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) {
    // Your code here
uint32_t mask = ~0U; // all ones
mask <<= len; // inserted zeros from beggining to len 
mask = ~mask; // negate now we have 1s from beginning to len
mask <<= pos; // move the 1s pos times so we get on the alligned target area all ones rest zeros

val <<= pos; // allign val with reg

reg = (reg & ~mask) | val; // make reg as it is except in target area it becomes zeros since we negated mask first then or it with val to change this area

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;
}