[gtksourceview/gnome-3-18] gutterrendererlines: don't use division to calculate number of digits

[Paolo Borelli <pborelli src gnome org>]

commit 28654def54832563bec7c8158cf6ef4a20c8e2f8
Author: Christian Hergert <christian hergert me>
Date:   Wed Apr 20 18:34:44 2016 -0700

    gutterrendererlines: don't use division to calculate number of digits
    
    Avoid looping division to count digits. Not huge gains or anything, but
    common to avoid loop+division in general. ~25% faster for numbers into
    1000s.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=765356

 gtksourceview/gtksourcegutterrendererlines.c |   40 +++++++++++++++++++------
 1 files changed, 30 insertions(+), 10 deletions(-)
---
diff --git a/gtksourceview/gtksourcegutterrendererlines.c b/gtksourceview/gtksourcegutterrendererlines.c
index 578b5a4..c53faa1 100644
--- a/gtksourceview/gtksourcegutterrendererlines.c
+++ b/gtksourceview/gtksourcegutterrendererlines.c
@@ -40,27 +40,47 @@ get_buffer (GtkSourceGutterRendererLines *renderer)
        return view != NULL ? gtk_text_view_get_buffer (view) : NULL;
 }
 
+static inline gint
+count_num_digits (gint num_lines)
+{
+       if (num_lines < 100)
+       {
+               return 2;
+       }
+       else if (num_lines < 1000)
+       {
+               return 3;
+       }
+       else if (num_lines < 10000)
+       {
+               return 4;
+       }
+       else if (num_lines < 100000)
+       {
+               return 5;
+       }
+       else if (num_lines < 1000000)
+       {
+               return 6;
+       }
+       else
+       {
+               return 10;
+       }
+}
+
 static void
 recalculate_size (GtkSourceGutterRendererLines *renderer)
 {
        gint num_lines;
        gint num_digits = 0;
-       gint num;
        GtkTextBuffer *buffer;
 
        buffer = get_buffer (renderer);
 
        num_lines = gtk_text_buffer_get_line_count (buffer);
 
-       num = num_lines;
-
-       while (num > 0)
-       {
-               num /= 10;
-               ++num_digits;
-       }
-
-       num_digits = MAX (num_digits, 2);
+       num_digits = count_num_digits (num_lines);
 
        if (num_digits != renderer->priv->num_line_digits)
        {