From e66f1df89d56983de0f7d1a70aa6e3ae0fe62730 Mon Sep 17 00:00:00 2001
From: Miroslav Lichvar <mlichvar@redhat.com>
Date: Wed, 11 May 2022 11:04:52 +0200
Subject: [PATCH] samplefilt: drop last sample in SPF_DropSamples()

When SPF_DropSamples() is called, don't keep the last sample to be
retrieved by SPF_GetLastSample(). It should be kept only after
filtering.
---
 samplefilt.c           | 16 +++++++++++++---
 test/unit/samplefilt.c |  1 +
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/samplefilt.c b/samplefilt.c
index 9cb892d..c3ee8b3 100644
--- a/samplefilt.c
+++ b/samplefilt.c
@@ -170,11 +170,21 @@ SPF_GetAvgSampleDispersion(SPF_Instance filter)
 
 /* ================================================== */
 
-void
-SPF_DropSamples(SPF_Instance filter)
+static void
+drop_samples(SPF_Instance filter, int keep_last)
 {
   filter->index = -1;
   filter->used = 0;
+  if (!keep_last)
+    filter->last = -1;
+}
+
+/* ================================================== */
+
+void
+SPF_DropSamples(SPF_Instance filter)
+{
+  drop_samples(filter, 0);
 }
 
 /* ================================================== */
@@ -405,7 +415,7 @@ SPF_GetFilteredSample(SPF_Instance filter, NTP_Sample *sample)
   if (!combine_selected_samples(filter, n, sample))
     return 0;
 
-  SPF_DropSamples(filter);
+  drop_samples(filter, 1);
 
   return 1;
 }
diff --git a/test/unit/samplefilt.c b/test/unit/samplefilt.c
index 20e6feb..22df125 100644
--- a/test/unit/samplefilt.c
+++ b/test/unit/samplefilt.c
@@ -103,6 +103,7 @@ test_unit(void)
 
       } else {
         SPF_DropSamples(filter);
+        TEST_CHECK(filter->last < 0);
       }
 
       TEST_CHECK(SPF_GetNumberOfSamples(filter) == 0);