From c3b119ea81a7b6bf01cf8ba064ab9df8f7c92f1e Mon Sep 17 00:00:00 2001
From: CismonX <admin@cismon.net>
Date: Thu, 20 Jul 2023 07:00:14 +0800
Subject: [PATCH] vt: improve handling of HTS

Do not insert existing positions into the tab stop list.

This prevents a performance issue when iterating through
an extremely long tab stop list.

Also corrects the behaviour of CBT.
---
 vt.c | 30 ++++++++++++++++++++++--------
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/vt.c b/vt.c
index 2ee2dbaf..51b69c7e 100644
--- a/vt.c
+++ b/vt.c
@@ -436,6 +436,27 @@ UNITTEST
     xassert(term.vt.private == expected);
 }
 
+static void
+tab_set(struct terminal *term)
+{
+    int col = term->grid->cursor.point.col;
+
+    if (tll_length(term->tab_stops) == 0 || tll_back(term->tab_stops) < col) {
+        tll_push_back(term->tab_stops, col);
+        return;
+    }
+
+    tll_foreach(term->tab_stops, it) {
+        if (it->item < col) {
+            continue;
+        }
+        if (it->item > col) {
+            tll_insert_before(term->tab_stops, it, col);
+        }
+        break;
+    }
+}
+
 static void
 action_esc_dispatch(struct terminal *term, uint8_t final)
 {
@@ -478,14 +499,7 @@ action_esc_dispatch(struct terminal *term, uint8_t final)
             break;
 
         case 'H':
-            tll_foreach(term->tab_stops, it) {
-                if (it->item >= term->grid->cursor.point.col) {
-                    tll_insert_before(term->tab_stops, it, term->grid->cursor.point.col);
-                    break;
-                }
-            }
-
-            tll_push_back(term->tab_stops, term->grid->cursor.point.col);
+            tab_set(term);
             break;
 
         case 'M':