Extract a Bit Field from a 32-bit Register

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

uint32_t extract_field(uint32_t reg, uint8_t pos, uint8_t len) {
    
    
    return (reg>>pos) & ((1<<len)-1);

    
}

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;
}

reg>>pos : starts the integer  from the required bit. 

mask ((1>>len)-1) : This mask clears all the bits beyond the len value

for example if len == 3, then (1>>len) operation gives the value 00001000 and the subtrating '1' from 1000 will set the required first 3 bits and clear all other bits. 

Hence anding the two expressions gives the desired value.