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) {
    int i;
    uint32_t ex;
    for(i=0;i<len;i++){
        ex = val & (0x01<<i);
        if(ex) reg |= 0x01<<(pos+i);
        else reg = reg & (~(0x01<<pos+i));
    }
    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;
}