Replace Bit Field in a 32-bit Register

Code

#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 = 0;

    for (int i = 0; i < len; i++) {
        mask = (mask << 1) | 1;
    }

    val = val & mask;

    val <<= pos;
    mask <<= pos;

    return (reg & ~mask) | 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;
}

Solving Approach