From 3312405ada1ad4184c7552e41adfb1fdbd412c56 Mon Sep 17 00:00:00 2001
From: MikeChen <mike18913235447@gmail.com>
Date: Sat, 28 Jun 2025 14:35:18 +0800
Subject: [PATCH] Fix incorrect DROP_SIZE usage

Previously, measure() only recorded timings for indices in the middle
range [DROP_SIZE, N_MEASURES - DROP_SIZE), while update_statistics()
assumed all entries were starting available from index 10. This
mismatch allowed zero-valued exec_times from unmeasured head and tail
indices to be included in the t-test, reducing sample means, inflating
variances, and suppressing the t-value, which may lead to
incorrect results or prevent detection thresholds from being reached.

After the fix, all samples are measured and
update_statistics() discards DROP_SIZE samples at both ends. This
ensures correct sample accounting, prevents overestimating the number
of measurements required, and avoids false negatives due to
uninitialized timing data.

Change-Id: Ibb1515043da5f56d72fe34fd5c78e2283df9a993
---
 dudect/constant.c | 10 +++++-----
 dudect/fixture.c  |  2 +-
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/dudect/constant.c b/dudect/constant.c
index f6f1e95eb..976000d8b 100644
--- a/dudect/constant.c
+++ b/dudect/constant.c
@@ -77,7 +77,7 @@ bool measure(int64_t *before_ticks,
 
     switch (mode) {
     case DUT(insert_head):
-        for (size_t i = DROP_SIZE; i < N_MEASURES - DROP_SIZE; i++) {
+        for (size_t i = 0; i < N_MEASURES; i++) {
             char *s = get_random_string();
             dut_new();
             dut_insert_head(
@@ -94,7 +94,7 @@ bool measure(int64_t *before_ticks,
         }
         break;
     case DUT(insert_tail):
-        for (size_t i = DROP_SIZE; i < N_MEASURES - DROP_SIZE; i++) {
+        for (size_t i = 0; i < N_MEASURES; i++) {
             char *s = get_random_string();
             dut_new();
             dut_insert_head(
@@ -111,7 +111,7 @@ bool measure(int64_t *before_ticks,
         }
         break;
     case DUT(remove_head):
-        for (size_t i = DROP_SIZE; i < N_MEASURES - DROP_SIZE; i++) {
+        for (size_t i = 0; i < N_MEASURES; i++) {
             dut_new();
             dut_insert_head(
                 get_random_string(),
@@ -129,7 +129,7 @@ bool measure(int64_t *before_ticks,
         }
         break;
     case DUT(remove_tail):
-        for (size_t i = DROP_SIZE; i < N_MEASURES - DROP_SIZE; i++) {
+        for (size_t i = 0; i < N_MEASURES; i++) {
             dut_new();
             dut_insert_head(
                 get_random_string(),
@@ -147,7 +147,7 @@ bool measure(int64_t *before_ticks,
         }
         break;
     default:
-        for (size_t i = DROP_SIZE; i < N_MEASURES - DROP_SIZE; i++) {
+        for (size_t i = 0; i < N_MEASURES; i++) {
             dut_new();
             dut_insert_head(
                 get_random_string(),
diff --git a/dudect/fixture.c b/dudect/fixture.c
index bf6ce8f31..34bc551e9 100644
--- a/dudect/fixture.c
+++ b/dudect/fixture.c
@@ -103,7 +103,7 @@ static void update_statistics(const int64_t *exec_times,
                               uint8_t *classes,
                               int64_t *percentiles)
 {
-    for (size_t i = 0; i < N_MEASURES; i++) {
+    for (size_t i = DROP_SIZE; i < N_MEASURES - DROP_SIZE; i++) {
         int64_t difference = exec_times[i];
         /* CPU cycle counter overflowed or dropped measurement */
         if (difference <= 0)