vi: remember cursor column during vertical motion

When the 'j'/'k' commands or up/down arrow keys are used to move
the cursor vertically 'vi' remembers the original cursor column
and positions the cursor there if possible.  Also, if the '$'
command has been used to position the cursor at the end of a line
vertical movements keep the cursor at the end of the line.

Make BusyBox 'vi' do the same.

function                                             old     new   delta
refresh                                              674     694     +20
do_cmd                                              4853    4861      +8
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 28/0)               Total: 28 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 18 insertions, 3 deletions

diff --git a/editors/vi.c b/editors/vi.c
index f4da38071..2c724a448 100644
--- a/editors/vi.c
+++ b/editors/vi.c
@@ -263,6 +263,8 @@ enum {
         S_OVER_WS = 3,          // used in skip_thing() for moving "dot"
         S_END_PUNCT = 4,        // used in skip_thing() for moving "dot"
         S_END_ALNUM = 5,        // used in skip_thing() for moving "dot"
+
+        C_END = -1,     // cursor is at end of line due to '$' command
 };
 
 
@@ -354,6 +356,8 @@ struct globals {
         sigjmp_buf restart;     // int_handler() jumps to location remembered here
 #endif
         struct termios term_orig; // remember what the cooked mode was
+        int cindex;               // saved character index for up/down motion
+        smallint keep_index;      // retain saved character index
 #if ENABLE_FEATURE_VI_COLON
         char *initial_cmds[3];  // currently 2 entries, NULL terminated
 #endif
@@ -462,6 +466,8 @@ struct globals {
 #define context_end    (G.context_end   )
 #define restart        (G.restart       )
 #define term_orig      (G.term_orig     )
+#define cindex         (G.cindex        )
+#define keep_index     (G.keep_index    )
 #define initial_cmds   (G.initial_cmds  )
 #define readbuffer     (G.readbuffer    )
 #define scr_out_buf    (G.scr_out_buf   )
@@ -992,6 +998,9 @@ static void refresh(int full_screen)
 
         place_cursor(crow, ccol);
 
+        if (!keep_index)
+                cindex = ccol + offset;
+
         old_offset = offset;
 #undef old_offset
 }
@@ -3096,6 +3105,7 @@ static void do_cmd(int c)
 //      cnt = yf = 0; // quiet the compiler
 //      p = q = save_dot = buf; // quiet the compiler
         memset(buf, '\0', sizeof(buf));
+        keep_index = FALSE;
 
         show_status_line();
 
@@ -3220,9 +3230,10 @@ static void do_cmd(int c)
         case KEYCODE_DOWN:      // cursor key Down
                 do {
                         dot_next();             // go to next B-o-l
-                        // try stay in same col
-                        dot = move_to_col(dot, ccol + offset);
                 } while (--cmdcnt > 0);
+                // try to stay in saved column
+                dot = cindex == C_END ? end_line(dot) : move_to_col(dot, cindex);
+                keep_index = TRUE;
                 break;
         case 12:                        // ctrl-L  force redraw whole screen
         case 18:                        // ctrl-R  force redraw
@@ -3348,6 +3359,8 @@ static void do_cmd(int c)
                                 break;
                         dot_next();
                 }
+                cindex = C_END;
+                keep_index = TRUE;
                 break;
         case '%':                       // %- find matching char of pair () [] {}
                 for (q = dot; q < end && *q != '\n'; q++) {
@@ -3827,8 +3840,10 @@ static void do_cmd(int c)
         case KEYCODE_UP:                // cursor key Up
                 do {
                         dot_prev();
-                        dot = move_to_col(dot, ccol + offset);  // try stay in same col
                 } while (--cmdcnt > 0);
+                // try to stay in saved column
+                dot = cindex == C_END ? end_line(dot) : move_to_col(dot, cindex);
+                keep_index = TRUE;
                 break;
         case 'r':                       // r- replace the current char with user input
                 c1 = get_one_char();    // get the replacement char