Question

How to reverse all the bits in an integer in C

Answer 1

#include <stdio.h>

void print_bits(unsigned int n) { 
    for (int i = 31; i >= 0; i--)
       printf("%d", (n >> i) & 1);
    printf("\n");
}

unsigned int reverse_bits(unsigned int n) { 
    unsigned int total_bits = sizeof(n) * 8; 
    unsigned int reverse_n = 0; 
    
    for (int i = 0; i < total_bits; i++) { 
        if((n & (1 << i))) 
           reverse_n |= 1 << ((total_bits - 1) - i);   
   } 
    return reverse_n; 
} 


int main() {
    int n = 13;
   
    print_bits(n);
    
    n = reverse_bits(n);
    
    print_bits(n);

    return 0;
}



/*
run:

00000000000000000000000000001101
10110000000000000000000000000000

*/

 

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