 

Consider the following example. It's not clear to us why the first should be allowed if the second is not.

Code:

int foo(int i) {
  const unsigned char mask = ~(0x10);
  return i ^ mask; // compliant: mask is const
}

int foo(int i) {
  unsigned char mask = ~(0x10);
  return i ^ mask; // non-compliant: mask is not const and a different type than i
}

Thanks for your help!
Rafe