18. Set Multiple Bits in 8-bit Register

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

#define SET_REG_BIT(reg, pos) ((reg) |= (1 << (pos)))

uint8_t set_range(uint8_t reg, uint8_t start, uint8_t end) {
    uint8_t total_bits = (end-start) + 1; // Figure out total number of bits to set
    uint8_t mask = ((1 << total_bits) - 1) << 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;
}