gr_count_bits.cc

这是用python语言写的一个数字广播的信号处理工具包。利用它

/* -*- c++ -*- */
/*
 * Copyright 2003 Free Software Foundation, Inc.
 * 
 * This file is part of GNU Radio
 * 
 * GNU Radio is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3, or (at your option)
 * any later version.
 * 
 * GNU Radio is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with GNU Radio; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#include <gr_count_bits.h>

/*
 * these are slow and obvious.  If you need something faster, fix these
 */

// return number of set bits in the low  8 bits of x
unsigned int 
gr_count_bits8 (unsigned int x)
{
  int	count = 0;

  for (int i = 0; i < 8; i++)
    if (x & (1 << i))
      count++;

  return count;
}

// return number of set bits in the low 16 bits of x
unsigned int 
gr_count_bits16 (unsigned int x)
{
  int	count = 0;

  for (int i = 0; i < 16; i++)
    if (x & (1 << i))
      count++;

  return count;

}


#if 0	// slow and obvious

// return number of set bits in the low 32 bits of x
unsigned int 
gr_count_bits32 (unsigned int x)
{
  int	count = 0;

  for (int i = 0; i < 32; i++)
    if (x & (1 << i))
      count++;

  return count;
}

#else	// fast and not so obvious

// return number of set bits in the low 32 bits of x
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);
}

#endif
 

// return number of set bits in the low 64 bits of x
unsigned int
gr_count_bits64 (unsigned long long x)
{
  return gr_count_bits32((x >> 32) & 0xffffffff) + gr_count_bits32(x & 0xffffffff);
}