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    /* vim: set tabstop=4 expandtab shiftwidth=4 softtabstop=4: */
    
    /*
     * Copyright 2015 University of Piemonte Orientale, Computer Science Institute
     *
     * This file is part of UPOalglib.
     *
     * UPOalglib 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 of the License, or
     * (at your option) any later version.
     *
     * UPOalglib 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 UPOalglib.  If not, see <http://www.gnu.org/licenses/>.
     */
    
    #include <assert.h>
    #include "hires_timer_private.h"
    #include <stdlib.h>
    #include <sys/time.h>
    #include <time.h>
    #include <upo/error.h>
    
    
    #define UPO_HIRES_TIMER_MICROSECONDS_PER_SECOND 1e+6
    
    
    upo_hires_timer_t upo_hires_timer_create()
    {
        upo_hires_timer_t timer;
        timer = malloc(sizeof(struct upo_hires_timer_s));
        if (timer == NULL)
        {
            upo_throw_sys_error("Unable to allocate memory for the high-resolution timer");
        }
    
        /* Invalidates the timer */
        timer->start.tv_sec = timer->start.tv_usec
                            = timer->stop.tv_sec
                            = timer->stop.tv_usec
                            = -1;
    
        return timer;
    }
    
    void upo_hires_timer_destroy(upo_hires_timer_t timer)
    {
        if (timer != NULL)
        {
            free(timer);
        }
    }
    
    void upo_hires_timer_start(upo_hires_timer_t timer)
    {
        int ret;
    
        assert( timer != NULL );
    
        ret = gettimeofday(&timer->start, NULL);
        if (ret == -1)
        {
            upo_throw_sys_error("Unable to start the high-resolution timer");
        }
    
        timer->stop.tv_sec = timer->stop.tv_usec
                           = -1; 
    }
    
    void upo_hires_timer_stop(upo_hires_timer_t timer)
    {
        assert( timer != NULL );
    
        if (!upo_hires_timer_is_stopped(timer))
        {
            int ret;
            ret = gettimeofday(&timer->stop, NULL);
            if (ret == -1)
            {
                upo_throw_sys_error("Unable to stop the high-resolution timer");
            }
        }
    } 
    
    int upo_hires_timer_is_started(const upo_hires_timer_t timer) 
    {
        assert( timer != NULL );
    
        return (timer->start.tv_sec != -1 && timer->start.tv_usec != -1) ? 1 : 0;
    }
    
    int upo_hires_timer_is_stopped(const upo_hires_timer_t timer) 
    {
        assert( timer != NULL );
    
        return (timer->stop.tv_sec != -1 && timer->stop.tv_usec != -1) ? 1 : 0;
    }
    
    double upo_hires_timer_elapsed(const upo_hires_timer_t timer)
    {
        assert( timer != NULL );
    
        if (upo_hires_timer_is_stopped(timer))
        {
            /* The timer is stopped: returns the length of the [start,stop) interval */
            return difftime(timer->stop.tv_sec, timer->start.tv_sec)
                   + difftime(timer->stop.tv_usec, timer->start.tv_usec)/UPO_HIRES_TIMER_MICROSECONDS_PER_SECOND;
        }
    
        if (upo_hires_timer_is_started(timer))
        {
            /* The timer isn't stopped: returns the time elapsed so far */
    
            struct timeval now;
            int ret;
    
            ret = gettimeofday(&now, NULL);
            if (ret == -1)
            {
                upo_throw_sys_error("Unable to get elapsed time for the high-resolution timer");
            }
    
            return difftime(now.tv_sec, timer->start.tv_sec)
                   + difftime(now.tv_usec, timer->start.tv_usec)/UPO_HIRES_TIMER_MICROSECONDS_PER_SECOND;
        }
    
        return -1;
    }