From af81088cf938f388dac201a90b8ef221ee82aef6 Mon Sep 17 00:00:00 2001
From: Gertjan van den Burg <burg@ese.eur.nl>
Date: Thu, 6 Oct 2016 17:42:41 +0200
Subject: change timer functionality to use clock_monotonic_raw

---
 src/gensvm_timer.c | 34 +++++++++++++++++++++++++++-------
 1 file changed, 27 insertions(+), 7 deletions(-)

(limited to 'src/gensvm_timer.c')

diff --git a/src/gensvm_timer.c b/src/gensvm_timer.c
index 04d93b1..0e020fe 100644
--- a/src/gensvm_timer.c
+++ b/src/gensvm_timer.c
@@ -1,25 +1,45 @@
 /**
- * @file timer.c
+ * @file gensvm_timer.c
  * @author Gertjan van den Burg
  * @date January, 2014
  * @brief Utility functions relating to time
  *
  * @details
  * This file contains a simple function for calculating the time in seconds
- * elapsed between two clock() calls.
+ * elapsed between two Timer() calls.
  *
  */
 
 #include "gensvm_timer.h"
 
 /**
- * @brief Calculate the time between two clocks
+ * @brief Calculate the time between two time recordings
  *
- * @param[in] 	s_time 	starting time
- * @param[in] 	e_time 	end time
+ * @detail
+ * This function should be used with time recordings done by clock_gettime() 
+ * using CLOCK_MONOTONIC_RAW. For this, the Timer() macro has been defined in 
+ * the header file. Example usage:
+ *
+ * @code
+ * struct timespec start, stop;
+ * Timer(start);
+ * // do some work //
+ * Timer(stop);
+ * double duration = gensvm_elapsed_time(&start, &stop);
+ * @endcode
+ *
+ * This approach to measuring time has been chosen since CLOCK_MONOTONIC_RAW 
+ * is guaranteed to be monotonically increasing, and is not affected by leap 
+ * seconds or other changes to the system clock. It is therefore thread-safe 
+ * and can be used to accurately measure time intervals.
+ *
+ * @param[in] 	start 	starting time
+ * @param[in] 	stop 	end time
  * @returns 		time elapsed in seconds
  */
-double gensvm_elapsed_time(clock_t s_time, clock_t e_time)
+double gensvm_elapsed_time(struct timespec *start, struct timespec *stop)
 {
-	return ((double) (e_time - s_time))/((double) CLOCKS_PER_SEC);
+	double delta_s = stop->tv_sec - start->tv_sec;
+	double delta_ns = stop->tv_nsec - start->tv_nsec;
+	return delta_s + delta_ns * 1e-9;
 }
-- 
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