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 i = pos;
    val = val << pos;
    while(len!=0)
    {
        reg = reg &~(1<<i);
        i++;
        len--;
    }
    reg = reg | 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;
}

move the value to the position wheer we want to replace
make the same position in the register to zeros

then just do the OR operation