bitcount.h

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// Copyright (C) 1997-2020 by Pawel Pilarczyk.
//
// This file is part of my research software package. This 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 of the License, or (at your option) any later version.
//
// This software 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 this software; see the file "license.txt". If not,
// please, see <https://www.gnu.org/licenses/>.
 
// Started on November 29, 2005. Last revision: November 29, 2005.
 
 
#ifndef _CHOMP_STRUCT_BITCOUNT_H_
#define _CHOMP_STRUCT_BITCOUNT_H_
 
namespace chomp {
namespace homology {
 
 
extern unsigned char bitcounttable [];
 
inline int bitcountbyte (char n)
{
        return bitcounttable [static_cast<unsigned char> (n)];
} /* bitcountbyte */
 
inline int bitcount (int number)
{
        if (!number)
                return 0;
        unsigned int n = static_cast<unsigned int> (number);
        if (n < 256)
                return bitcountbyte (static_cast<unsigned char> (n));
        int c = 0;
        while (n > 255)
        {
                if (n & 1)
                        ++ c;
                n >>= 1;
        }
        return c + bitcountbyte (static_cast<unsigned char> (n));
} /* bitcount */
 
 
} // namespace homology
} // namespace chomp
 
#endif // _CHOMP_STRUCT_BITCOUNT_H_