/*
 * This file is distributed as part of the MariaDB Corporation MaxScale.  It 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,
 * version 2.
 *
 * 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., 51
 * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Copyright MariaDB Corporation Ab 2013-2014
 */

/**
 * @file atomic.c  - Implementation of atomic opertions for the gateway
 *
 * @verbatim
 * Revision History
 *
 * Date		Who		Description
 * 10/06/13	Mark Riddoch	Initial implementation
 *
 * @endverbatim
 */

/**
 * Implementation of an atomic add operation for the GCC environment, or the 
 * X86 processor.  If we are working within GNU C then we can use the GCC
 * atomic add built in function, which is portable across platforms that
 * implement GCC.  Otherwise, this function currently supports only X86
 * architecture (without further development).
 * 
 * Adds a value to the contents of a location pointed to by the first parameter.
 * The add operation is atomic and the return value is the value stored in the 
 * location prior to the operation. The number that is added may be signed, 
 * therefore atomic_subtract is merely an atomic add with a negative value.
 *
 * @param variable	Pointer the the variable to add to
 * @param value		Value to be added
 * @return		The value of variable before the add occurred
 */
int
atomic_add(int *variable, int value)
{
#ifdef __GNUC__
        return (int) __sync_fetch_and_add (variable, value);
#else    
	asm volatile(
		"lock; xaddl %%eax, %2;"
		:"=a" (value)
		: "a" (value), "m" (*variable)
		: "memory" );
	return value;
#endif
}