Finding number of bits set in a given number

[BadKarma]

This works also, and its pretty fast ;P

  int A = 0xAA000000;
  int B;
  __asm
  {
    mov eax, dword ptr [A] ;
    mov ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    SHL eax,1 ;
    ADC ebx,0 ;
    MOV dword ptr [B],ebx ;
  }

I know the following is better but he said no loops

  int A = 0xAA000000;
  int B;

  __asm
  {
    mov eax, dword ptr [A] ;
    mov ebx,0 ;
    here:
    SHL eax,1 ;
    ADC ebx,0 ;
    CMP eax, 0
    JNE here
    MOV dword ptr [B],ebx ;
  }

codito ergo sum

[Stephen Hewitt]

The functions are inline - functions which are defined and not just declared in the class definition are implicitly inline. The operators involved compile down to very simple machine code instructions, for example:   /32 : sar eax,5   %32 : and eax,0000001Fh For a function which sets or clears a numbered bit there is no avoiding the &=, |= and << operators. As I said the MSVC6 implementation could be better:  - The constructors are not efficient.  - There is no specialization for the cases when the number of bits can fit into a machine word. If there was we could avoid the [], / and % operations in these cases in the set method. My main point however was to point out that the bitset doesn’t expand the data out to one byte per bit as you suggested. Also with a good implementation of STL and a decent compiler (I haven’t look under the hood of MCVC7’s STL) using a bitset is free (or close to). Steve

[BadKarma]

If you realy worry about cpu cycles you should write in asm or at least in inline assembly See my post here[^] I agree that in most situation the bitset will prefrom more then adequate. codito ergo sum -- modified at 18:28 Tuesday 7th March, 2006