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) {
    // validate input

    // create mask for clearing bits
    uint32_t mask = 0; 
    if (len >= 32)
    {
        mask = 0xFFFFFFFF;
    }
    else
    {
        mask = ((1u << len) - 1);
    }

    // clear bits 
    reg &= ~(mask << pos);

    // set bits
    reg |= ((val & mask) <<  pos); 

    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;
}