From a4162b6086586954dbc65e452518a4355c48a253 Mon Sep 17 00:00:00 2001
From: Ganesh Patil <7030871503ganeshpatil@gmail.com>
Date: Tue, 24 Feb 2026 09:36:23 +0530
Subject: [PATCH] fix: clamp lag parameter to buffer size with warning (fixes
 #379)

The circular buffer in plotymlag.py has a fixed size of 10. When a user
sets lag >= size via tryparam, the modulo arithmetic silently wraps,
producing incorrect data (e.g., lag=15 behaves like lag=5).

Add input validation that clamps lag to size-1 and emits a
logging.warning when the requested value exceeds the buffer capacity.
This prevents silent data corruption while preserving backward
compatibility and the existing circular buffer logic.
---
 tools/plotymlag.py | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/plotymlag.py b/tools/plotymlag.py
index 96b5bf8..264a98d 100644
--- a/tools/plotymlag.py
+++ b/tools/plotymlag.py
@@ -5,7 +5,13 @@
 import time
 
 size = 10
-lag = concore.tryparam("lag", 0) 
+lag = concore.tryparam("lag", 0)
+if lag >= size:
+    logging.warning(
+        "Requested lag (%d) exceeds buffer size (%d). Clamping to %d.",
+        lag, size, size - 1
+    )
+    lag = size - 1
 logging.info(f"plot ym with lag={lag}")
 
 concore.delay = 0.005