Imported Upstream version 2.4.0
[platform/upstream/harfbuzz.git] / src / hb-ot-shape-complex-arabic.cc
index ae90864..bdebde0 100644 (file)
  * Google Author(s): Behdad Esfahbod
  */
 
-#include "hb-ot-shape-complex-private.hh"
-#include "hb-ot-shape-private.hh"
+#include "hb.hh"
+#include "hb-ot-shape-complex-arabic.hh"
+#include "hb-ot-shape.hh"
 
 
 /* buffer var allocations */
 #define arabic_shaping_action() complex_var_u8_0() /* arabic shaping action */
 
+#define HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH HB_BUFFER_SCRATCH_FLAG_COMPLEX0
+
+/* See:
+ * https://github.com/harfbuzz/harfbuzz/commit/6e6f82b6f3dde0fc6c3c7d991d9ec6cfff57823d#commitcomment-14248516 */
+#define HB_ARABIC_GENERAL_CATEGORY_IS_WORD(gen_cat) \
+       (FLAG_UNSAFE (gen_cat) & \
+        (FLAG (HB_UNICODE_GENERAL_CATEGORY_UNASSIGNED) | \
+         FLAG (HB_UNICODE_GENERAL_CATEGORY_PRIVATE_USE) | \
+         /*FLAG (HB_UNICODE_GENERAL_CATEGORY_LOWERCASE_LETTER) |*/ \
+         FLAG (HB_UNICODE_GENERAL_CATEGORY_MODIFIER_LETTER) | \
+         FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_LETTER) | \
+         /*FLAG (HB_UNICODE_GENERAL_CATEGORY_TITLECASE_LETTER) |*/ \
+         /*FLAG (HB_UNICODE_GENERAL_CATEGORY_UPPERCASE_LETTER) |*/ \
+         FLAG (HB_UNICODE_GENERAL_CATEGORY_SPACING_MARK) | \
+         FLAG (HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) | \
+         FLAG (HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) | \
+         FLAG (HB_UNICODE_GENERAL_CATEGORY_DECIMAL_NUMBER) | \
+         FLAG (HB_UNICODE_GENERAL_CATEGORY_LETTER_NUMBER) | \
+         FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_NUMBER) | \
+         FLAG (HB_UNICODE_GENERAL_CATEGORY_CURRENCY_SYMBOL) | \
+         FLAG (HB_UNICODE_GENERAL_CATEGORY_MODIFIER_SYMBOL) | \
+         FLAG (HB_UNICODE_GENERAL_CATEGORY_MATH_SYMBOL) | \
+         FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_SYMBOL)))
+
+
+/*
+ * Joining types:
+ */
 
 /*
  * Bits used in the joining tables
  */
-enum {
+enum hb_arabic_joining_type_t {
   JOINING_TYPE_U               = 0,
   JOINING_TYPE_L               = 1,
   JOINING_TYPE_R               = 2,
@@ -49,10 +78,6 @@ enum {
   JOINING_TYPE_X = 8  /* means: use general-category to choose between U or T. */
 };
 
-/*
- * Joining types:
- */
-
 #include "hb-ot-shape-complex-arabic-table.hh"
 
 static unsigned int get_joining_type (hb_codepoint_t u, hb_unicode_general_category_t gen_cat)
@@ -61,7 +86,7 @@ static unsigned int get_joining_type (hb_codepoint_t u, hb_unicode_general_categ
   if (likely (j_type != JOINING_TYPE_X))
     return j_type;
 
-  return (FLAG(gen_cat) &
+  return (FLAG_UNSAFE(gen_cat) &
          (FLAG(HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) |
           FLAG(HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) |
           FLAG(HB_UNICODE_GENERAL_CATEGORY_FORMAT))
@@ -84,7 +109,7 @@ static const hb_tag_t arabic_features[] =
 
 
 /* Same order as the feature array */
-enum {
+enum arabic_action_t {
   ISOL,
   FINA,
   FIN2,
@@ -95,7 +120,11 @@ enum {
 
   NONE,
 
-  ARABIC_NUM_FEATURES = NONE
+  ARABIC_NUM_FEATURES = NONE,
+
+  /* We abuse the same byte for other things... */
+  STCH_FIXED,
+  STCH_REPEATING,
 };
 
 static const struct arabic_state_table_entry {
@@ -130,16 +159,16 @@ static const struct arabic_state_table_entry {
 
 
 static void
-nuke_joiners (const hb_ot_shape_plan_t *plan,
-             hb_font_t *font,
-             hb_buffer_t *buffer);
-
-static void
 arabic_fallback_shape (const hb_ot_shape_plan_t *plan,
                       hb_font_t *font,
                       hb_buffer_t *buffer);
 
 static void
+record_stch (const hb_ot_shape_plan_t *plan,
+            hb_font_t *font,
+            hb_buffer_t *buffer);
+
+static void
 collect_features_arabic (hb_ot_shape_planner_t *plan)
 {
   hb_ot_map_builder_t *map = &plan->map;
@@ -161,28 +190,42 @@ collect_features_arabic (hb_ot_shape_planner_t *plan)
    * work.  However, testing shows that rlig and calt are applied
    * together for Mongolian in Uniscribe.  As such, we only add a
    * pause for Arabic, not other scripts.
+   *
+   * A pause after calt is required to make KFGQPC Uthmanic Script HAFS
+   * work correctly.  See https://github.com/harfbuzz/harfbuzz/issues/505
    */
 
