Replace Bit Field in a 32-bit Register

Code

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

uint32_t replace_field(uint32_t reg, uint32_t val, uint8_t pos, uint8_t len) {
    //return val;
    int mask = 1<<pos;
    // int mask_val = 1;
    for(int i=1;i<len;i++){
        mask |= mask<<1;
        // mask_val |= mask_val<<1;
    }
    // return mask;
    val = val << pos;
    // return val;
    reg = reg & (~(mask));
    // return reg;
    return reg | val;
}

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;
}

Solving Approach