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[EDIT] FILE: hash_fun.h

// 'struct hash' from SGI -*- C++ -*-

// Copyright (C) 2001-2018 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library 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.

// This library 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.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/*
 * Copyright (c) 1996-1998
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 *
 * Copyright (c) 1994
 * Hewlett-Packard Company
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Hewlett-Packard Company makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 */

/** @file backward/hash_fun.h
 *  This file is a GNU extension to the Standard C++ Library (possibly
 *  containing extensions from the HP/SGI STL subset).
 */

#ifndef _BACKWARD_HASH_FUN_H
#define _BACKWARD_HASH_FUN_H 1

#include <bits/c++config.h>

namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

using std::size_t;

template<class _Key>
    struct hash { };

inline size_t
  __stl_hash_string(const char* __s)
  {
    unsigned long __h = 0;
    for ( ; *__s; ++__s)
      __h = 5 * __h + *__s;
    return size_t(__h);
  }

template<>
    struct hash<char*>
    {
      size_t
      operator()(const char* __s) const
      { return __stl_hash_string(__s); }
    };

template<>
    struct hash<const char*>
    {
      size_t
      operator()(const char* __s) const
      { return __stl_hash_string(__s); }
    };

template<>
    struct hash<char>
    { 
      size_t
      operator()(char __x) const
      { return __x; }
    };

template<>
    struct hash<unsigned char>
    { 
      size_t
      operator()(unsigned char __x) const
      { return __x; }
    };

template<>
    struct hash<signed char>
    {
      size_t
      operator()(unsigned char __x) const
      { return __x; }
    };

template<>
    struct hash<short>
    {
      size_t
      operator()(short __x) const
      { return __x; }
    };

template<>
    struct hash<unsigned short>
    {
      size_t
      operator()(unsigned short __x) const
      { return __x; }
    };

template<>
    struct hash<int>
    { 
      size_t 
      operator()(int __x) const 
      { return __x; }
    };

template<>
    struct hash<unsigned int>
    { 
      size_t
      operator()(unsigned int __x) const
      { return __x; }
    };

template<>
    struct hash<long>
    {
      size_t
      operator()(long __x) const
      { return __x; }
    };

template<>
    struct hash<unsigned long>
    {
      size_t
      operator()(unsigned long __x) const
      { return __x; }
    };

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif

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