/*
* Copyright (c), MM Weiss
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* 3. Neither the name of the MM Weiss nor the names of its contributors
* may be used to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
* SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
* OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
* TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

/*
* clock_gettime_stub.c
* gcc -Wall -c clock_gettime_stub.c
* posix realtime functions; MacOS user space glue
*/

/* @comment
* other possible implementation using intel builtin rdtsc
* rdtsc-workaround: http://www.mcs.anl.gov/~kazutomo/rdtsc.html
*
* we could get the ticks by doing this
*
* __asm __volatile("mov %%ebx, %%esi\n\t"
* "cpuid\n\t"
* "xchg %%esi, %%ebx\n\t"
* "rdtsc"
* : "=a" (a),
* "=d" (d)
* );

* we could even replace our tricky sched_yield call by assembly code to get a better accurency,
* anyway the following C stub will satisfy 99% of apps using posix clock_gettime call,
* moreover, the setter version (clock_settime) could be easly written using mach primitives:
* http://www.opensource.apple.com/source/xnu/xnu-${VERSION}/osfmk/man/ (clock_[set|get]_time)
*
* hackers don't be crackers, don't you use a flush toilet?
*
*
* @see draft: ./posix-realtime-stub/posix-realtime-stub.c
*
*/

extern "C" {

#ifndef _GETTIME_H
#define _GETTIME_H

#ifdef __APPLE__

#pragma weak clock_gettime

#include <sys/time.h>
#include <sys/resource.h>
#include <mach/mach.h>
#include <mach/clock.h>
#include <mach/mach_time.h>
#include <errno.h>
#include <unistd.h>
#include <sched.h>

typedef enum {
    CLOCK_REALTIME,
    CLOCK_MONOTONIC,
    CLOCK_PROCESS_CPUTIME_ID,
    CLOCK_THREAD_CPUTIME_ID
} clockid_t;

static mach_timebase_info_data_t __clock_gettime_inf;

int clock_gettime(clockid_t clk_id, struct timespec *tp) {
    kern_return_t ret;
    clock_serv_t clk;
    clock_id_t clk_serv_id;
    mach_timespec_t tm;

    uint64_t start, end, delta, nano;

  	
    int retval = -1;
	switch (clk_id) {
	    case CLOCK_REALTIME:
	    case CLOCK_MONOTONIC:
	        clk_serv_id = clk_id == CLOCK_REALTIME ? CALENDAR_CLOCK : SYSTEM_CLOCK;
	        if (KERN_SUCCESS == (ret = host_get_clock_service(mach_host_self(), clk_serv_id, &clk))) {
	            if (KERN_SUCCESS == (ret = clock_get_time(clk, &tm))) {
	                tp->tv_sec = tm.tv_sec;
	                tp->tv_nsec = tm.tv_nsec;
	                retval = 0;
	             }
	         }
	         if (KERN_SUCCESS != ret) {
	             errno = EINVAL;
	             retval = -1;
	         }
	    break;
	    case CLOCK_PROCESS_CPUTIME_ID:
	    case CLOCK_THREAD_CPUTIME_ID:
	        start = mach_absolute_time();
	        if (clk_id == CLOCK_PROCESS_CPUTIME_ID) {
	            getpid();
	        } else {
	            sched_yield();
	        }
	    end = mach_absolute_time();
	    delta = end - start;
	    if (0 == __clock_gettime_inf.denom) {
	        mach_timebase_info(&__clock_gettime_inf);
	    }
	    nano = delta * __clock_gettime_inf.numer / __clock_gettime_inf.denom;
	    tp->tv_sec = nano * 1e-9;
	    tp->tv_nsec = nano - (tp->tv_sec * 1e9);
	    retval = 0;
	break;
	default:
	    errno = EINVAL;
	    retval = -1;
	}
	return retval;
}
	
#endif // __APPLE__
#endif // _GETTIME_H
	
}