Testing if an integer is an uppercase ASCII letter using bit manipulation

Question

For an assignment, I\'m trying to make some code in C that uses only bit manipulation to test if an integer is an ASCII uppercase letter. The letter will be given by its ASCII c

Answer 1

... to see if a letter is uppercase

Simplification: Let us assume ranges [A-Z] and [a-z] char differ by the same value which is a power of 2. So 'B'-'b' equals 'X'-'x', etc.

#define CASE_MASK ('A' ^ 'a')

// Is letter uppercase?
int is_letter_upper(int ch) {
   return (ch & CASE_MASK) == ('A' & CASE_MASK);
}

// Is letter lowercase?
int is_letter_lower(int ch) {
   return (ch & CASE_MASK) == ('a' & CASE_MASK);
}

This works for ASCII and EBCIDIC

A more "bit manipulation" answer

int is_letter_upperBM(int ch) {
   return !((ch & CASE_MASK) ^ ('A' & CASE_MASK));
}