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) {
    if (len == 0) return reg;

    uint32_t mask_low = (len >= 32) ? 0xFFFFFFFFu : ((1u << len) - 1u);
    uint32_t field_mask = mask_low << pos;

    uint32_t reg_cleared = reg & ~field_mask;
    uint32_t inserted = (val & mask_low) << pos;

    return reg_cleared | inserted;
}

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;
}