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)
{
    uint32_t field = (((1 << len) - 1) << pos); // field of 1s you want to clear

    reg &= ~field; //clear that field

    reg |= ((val & ((1 << len) - 1)) << pos); //add the val in the field

    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;
}