Replace Bit Field in a 32-bit Register

Code

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

#define MASK(pos, len) (((1u<<len)-1)<<pos) 

uint32_t replace_field(uint32_t reg, uint32_t val, uint8_t pos, uint8_t len) 
{ 
    reg &= ~MASK(pos, len); 
    reg |= ((val & ((1u<<len)-1)) << pos); 
    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