21. Replace Bit Field in a 32-bit Register

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

uint32_t replace_field(uint32_t reg, uint32_t val, uint8_t pos, uint8_t len) {
    // Your code here
    const uint16_t end_bit = (uint16_t)pos + (uint16_t)len;

    if((len == 0U) || (end_bit > 32U)){
        return reg;
    }

    uint64_t mask = (uint64_t)((1ULL << len) - 1ULL);

    reg &= ~((uint32_t)mask << pos);
    reg |= (uint32_t)((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;
}