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;
    uint8_t count = 0;
    uint8_t num = pos;

    while (count < len) {
        mask = mask | (1 << num);
        num++;
        count++;
    }
    reg = reg & ~mask;
    val = val << pos;

    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;
}