Question

How to get the highest power of 2 that is less than or equal to N in C

Answer 1

#include <stdio.h>

int highest_power_of_2_less_or_equal_to_n(int n) { 
    int power = 0; 
    for (int i = n; i >= 1; i--) { 
        // i == power of 2 ?
        if ((i & (i - 1)) == 0) { // 10 (1010) 9 (1001) 8 (1000) 7 (0111)
            power = i; 
            break; 
        } 
    } 
    return power; 
} 
   
int main() 
{ 
    int n = 17;
    printf("%i\n", highest_power_of_2_less_or_equal_to_n(n)); 
     
    n = 10;
    printf("%i\n", highest_power_of_2_less_or_equal_to_n(n)); 
     
    n = 64;
    printf("%i\n", highest_power_of_2_less_or_equal_to_n(n)); 
     
    return 0; 
}


 
/*
run:
 
16
8
64
 
*/

 

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