Add timestamps to libdivecomputer.log

Since I learned while trying to implement this that getting sub-second
resolution time in portable C99 is hard (especially for someone who is
used to the comfort of std::chrono and Howard Hinnants date library) the
timer-implemetation from libdivecomputer is now copied to the subsurface
source.

Signed-off-by: Christof Arnosti <charno@charno.ch>

core/timer.c

@@ -0,0 +1,161 @@
+/*
+ * libdivecomputer
+ *
+ * Copyright (C) 2018 Jef Driesen
+ *
+ * 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., 51 Franklin Street, Fifth Floor, Boston,
+ * MA 02110-1301 USA
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <stdlib.h>
+
+#ifdef _WIN32
+#define NOGDI
+#include <windows.h>
+#else
+#include <time.h>
+#include <sys/time.h>
+#ifdef HAVE_MACH_MACH_TIME_H
+#include <mach/mach_time.h>
+#endif
+#endif
+
+#include "timer.h"
+
+struct dc_timer_t {
+#if defined (_WIN32)
+	LARGE_INTEGER timestamp;
+	LARGE_INTEGER frequency;
+#elif defined (HAVE_CLOCK_GETTIME)
+	struct timespec timestamp;
+#elif defined (HAVE_MACH_ABSOLUTE_TIME)
+	uint64_t timestamp;
+	mach_timebase_info_data_t info;
+#else
+	struct timeval timestamp;
+#endif
+};
+
+dc_status_t
+dc_timer_new (dc_timer_t **out)
+{
+	dc_timer_t *timer = NULL;
+
+	if (out == NULL)
+		return DC_STATUS_INVALIDARGS;
+
+	timer = (dc_timer_t *) malloc (sizeof (dc_timer_t));
+	if (timer == NULL) {
+		return DC_STATUS_NOMEMORY;
+	}
+
+#if defined (_WIN32)
+	if (!QueryPerformanceFrequency(&timer->frequency) ||
+		!QueryPerformanceCounter(&timer->timestamp)) {
+		free(timer);
+		return DC_STATUS_IO;
+	}
+#elif defined (HAVE_CLOCK_GETTIME)
+	if (clock_gettime(CLOCK_MONOTONIC, &timer->timestamp) != 0) {
+		free(timer);
+		return DC_STATUS_IO;
+	}
+#elif defined (HAVE_MACH_ABSOLUTE_TIME)
+	if (mach_timebase_info(&timer->info) != KERN_SUCCESS) {
+		free(timer);
+		return DC_STATUS_IO;
+	}
+
+	timer->timestamp = mach_absolute_time();
+#else
+	if (gettimeofday (&timer->timestamp, NULL) != 0) {
+		free(timer);
+		return DC_STATUS_IO;
+	}
+#endif
+
+	*out = timer;
+
+	return DC_STATUS_SUCCESS;
+}
+
+dc_status_t
+dc_timer_now (dc_timer_t *timer, dc_usecs_t *usecs)
+{
+	dc_status_t status = DC_STATUS_SUCCESS;
+	dc_usecs_t value = 0;
+
+	if (timer == NULL) {
+		status = DC_STATUS_INVALIDARGS;
+		goto out;
+	}
+
+#if defined (_WIN32)
+	LARGE_INTEGER now;
+	if (!QueryPerformanceCounter(&now)) {
+		status = DC_STATUS_IO;
+		goto out;
+	}
+
+	value = (now.QuadPart - timer->timestamp.QuadPart) * 1000000 / timer->frequency.QuadPart;
+#elif defined (HAVE_CLOCK_GETTIME)
+	struct timespec now, delta;
+	if (clock_gettime(CLOCK_MONOTONIC, &now) != 0) {
+		status = DC_STATUS_IO;
+		goto out;
+	}
+
+	if (now.tv_nsec < timer->timestamp.tv_nsec) {
+		delta.tv_nsec = 1000000000 + now.tv_nsec - timer->timestamp.tv_nsec;
+		delta.tv_sec = now.tv_sec - timer->timestamp.tv_sec - 1;
+	} else {
+		delta.tv_nsec = now.tv_nsec - timer->timestamp.tv_nsec;
+		delta.tv_sec = now.tv_sec - timer->timestamp.tv_sec;
+	}
+
+	value = (dc_usecs_t) delta.tv_sec * 1000000 + delta.tv_nsec / 1000;
+#elif defined (HAVE_MACH_ABSOLUTE_TIME)
+	uint64_t now = mach_absolute_time();
+	value = (now - timer->timestamp) * timer->info.numer / (timer->info.denom * 1000);
+#else
+	struct timeval now, delta;
+	if (gettimeofday (&now, NULL) != 0) {
+		status = DC_STATUS_IO;
+		goto out;
+	}
+
+	timersub (&now, &timer->timestamp, &delta);
+
+	value = (dc_usecs_t) delta.tv_sec * 1000000 + delta.tv_usec;
+#endif
+
+out:
+	if (usecs)
+		*usecs = value;
+
+	return status;
+}
+
+dc_status_t
+dc_timer_free (dc_timer_t *timer)
+{
+	free (timer);
+
+	return DC_STATUS_SUCCESS;
+}