21. Replace Bit Field in a 32-bit Register

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

uint8_t createMask(uint8_t len) {
    uint8_t mask = 0;

    len--;
    while(len) {
        mask |= (1 << len);
        len--;

        if (len == 0) 
            mask |= (1 << len);
    }

    return mask;
}

uint32_t replace_field(uint32_t reg, uint32_t val, uint8_t pos, uint8_t len) {
    // Your code here
    uint8_t mask = createMask(len);
    reg &= ~(mask << pos);
    reg |= (val & mask) << pos;
    return reg;
}

int main() {
    uint32_t reg, val;
    uint8_t pos, len;
    scanf("%u %u %hhu %hhu", &reg, &val, &pos, &len);
    printf("%u", replace_field(reg, val, pos, len));
    return 0;
}