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) {
    // Step 1: Create a mask for the target field
    uint32_t mask = ((1U << len) - 1) << pos;

    // Step 2: Clear the target bits in reg
    reg &= ~mask;

    // Step 3: Align val to the correct position and mask it
    val = (val & ((1U << len) - 1)) << pos;

    // Step 4: Combine reg and val
    return reg | val;
}

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;
}