Replace Bit Field in a 32-bit Register

Code

#include <stdio.h>
#include <stdint.h>
#include <math.h>

uint32_t replace_field(uint32_t reg, uint32_t val, uint8_t pos, uint8_t len) 
{
    uint32_t shift_num = pow(2 , len) - 1;

    shift_num = shift_num << pos;

    reg = reg & ~(shift_num);

    val = val << pos;

    reg = reg | val;

    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;
}

Solving Approach