21. Replace Bit Field in a 32-bit Register

#include <stdio.h>
#include <stdint.h>
    int mark;
    int xoa;
uint32_t replace_field(uint32_t reg, uint32_t val, uint8_t pos, uint8_t len) {
      mark = (val << (31 - len)) >> (31 - len);
      xoa = (1<<len)-1;
      reg &= ~(xoa << pos );
      reg |= (mark << 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;
}