How to count set bits in a floating point number in C?
Given a floating point number, write a function to count set bits in its binary representation.
For example, floating point representation of 0.15625 has 6 set bits (See this). A typical C compiler uses single precision floating point format.
We can use the idea discussed here. The idea is to take address of the given floating point number in a pointer variable, typecast the pointer to char * type and process individual bytes one by one. We can easily count set bits in a char using the techniques discussed here.
Following is C implementation of the above idea.
C
#include <stdio.h> // A utility function to count set bits in a char. // Refer http://goo.gl/eHF6Y8 for details of this function. unsigned int countSetBitsChar( char n) { unsigned int count = 0; while (n) { n &= (n-1); count++; } return count; } // Returns set bits in binary representation of x unsigned int countSetBitsFloat( float x) { // Count number of chars (or bytes) in binary representation of float unsigned int n = sizeof ( float )/ sizeof ( char ); // typecast address of x to a char pointer char *ptr = ( char *)&x; int count = 0; // To store the result for ( int i = 0; i < n; i++) { count += countSetBitsChar(*ptr); ptr++; } return count; } // Driver program to test above function int main() { float x = 0.15625; printf ( "Binary representation of %f has %u set bits " , x, countSetBitsFloat(x)); return 0; } |
Output:
Binary representation of 0.156250 has 6 set bits
Time Complexity: O(nlogn)
Auxiliary Space: O(1)