Extract a Bit Field from a 32-bit Register

Code

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

uint32_t extract_field(uint32_t reg, uint8_t pos, uint8_t len) {
    // Your code here
    uint32_t val = 0;
    uint32_t mask = ((1U << (len)) - 1) << pos;
    mask &= reg;
    return mask >> pos;
}

int main() {
    uint32_t reg;
    uint8_t pos, len;
    scanf("%u %hhu %hhu", &reg, &pos, &len);
    printf("%u", extract_field(reg, pos, len));
    return 0;
}

Solving Approach

So First I created a mask that creates all 1's by (1U << len) -1, 

So essentially, 1U << len creates a 1 followed by many zeros, and the -1 reduces it to all ones

for ex: the len = 3, then ((1U << 3) - 1) ==> 0b1000 - 1 ==> 0b111, which practically gives us the mask we need and AND it with the reg to get final value