int128_compatibility.hpp

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#ifndef LIBJMMCG_CORE_INT128_COMPATIBILITY_HPP
#define LIBJMMCG_CORE_INT128_COMPATIBILITY_HPP
 
/******************************************************************************
 * * Copyright © 2021 by J.M.McGuiness, coder@hussar.me.uk
 **
 ** This library is free software; you can redistribute it and/or
 ** modify it under the terms of the GNU Lesser General Public
 ** License as published by the Free Software Foundation; either
 ** version 2.1 of the License, 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
 ** Lesser General Public License for more details.
 **
 ** You should have received a copy of the GNU Lesser General Public
 ** License along with this library; if not, write to the Free Software
 ** Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
 
#include <cassert>
#include <cstdint>
 
/**
 * \file For those architectures that do not support 128-bit integer types as builtins, e.g. ARM & many 32-bit platforms.
 */
 
namespace jmmcg { namespace LIBJMMCG_VER_NAMESPACE {
 
#ifdef __SIZEOF_INT128__
   using int128_t=__int128;
   using uint128_t=__uint128_t;
 
   inline unsigned
   count_trailing_zeroes_compat(const uint128_t value) noexcept(true) {
      assert(value!=0);
      return __builtin_ctzll(value);
   }
 
   inline unsigned
   count_leading_zeroes_compat(const uint128_t value) noexcept(true) {
      assert(value!=0);
      return __builtin_clzll(value);
   }
 
#else
   struct int128_t {
      std::uint64_t low;
      std::int64_t high;
   } __attribute__((packed));
   struct uint128_t {
      std::uint64_t low;
      std::uint64_t high;
 
      constexpr bool
      operator==(std::uint64_t rhs) const noexcept(true) {
         return high==0 && low<rhs;
      }
      constexpr bool
      operator!=(std::uint64_t rhs) const noexcept(true) {
         return !this->operator==(rhs);
      }
      constexpr bool
      operator<(uint128_t const &rhs) const noexcept(true) {
         return high<rhs.high
         || (
            high==rhs.high && low<rhs.low
         );
      }
 
      constexpr uint128_t &
      operator~() noexcept(true) {
         low=~low;
         high=~high;
         return *this;
      }
      constexpr uint128_t &
      operator&=(uint128_t const &rhs) noexcept(true) {
         low&=rhs.low;
         high&=rhs.high;
         return *this;
      }
      constexpr uint128_t
      operator>>(std::size_t const shift) const noexcept(true) {
         assert(shift<=128);
         if (shift>=64) {
            uint128_t tmp{high, 0};
            assert(tmp<*this);
            return tmp>>(shift-64);
         } else {
            const uint128_t tmp{
               (high<<(64-shift)) | (low>>shift),
               (high>>shift)
            };
            assert(tmp<*this);
            return tmp;
         }
      }
   } __attribute__((packed));
 
   inline unsigned
   count_trailing_zeroes_compat(const uint128_t value) noexcept(true) {
      assert(value.high!=0 || value.low!=0);
      return __builtin_ctzll(value.high)+__builtin_ctzll(value.low);
   }
 
   inline unsigned
   count_leading_zeroes_compat(const uint128_t value) noexcept(true) {
      assert(value.high!=0 || value.low!=0);
      return __builtin_clzll(value.high)+__builtin_clzll(value.low);
   }
 
#endif
 
} }
 
#endif