utils.h

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/*
 *  Copyright (C) 2001-2017 Stefan Weinzierl
 *
 *  This program 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 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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 program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
 
#ifndef __NESTEDSUMS_UTILS_H__
#define __NESTEDSUMS_UTILS_H__
 
#include <typeinfo>
 
#include "ginac/ginac.h"
 
#include "config.h"
 
namespace nestedsums {
 
// some functions stolen from GiNaC:
 
inline unsigned rotate_left_31(unsigned n)
{
        // clear highest bit and shift 1 bit to the left
        n = (n & 0x7FFFFFFFU) << 1;
        
        // overflow? clear highest bit and set lowest bit
        if (n & 0x80000000U)
                n = (n & 0x7FFFFFFFU) | 0x00000001U;
        
        GINAC_ASSERT(n<0x80000000U);
        
        return n;
}
 
#if SIZEOF_VOID_P == SIZEOF_INT
typedef unsigned int p_int;
#elif SIZEOF_VOID_P == SIZEOF_LONG
typedef unsigned long p_int;
#elif SIZEOF_VOID_P == SIZEOF_LONG_LONG
typedef unsigned long long p_int;
#else
typedef unsigned long p_int;
#endif
 
inline unsigned golden_ratio_hash(unsigned n)
{
        // This function requires arithmetic with at least 64 significant bits
#if SIZEOF_LONG >= 8
        // So 'long' has 64 bits.  Excellent!  We prefer it because it might be
        // more efficient than 'long long'.
        unsigned long l = n * 0x4f1bbcddL;
        return (l & 0x7fffffffU) ^ (l >> 32);
#elif SIZEOF_LONG_LONG >= 8
        // This requires 'long long' (or an equivalent 64 bit type)---which is,
        // unfortunately, not ANSI-C++-compliant.
        // (Yet C99 demands it, which is reason for hope.)
        unsigned long long l = n * 0x4f1bbcddL;
        return (l & 0x7fffffffU) ^ (l >> 32);
#elif SIZEOF_LONG_DOUBLE > 8
        // If 'long double' is bigger than 64 bits, we assume that the mantissa
        // has at least 64 bits. This is not guaranteed but it's a good guess.
        // Unfortunately, it may lead to horribly slow code.
        const static long double golden_ratio = .618033988749894848204586834370;
        long double m = golden_ratio * n;
        return unsigned((m - int(m)) * 0x80000000);
#else
#error "No 64 bit data type. You lose."
#endif
}
 
static inline unsigned make_hash_seed(const std::type_info& tinfo)
{
        // this pointer is the same for all objects of the same type.
        // Hence we can use that pointer 
        const void* mangled_name_ptr = (const void*)tinfo.name();
        unsigned v = golden_ratio_hash((p_int)mangled_name_ptr);
        return v;
}
 
 
} // namespace nestedsums
 
#endif // ndef __NESTEDSUMS_UTILS_H__