bug702.cpp

1     #include <stdio.h>
2
3     int no_of_bits( int n )
4          {
5         int count = 0;
6         while( n )
7             {
8             if( n & 1 ) ++count;
9             n >>= 1;
10            }
11        return count;
12        }
13
14    void test( int n )
15        {
16        printf( "there are %d 1's in 0x%x\n", no_of_bits(n), n );
17        }
18
19    int main()
20        {  test( 0xFFFFFFFF ); return 0; }

This program seems to be taking an inordinate amount of time. In fact it's still running :-}. What's the problem?

bug702.cpp lint Output

--- Module:   bug702.cpp
               _
        n >>= 1;
bug702.cpp(9) : Info 702: Shift right of signed quantity (int)
                     _
    test( 0xFFFFFFFF );
bug702.cpp(20) : Warning 569: Loss of information (arg. no. 1)
    (32 bits to 31 bits)

Reference Manual Explanation

 
702   Shift right of signed quantity (int)  -- Shifts are
      normally accomplished on unsigned operands.  Shifting an
      int right is machine dependent (sign fill vs. zero fill).