From 616e506f2e12983d1d5eeb7eca66e32b5aa876d9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Sun, 17 Nov 2019 11:20:59 +0100
Subject: [PATCH] csi: fix bad implementation of CBT (back tab)

* It takes a parameter, that indicates the number of tab stops to move
  through
* Use the tab stops defined in the tab stops list, not hard coded mod
  8 columns.
---
 csi.c | 19 +++++++++++++------
 vt.c  |  1 +
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/csi.c b/csi.c
index a0c909cc..74e68513 100644
--- a/csi.c
+++ b/csi.c
@@ -611,13 +611,20 @@ csi_dispatch(struct terminal *term, uint8_t final)
             break;
         }
 
-        case 'Z': {
-            /* Back tab */
-            int col = term->cursor.point.col;
-            col = (col - 8 + 7) / 8 * 8;
-            term_cursor_right(term, col - term->cursor.point.col);
+        case 'Z':
+            /* CBT - Back tab (param is number of tab stops to move back through) */
+            for (int i = 0; i < vt_param_get(term, 0, 1); i++) {
+                int new_col = 0;
+                tll_rforeach(term->tab_stops, it) {
+                    if (it->item < term->cursor.point.col) {
+                        new_col = it->item;
+                        break;
+                    }
+                }
+                assert(term->cursor.point.col >= new_col);
+                term_cursor_left(term, term->cursor.point.col - new_col);
+            }
             break;
-        }
 
         case 'h':
             /* Set mode */
diff --git a/vt.c b/vt.c
index cad4cbcf..bcce4052 100644
--- a/vt.c
+++ b/vt.c
@@ -875,6 +875,7 @@ action(struct terminal *term, enum action _action, uint8_t c)
                     break;
                 }
             }
+            assert(new_col >= term->cursor.point.col);
             term_cursor_right(term, new_col - term->cursor.point.col);
             break;
         }