//  std::hash and std::tr1::hash definitions, long double bits -*- C++ -*-

// Copyright (C) 2010 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/>.

  // For long double, careful with random padding bits (e.g., on x86,
  // 10 bytes -> 12 bytes) and resort to frexp.
  template<>
    size_t
    hash<long double>::operator()(long double __val) const
    {
      // 0 and -0 both hash to zero.
      if (__val == 0.0L)
	return 0;

      int __exponent;
      __val = __builtin_frexpl(__val, &__exponent);
      __val = __val < 0.0l ? -(__val + 0.5l) : __val;

      const long double __mult = __SIZE_MAX__ + 1.0l;
      __val *= __mult;

      // Try to use all the bits of the mantissa (really necessary only
      // on 32-bit targets, at least for 80-bit floating point formats).
      const size_t __hibits = (size_t)__val;
      __val = (__val - (long double)__hibits) * __mult;

      const size_t __coeff = __SIZE_MAX__ / __LDBL_MAX_EXP__;

      return __hibits + (size_t)__val + __coeff * __exponent;
    }
