18. Set Multiple Bits in 8-bit Register

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

uint8_t set_range(uint8_t reg, uint8_t start, uint8_t end) 
{
    uint8_t shift_num = pow( 2 , ( (end - start) + 1 ) ) - 1;

    return ( reg | (shift_num << start) );
}

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