Display median ping time

cnping.c

@@ -417,6 +417,91 @@ void DrawFrameHistogram()
 	return;
 }
 
+// algorithm from here: https://stackoverflow.com/a/7477879
+// cites: "Algorithm from Numerical recipes in C of 1992"
+// Also from here published in the public domain http://ndevilla.free.fr/median/median/src/quickselect.c
+#ifndef ELEM_SWAP(a, b)
+#define ELEM_SWAP(a, b) { register double t=(a);(a)=(b);(b)=t; }
+#endif
+
+double QuickSelectMedian( double arr[], uint16_t n )
+{
+	uint16_t low, high;
+	uint16_t median;
+	uint16_t middle, ll, hh;
+	low = 0;
+	high = n - 1;
+	median = (low + high) / 2;
+	for ( ;; )
+	{
+		if ( high <= low ) /* One element only */
+			return arr[median];
+		if ( high == low + 1 )
+		{ /* Two elements only */
+			if ( arr[low] > arr[high] )
+				ELEM_SWAP( arr[low], arr[high] );
+			return arr[median];
+		}
+		/* Find median of low, middle and high items; swap into position low */
+		middle = (low + high) / 2;
+		if ( arr[middle] > arr[high] )
+			ELEM_SWAP( arr[middle], arr[high] );
+		if ( arr[low] > arr[high] )
+			ELEM_SWAP( arr[low], arr[high] );
+		if ( arr[middle] > arr[low] )
+			ELEM_SWAP( arr[middle], arr[low] );
+		/* Swap low item (now in position middle) into position (low+1) */
+		ELEM_SWAP( arr[middle], arr[low + 1] );
+		/* Nibble from each end towards middle, swapping items when stuck */
+		ll = low + 1;
+		hh = high;
+		for ( ;; )
+		{
+			do ll++; while ( arr[low] > arr[ll] );
+			do hh--; while ( arr[hh] > arr[low] );
+			if ( hh < ll )
+				break;
+			ELEM_SWAP( arr[ll], arr[hh] );
+		}
+		/* Swap middle item (in position low) back into correct position */
+		ELEM_SWAP( arr[low], arr[hh] );
+		/* Re-set active partition */
+		if ( hh <= median )
+			low = ll;
+		if ( hh >= median )
+			high = hh - 1;
+	}
+	return arr[median];
+}
+
+double GetMedianPing()
+{
+	//create array of valid ping times
+	double *validPingsArr = malloc( screenx * sizeof( double ));
+	size_t nValidPings = 0;
+
+	for ( size_t i = 0; i < screenx; i++ )
+	{
+		int index = ((current_cycle - i - 1) + PINGCYCLEWIDTH) & (PINGCYCLEWIDTH - 1);
+		double st = PingSendTimes[index];
+		double rt = PingRecvTimes[index];
+
+		if ( rt > st ) // ping received
+		{
+			double dt = rt - st;
+			dt *= 1000;
+			validPingsArr[nValidPings++] = dt;
+		}
+	}
+
+	// calculate median
+	double result = 0;
+	if ( nValidPings > 0 )
+		result = QuickSelectMedian( validPingsArr, nValidPings );
+	free( validPingsArr );
+
+	return result;
+}
 
 void DrawFrame( void )
 {
@@ -479,6 +564,7 @@ void DrawFrame( void )
 	}
 
 	double avg = totaltime / totalcountok;
+	double median = GetMedianPing();
 	loss = (double) totalcountloss / (totalcountok + totalcountloss) * 100;
 
 	for( i = 0; i < screenx; i++ )
@@ -522,12 +608,13 @@ void DrawFrame( void )
 		"Max :%6.2f ms    Historical max:   %5.2f ms\n"
 		"Avg :%6.2f ms    Biggest interval: %5.2f ms\n"
 #ifdef WIN32
-		"Std :%6.2f ms    Historical loss:  %I64u/%I64u %5.3f%%\n"
+		"Med :%6.2f ms    Historical loss:  %I64u/%I64u %5.3f%%\n"
 #else
-		"Std :%6.2f ms    Historical loss:  %lu/%lu %5.3f%%\n"
+		"Med :%6.2f ms    Historical loss:  %lu/%lu %5.3f%%\n"
 #endif
-		"Loss:%6.1f %%", last, pinghost, mintime, maxtime, globmaxtime*1000, avg, globinterval*1000.0, stddev,
-		globallost, globalrx+globallost, globallost*100.0f/(globalrx+globallost), loss );
+		"Std :%6.2f ms\n"
+		"Loss:%6.1f %%", last, pinghost, mintime, maxtime, globmaxtime*1000, avg, globinterval*1000.0, median,
+		globallost, globalrx+globallost, globallost*100.0f/(globalrx+globallost), stddev, loss );
 
 	DrawMainText( stbuf );
 	OGUSleep( 1000 );