Re: [Discuss-gnuradio] Help using simple_framer and simple_correlator

[Stephane Fillod]

> > Nor can I make out how this code counts bits?
> > 
> > // return number of set bits in the low 32 bits of x
> > int 
> > gr_count_bits32 (int x)
> > {
> >   int       count = 0;
> > 
> >   for (int i = 0; i < 32; i++)
> >     if (x & (1 << i))
> >       count++;
> > 
> >   return count;
> > }

This is also known as the hamming weight (i.e. the number
of bits set) of a 32-bit word. Here is a faster algorithm:

unsigned int
gr_count_bits32 (unsigned int x)
{
  unsigned res = (x & 0x55555555) + ((x >> 1) & 0x55555555);
  res = (res & 0x33333333) + ((res >> 2) & 0x33333333);
  res = (res & 0x0F0F0F0F) + ((res >> 4) & 0x0F0F0F0F);
  res = (res & 0x00FF00FF) + ((res >> 8) & 0x00FF00FF);
  return (res & 0x0000FFFF) + ((res >> 16) & 0x0000FFFF);
}

-- 
Stephane