[gspell: 4/5] InlineCheckerTextBuffer: faster check_subregion() implementation

[Sébastien Wilmet <swilmet src gnome org>]

commit 36368aff96c26948fcfae18073d2fd2b4b09a6f0
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Sat Apr 1 19:33:01 2017 +0200

    InlineCheckerTextBuffer: faster check_subregion() implementation
    
    For the same long line of text, check_subregion() has been reduced from
    200ms to less than 10ms!
    
    The _gspell_text_iter_*() functions are very slow.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=776811

 gspell/gspell-inline-checker-text-buffer.c |  164 ++++++++++++++++++++++++++++
 1 files changed, 164 insertions(+), 0 deletions(-)
---
diff --git a/gspell/gspell-inline-checker-text-buffer.c b/gspell/gspell-inline-checker-text-buffer.c
index 235dc2f..acf0e36 100644
--- a/gspell/gspell-inline-checker-text-buffer.c
+++ b/gspell/gspell-inline-checker-text-buffer.c
@@ -160,11 +160,72 @@ adjust_iters (GtkTextIter *start,
        }
 }
 
+/* Free *attrs with g_free() when no longer needed. */
+static void
+get_pango_log_attrs (const gchar   *text,
+                    PangoLogAttr **attrs,
+                    gint          *n_attrs)
+{
+       *n_attrs = g_utf8_strlen (text, -1) + 1;
+       *attrs = g_new0 (PangoLogAttr, *n_attrs);
+
+       pango_get_log_attrs (text,
+                            strlen (text),
+                            -1,
+                            NULL,
+                            *attrs,
+                            *n_attrs);
+
+       _gspell_utils_improve_word_boundaries (text, *attrs, *n_attrs);
+}
+
+static gboolean
+should_apply_tag_to_misspelled_word (GspellInlineCheckerTextBuffer *spell,
+                                    const GtkTextIter             *word_start,
+                                    const GtkTextIter             *word_end)
+{
+       GtkTextIter iter;
+
+       if (spell->no_spell_check_tag == NULL)
+       {
+               return TRUE;
+       }
+
+       if (gtk_text_iter_has_tag (word_start, spell->no_spell_check_tag))
+       {
+               return FALSE;
+       }
+
+       iter = *word_start;
+       if (!gtk_text_iter_forward_to_tag_toggle (&iter, spell->no_spell_check_tag))
+       {
+               return TRUE;
+       }
+
+       return gtk_text_iter_compare (word_end, &iter) <= 0;
+}
+
+/* A first implementation of this function used the _gspell_text_iter_*()
+ * functions in a loop to navigate through words between @start and @end.
+ * But the _gspell_text_iter_*() functions are *slow*. So a new implementation
+ * has been written to reduce the number of calls to GtkTextView functions, and
+ * it's up to 20x faster! (200 ms -> 10 ms).
+ * And there is most probably still room for performance improvements.
+ */
 static void
 check_subregion (GspellInlineCheckerTextBuffer *spell,
                 GtkTextIter                   *start,
                 GtkTextIter                   *end)
 {
+       gchar *text;
+       const gchar *cur_text_pos;
+       const gchar *word_start;
+       gint word_start_char_pos;
+       PangoLogAttr *attrs;
+       gint n_attrs;
+       gint attr_num;
+       gint start_offset;
+
        g_return_if_fail (gtk_text_iter_compare (start, end) <= 0);
 
        adjust_iters (start, end, ADJUST_MODE_STRICTLY_INSIDE_WORD);
@@ -173,6 +234,109 @@ check_subregion (GspellInlineCheckerTextBuffer *spell,
                                    spell->highlight_tag,
                                    start,
                                    end);
+
+       if (spell->spell_checker == NULL ||
+           gspell_checker_get_language (spell->spell_checker) == NULL)
+       {
+               return;
+       }
+
+       text = gtk_text_iter_get_slice (start, end);
+
+       get_pango_log_attrs (text, &attrs, &n_attrs);
+
+       attr_num = 0;
+       cur_text_pos = text;
+       word_start = NULL;
+       word_start_char_pos = 0;
+
+       start_offset = gtk_text_iter_get_offset (start);
+
+       while (attr_num < n_attrs)
+       {
+               PangoLogAttr *cur_attr = &attrs[attr_num];
+
+               if (word_start != NULL &&
+                   cur_attr->is_word_end)
+               {
+                       gint word_byte_length;
+                       gboolean misspelled;
+                       GError *error = NULL;
+
+                       if (cur_text_pos != NULL)
+                       {
+                               word_byte_length = cur_text_pos - word_start;
+                       }
+                       else
+                       {
+                               word_byte_length = -1;
+                       }
+
+                       misspelled = !gspell_checker_check_word (spell->spell_checker,
+                                                                word_start,
+                                                                word_byte_length,
+                                                                &error);
+
+                       if (error != NULL)
+                       {
+                               g_warning ("Inline spell checker: %s", error->message);
+                               g_clear_error (&error);
+                       }
+
+                       if (misspelled)
+                       {
+                               gint word_start_offset;
+                               gint word_end_offset;
+                               GtkTextIter word_start_iter;
+                               GtkTextIter word_end_iter;
+
+                               word_start_offset = start_offset + word_start_char_pos;
+                               word_end_offset = start_offset + attr_num;
+
+                               gtk_text_buffer_get_iter_at_offset (spell->buffer,
+                                                                   &word_start_iter,
+                                                                   word_start_offset);
+
+                               gtk_text_buffer_get_iter_at_offset (spell->buffer,
+                                                                   &word_end_iter,
+                                                                   word_end_offset);
+
+                               if (should_apply_tag_to_misspelled_word (spell, &word_start_iter, 
&word_end_iter))
+                               {
+                                       gtk_text_buffer_apply_tag (spell->buffer,
+                                                                  spell->highlight_tag,
+                                                                  &word_start_iter,
+                                                                  &word_end_iter);
+                               }
+                       }
+
+                       /* Find next word start. */
+                       word_start = NULL;
+               }
+
+               if (word_start == NULL &&
+                   cur_attr->is_word_start)
+               {
+                       word_start = cur_text_pos;
+                       word_start_char_pos = attr_num;
+               }
+
+               if (cur_text_pos == NULL &&
+                   attr_num != n_attrs - 1)
+               {
+                       g_warning ("%s(): problem in loop iteration, attr_num=%d but should be %d.",
+                                  G_STRFUNC,
+                                  attr_num,
+                                  n_attrs - 1);
+                       break;
+               }
+
+               attr_num++;
+               cur_text_pos = g_utf8_find_next_char (cur_text_pos, NULL);
+       }
+
+       g_free (text);
+       g_free (attrs);
 }
 
 static void