Question

How to extract N bits from start bit of a 32-bit unsigned integer in C

Answer 1

#include <stdio.h>
  
void print_bits(unsigned int n, int size) {
    for (unsigned int i = 1 << (size - 1); i > 0; i = i / 2) {
        (n & i) ? printf("1") : printf("0");
    }
}
 
int get_last_N_bits_from_start_bit(unsigned int number, int N, int startBit) {
    unsigned int mask = ((1 << N) - 1) << startBit;
    
    return number & mask;
}
 
int main()
{
    unsigned int number = 441; // 0000000-11011-1001
    int N = 5;
     
    print_bits(number, 16);
    printf("\n");
     
    int lastNbits = get_last_N_bits_from_start_bit(number, N, 4);
     
    print_bits(lastNbits, 16);
 
    return 0;
}
  
  
  
    
/*
run:
    
0000000110111001
0000000110110000
    
*/

 

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