patch 9.1.0055: formatting long lines is slow

Problem:  formatting long lines is slow
          (kawaii-Code)
Solution: optimize gq (internal_format) for long
          lines (kawaii-Code)

Implemented two workarounds that significantly reduce
the amount of pointless calls. Ideally the algorithm
would be rewritten not to be n^2, but it's too complicated
with too many corner cases.

closes: #13914

Signed-off-by: kawaii-Code <nia.personal.0@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

diff --git a/src/textformat.c b/src/textformat.c
index 5a52950c5e25cec1ea3477f6f824a74b085c51ec..500e8895c818950f67d6c272ab3c31eb62ce2ecc 100644 (file)
--- a/src/textformat.c
+++ b/src/textformat.c
@@ -90,11 +90,18 @@ internal_format(
        colnr_T end_col;
        int     wcc;                    // counter for whitespace chars
        int     did_do_comment = FALSE;
+       int     first_pass;
 
-       virtcol = get_nolist_virtcol()
-                                  + char2cells(c != NUL ? c : gchar_cursor());
-       if (virtcol <= (colnr_T)textwidth)
-           break;
+       // Cursor is currently at the end of line. No need to format
+       // if line length is less than textwidth (8 * textwidth for
+       // utf safety)
+       if (curwin->w_cursor.col < 8 * textwidth)
+       {
+           virtcol = get_nolist_virtcol()
+               + char2cells(c != NUL ? c : gchar_cursor());
+           if (virtcol <= (colnr_T)textwidth)
+               break;
+       }
 
        if (no_leader)
            do_comments = FALSE;
@@ -144,9 +151,17 @@ internal_format(
        coladvance((colnr_T)textwidth);
        wantcol = curwin->w_cursor.col;
 
-       curwin->w_cursor.col = startcol;
+       // If startcol is large (a long line), formatting takes too much
+       // time. The algorithm is O(n^2), it walks from the end of the
+       // line to textwidth border every time for each line break.
+       //
+       // Ceil to 8 * textwidth to optimize.
+       curwin->w_cursor.col = startcol < 8 * textwidth ? startcol :
+           8 * textwidth;
+
        foundcol = 0;
        skip_pos = 0;
+       first_pass = TRUE;
 
        // Find position to break at.
        // Stop at first entered white when 'formatoptions' has 'v'
@@ -155,8 +170,11 @@ internal_format(
                    || curwin->w_cursor.lnum != Insstart.lnum
                    || curwin->w_cursor.col >= Insstart.col)
        {
-           if (curwin->w_cursor.col == startcol && c != NUL)
+           if (first_pass && c != NUL)
+           {
                cc = c;
+               first_pass = FALSE;
+           }
            else
                cc = gchar_cursor();
            if (WHITECHAR(cc))

diff --git a/src/version.c b/src/version.c
index fe10b9569ab07dd2b6b2202ea0c3fa7d1b609ef3..2a654c1d7560bf9d70a380255dff99c34eae8721 100644 (file)
--- a/src/version.c
+++ b/src/version.c
@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    55,
 /**/
     54,
 /**/