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
    if(len==0 || (len+pos)>32) return reg;
    uint32_t mask=((1u<<len)-1)<<pos;
    reg &= ~mask;
    reg|=(val<<pos)&mask;
    return reg;
    //Input: reg = 0b1111 1111, val = 0b0000, pos = 4, len = 4  
    //Output: 0b0000 1111
}

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;
}