From a61d1560c1a93c333b938ba5c0669e8a2c35c927 Mon Sep 17 00:00:00 2001
From: kruall <kruall@ydb.tech>
Date: Tue, 11 Feb 2025 19:33:37 +0300
Subject: [PATCH] Fix underflows in TValueHistory::Accumulate (#14442)

---
 ydb/library/actors/core/harmonizer/history.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/ydb/library/actors/core/harmonizer/history.h b/ydb/library/actors/core/harmonizer/history.h
index 889033dc7d84..a1cb3c0ed93e 100644
--- a/ydb/library/actors/core/harmonizer/history.h
+++ b/ydb/library/actors/core/harmonizer/history.h
@@ -34,6 +34,9 @@ struct TValueHistory {
     double Accumulate(auto op, auto comb, ui8 seconds) const {
         HARMONIZER_HISTORY_PRINT("Accumulate, seconds = ", static_cast<ui16>(seconds), ", WithTail = ", WithTail);
         double acc = AccumulatedValue;
+        if (seconds == 0) {
+            return acc;
+        }
         size_t idx = HistoryIdx;
         ui8 leftSeconds = seconds;
         if constexpr (!WithTail) {
@@ -46,10 +49,11 @@ struct TValueHistory {
         }
         HARMONIZER_HISTORY_PRINT("Accumulate iteration, acc = ", acc, ", idx = ", static_cast<ui16>(idx), ", leftSeconds = ", static_cast<ui16>(leftSeconds));
         while (leftSeconds) {
-            idx--;
             leftSeconds--;
-            if (idx >= HistoryBufferSize) {
+            if (idx == 0) {
                 idx = HistoryBufferSize - 1;
+            } else {
+                idx--;
             }
             if constexpr (!WithTail) {
                 acc = op(acc, History[idx]);