Speed up redisplay of binary files with long series of nulls

* src/bidi.c (bidi_resolve_weak): Avoid entering a loop searching
for a character needed for resolving the type of a series of BN
and ET characters, as required by rule W5 of UAX#9, if the results
of the resolution are known in advance, because we are at level
zero, and the previous strong character was L.
(bidi_resolve_neutral): Partially resurrect the optimization for a
long series of control characters in an otherwise strictly L2R
text.
(bidi_level_of_next_char): Don't enter the loop that searches for
a paragraph separator if the current character is already at base
embedding level.  (Bug#22739)

1 files changed, 34 insertions, 6 deletions

diff --git a/src/bidi.c b/src/bidi.c
index e7787054e23..9797517e420 100644
--- a/src/bidi.c
+++ b/src/bidi.c
@@ -2318,7 +2318,31 @@ bidi_resolve_weak (struct bidi_it *bidi_it)
               if (bidi_it->next_en_type == WEAK_EN) /* ET/BN with EN after it */
                 type = WEAK_EN;
             }
-          else if (bidi_it->next_en_pos >=0)
+          else if (type == WEAK_BN
+                   /* This condition is for the following important case:
+
+                      . we are at level zero
+                      . either previous strong character was L,
+                         or we've seen no strong characters since sos
+                         and the base paragraph direction is L2R
+                      . this BN is NOT a bidi directional control
+
+                      For such a situation, either this BN will be
+                      converted to EN per W5, and then to L by virtue
+                      of W7; or it will become ON per W6, and then L
+                      because of N1/N2.  So we take a shortcut here
+                      and make it L right away, to avoid the
+                      potentially costly loop below.  This is
+                      important when the buffer has a long series of
+                      control characters, like binary nulls, and no
+                      R2L characters at all.  */
+                   && new_level == 0
+                   && !bidi_explicit_dir_char (bidi_it->ch)
+                   && ((bidi_it->last_strong.type == STRONG_L)
+                       || (bidi_it->last_strong.type == UNKNOWN_BT
+                           && bidi_it->sos == L2R)))
+            type = STRONG_L;
+          else if (bidi_it->next_en_pos >= 0)
             {
               /* We overstepped the last known position for ET
                  resolution but there could be other such characters
@@ -2981,9 +3005,10 @@ bidi_resolve_neutral (struct bidi_it *bidi_it)
          entering the expensive loop in the "else" clause.  */
       else if (current_level == 0
                && bidi_it->prev_for_neutral.type == STRONG_L
-               && type != WEAK_BN
-               && !bidi_explicit_dir_char (bidi_it->ch)
-               && !bidi_isolate_fmt_char (type))
+               && (ASCII_CHAR_P (bidi_it->ch)
+                   || (type != WEAK_BN
+                       && !bidi_explicit_dir_char (bidi_it->ch)
+                       && !bidi_isolate_fmt_char (type))))
         type = bidi_resolve_neutral_1 (bidi_it->prev_for_neutral.type,
                                        STRONG_L, current_level);
       else if (/* current level is 1 */
@@ -3163,7 +3188,7 @@ bidi_level_of_next_char (struct bidi_it *bidi_it)
         }
     }
 
-  /* Perhaps the character we want is already cached s fully resolved.
+  /* Perhaps the character we want is already cached as fully resolved.
      If it is, the call to bidi_cache_find below will return a type
      other than UNKNOWN_BT.  */
   if (bidi_cache_idx > bidi_cache_start && !bidi_it->first_elt)
@@ -3223,7 +3248,10 @@ bidi_level_of_next_char (struct bidi_it *bidi_it)
   if ((bidi_it->orig_type == NEUTRAL_WS
        || bidi_it->orig_type == WEAK_BN
        || bidi_isolate_fmt_char (bidi_it->orig_type))
-      && bidi_it->next_for_ws.charpos < bidi_it->charpos)
+      && bidi_it->next_for_ws.charpos < bidi_it->charpos
+      /* If this character is already at base level, we don't need to
+         reset it, so avoid the potentially costly loop below.  */
+      && level != bidi_it->level_stack[0].level)
     {
       int ch;
       ptrdiff_t clen = bidi_it->ch_len;