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) {
    
    uint32_t mask = ((1U<<len)-1);
    reg &= ~(mask<<pos);

    reg |= val<<pos;

    // int j = 0;
    // for(int i = pos; i<pos+len; i++){

    //     reg &= ~(1<<i);
    //     reg |= ((val&(1<<j))>>j)<<i;

    //     j++;
    // }

    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;
}