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) {
    /*
    len = 4
    10000 -> 01111  
    pos = 4 
    -> mask = 01110000
    ~mask = 10001111
    */
    uint32_t mask = ((1<<len)-1) << pos;
    reg &= ~mask;
    reg |= (val<<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;
}