/*    Copyright 2012 10gen Inc.
 *
 *    This program is free software: you can redistribute it and/or  modify
 *    it under the terms of the GNU Affero General Public License, version 3,
 *    as published by the Free Software Foundation.
 *
 *    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 Affero General Public License for more details.
 *
 *    You should have received a copy of the GNU Affero General Public License
 *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the GNU Affero General Public License in all respects
 *    for all of the code used other than as permitted herein. If you modify
 *    file(s) with this exception, you may extend this exception to your
 *    version of the file(s), but you are not obligated to do so. If you do not
 *    wish to do so, delete this exception statement from your version. If you
 *    delete this exception statement from all source files in the program,
 *    then also delete it in the license file.
 */

/**
 * Implementation of the AtomicIntrinsics<T>::* operations for IA-32 and AMD64 systems using a
 * GCC-compatible compiler toolchain.
 */

#pragma once

#include <boost/utility.hpp>

namespace mongo {

    /**
     * Instantiation of AtomicIntrinsics<> for all word types T where sizeof<T> <= sizeof(void *).
     *
     * On 32-bit systems, this handles 8-, 16- and 32-bit word types.  On 64-bit systems,
     * it handles 8-, 16, 32- and 64-bit types.
     */
    template <typename T, typename IsTLarge=void>
    class AtomicIntrinsics {
    public:

        static T compareAndSwap(volatile T* dest, T expected, T newValue) {

            T result;
            asm volatile ("lock cmpxchg %[src], %[dest]"
                          : [dest] "+m" (*dest),
                            "=a" (result)
                          : [src] "r" (newValue),
                            "a" (expected)
                          : "memory", "cc");
            return result;
        }

        static T swap(volatile T* dest, T newValue) {

            T result = newValue;
            // No need for "lock" prefix on "xchg".
            asm volatile ("xchg %[r], %[dest]"
                          : [dest] "+m" (*dest),
                            [r] "+r" (result)
                          :
                          : "memory");
            return result;
        }

        static T load(volatile const T* value) {
            asm volatile ("mfence" ::: "memory");
            T result = *value;
            asm volatile ("mfence" ::: "memory");
            return result;
        }

        static T loadRelaxed(volatile const T* value) {
            return *value;
        }

        static void store(volatile T* dest, T newValue) {
            asm volatile ("mfence" ::: "memory");
            *dest = newValue;
            asm volatile ("mfence" ::: "memory");
        }

        static T fetchAndAdd(volatile T* dest, T increment) {

            T result = increment;
            asm volatile ("lock xadd %[src], %[dest]"
                          : [dest] "+m" (*dest),
                            [src] "+r" (result)
                          :
                          : "memory", "cc");
            return result;
        }

    private:
        AtomicIntrinsics();
        ~AtomicIntrinsics();
    };

    /**
     * Instantiation of AtomicIntrinsics<T> where sizeof<T> exceeds sizeof(void*).
     *
     * On 32-bit systems, this handles the 64-bit word type.  Not used on 64-bit systems.
     *
     * Note that the implementations of swap, store and fetchAndAdd spin until they succeed.  This
     * implementation is thread-safe, but may have poor performance in high-contention environments.
     * However, no superior solution exists for IA-32 (32-bit x86) systems.
     */
    template <typename T>
    class AtomicIntrinsics<T, typename boost::disable_if_c<sizeof(T) <= sizeof(void*)>::type> {
    public:
        static T compareAndSwap(volatile T* dest, T expected, T newValue) {
            T result = expected;
            asm volatile ("push %%eax\n"
                          "push %%ebx\n"
                          "push %%ecx\n"
                          "push %%edx\n"
                          "mov (%%edx), %%ebx\n"
                          "mov 4(%%edx), %%ecx\n"
                          "mov (%%edi), %%eax\n"
                          "mov 4(%%edi), %%edx\n"
                          "lock cmpxchg8b (%%esi)\n"
                          "mov %%eax, (%%edi)\n"
                          "mov %%edx, 4(%%edi)\n"
                          "pop %%edx\n"
                          "pop %%ecx\n"
                          "pop %%ebx\n"
                          "pop %%eax\n"
                          :
                          : "S" (dest),
                            "D" (&result),
                            "d" (&newValue)
                          : "memory", "cc");
            return result;
        }

        static T swap(volatile T* dest, T newValue) {

        T expected;
        T actual;
            do {
                expected = *dest;
                actual = compareAndSwap(dest, expected, newValue);
            } while (actual != expected);
            return actual;
        }

        static T load(volatile const T* value) {
            return compareAndSwap(const_cast<volatile T*>(value), T(0), T(0));
        }

        static void store(volatile T* dest, T newValue) {
            swap(dest, newValue);
        }

        static T fetchAndAdd(volatile T* dest, T increment) {

            T expected;
            T actual;
            do {
                expected = load(dest);
                actual = compareAndSwap(dest, expected, expected + increment);
            } while (actual != expected);
            return actual;
        }

    private:
        AtomicIntrinsics();
        ~AtomicIntrinsics();
    };

}  // namespace mongo