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) 
{
    uint32_t S_val =0x00;
    uint32_t mask = 0x00;
    mask = (1 << len)-1;
    mask = mask << pos;
    reg = reg & ~mask;
    S_val = val << pos;
    reg = reg | S_val;
    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;
}

Solving Approach