18. Set Multiple Bits in 8-bit Register

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

uint8_t set_range(uint8_t reg, uint8_t start, uint8_t end) {
    uint8_t field_length = end - start + 1;
    uint8_t mask = 0x0;

    switch (field_length) {
        case 0:
            break;
        case 1:
            mask = 0x01;
            break;
        case 2:
            mask = 0x03;
            break;
        case 3:
            mask = 0x07;
            break;
        case 4:
            mask = 0x0F;
            break;
        case 5:
            mask = 0x1F;
            break;
        case 6:
            mask = 0x3F;
            break;
        case 7:
            mask = 0x7F;
            break;
        case 8:
            mask = 0xFF;
            break;
    }
    
    reg |= (mask << start); 
    return reg;
}

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