18. Set Multiple Bits in 8-bit Register

#include <stdint.h>
#include <stdio.h>

uint8_t set_range(uint8_t reg, uint8_t start, uint8_t end) {
  uint8_t upper_bound = end - start + 1;
  uint8_t ones = (1 << upper_bound) - 1;
  uint8_t mask = ones << start;

  return reg | mask;
}

int main() {
  uint8_t reg, start, end;
  scanf("%hhu %hhu %hhu", &reg, &start, &end);
  printf("%u", set_range(reg, start, end));
  return 0;
}