-  map->add_gsub_pause (nuke_joiners);
 
-  map->add_global_bool_feature (HB_TAG('c','c','m','p'));
-  map->add_global_bool_feature (HB_TAG('l','o','c','l'));
+  map->enable_feature (HB_TAG('s','t','c','h'));
+  map->add_gsub_pause (record_stch);
 
-  map->add_gsub_pause (NULL);
+  map->enable_feature (HB_TAG('c','c','m','p'));
+  map->enable_feature (HB_TAG('l','o','c','l'));
+
+  map->add_gsub_pause (nullptr);
 
   for (unsigned int i = 0; i < ARABIC_NUM_FEATURES; i++)
   {
     bool has_fallback = plan->props.script == HB_SCRIPT_ARABIC && !FEATURE_IS_SYRIAC (arabic_features[i]);
-    map->add_feature (arabic_features[i], 1, has_fallback ? F_HAS_FALLBACK : F_NONE);
-    map->add_gsub_pause (NULL);
+    map->add_feature (arabic_features[i], has_fallback ? F_HAS_FALLBACK : F_NONE);
+    map->add_gsub_pause (nullptr);
   }
 
-  map->add_feature (HB_TAG('r','l','i','g'), 1, F_GLOBAL|F_HAS_FALLBACK);
+  /* Normally, Unicode says a ZWNJ means "don't ligate".  In Arabic script
+   * however, it says a ZWJ should also mean "don't ligate".  So we run
+   * the main ligating features as MANUAL_ZWJ. */
+
+  map->enable_feature (HB_TAG('r','l','i','g'), F_MANUAL_ZWJ | F_HAS_FALLBACK);
+
   if (plan->props.script == HB_SCRIPT_ARABIC)
     map->add_gsub_pause (arabic_fallback_shape);
 
-  map->add_global_bool_feature (HB_TAG('c','a','l','t'));
-  map->add_gsub_pause (NULL);
+  /* No pause after rclt.  See 98460779bae19e4d64d29461ff154b3527bf8420. */
+  map->enable_feature (HB_TAG('r','c','l','t'), F_MANUAL_ZWJ);
+  map->enable_feature (HB_TAG('c','a','l','t'), F_MANUAL_ZWJ);
+  map->add_gsub_pause (nullptr);
+
+  /* And undo here. */
 
   /* The spec includes 'cswh'.  Earlier versions of Windows
    * used to enable this by default, but testing suggests
@@ -192,34 +235,35 @@ collect_features_arabic (hb_ot_shape_planner_t *plan)
    * Note that IranNastaliq uses this feature extensively
    * to fixup broken glyph sequences.  Oh well...
    * Test case: U+0643,U+0640,U+0631. */
-  //map->add_global_bool_feature (HB_TAG('c','s','w','h'));
-  map->add_global_bool_feature (HB_TAG('m','s','e','t'));
+  //map->enable_feature (HB_TAG('c','s','w','h'));
+  map->enable_feature (HB_TAG('m','s','e','t'));
 }
 
 #include "hb-ot-shape-complex-arabic-fallback.hh"
 
 struct arabic_shape_plan_t
 {
-  ASSERT_POD ();
-
   /* The "+ 1" in the next array is to accommodate for the "NONE" command,
    * which is not an OpenType feature, but this simplifies the code by not
    * having to do a "if (... < NONE) ..." and just rely on the fact that
    * mask_array[NONE] == 0. */
   hb_mask_t mask_array[ARABIC_NUM_FEATURES + 1];
 
-  bool do_fallback;
-  arabic_fallback_plan_t *fallback_plan;
+  hb_atomic_ptr_t<arabic_fallback_plan_t> fallback_plan;
+
+  unsigned int do_fallback : 1;
+  unsigned int has_stch : 1;
 };
 
-static void *
+void *
 data_create_arabic (const hb_ot_shape_plan_t *plan)
 {
   arabic_shape_plan_t *arabic_plan = (arabic_shape_plan_t *) calloc (1, sizeof (arabic_shape_plan_t));
   if (unlikely (!arabic_plan))
-    return NULL;
+    return nullptr;
 
   arabic_plan->do_fallback = plan->props.script == HB_SCRIPT_ARABIC;
+  arabic_plan->has_stch = !!plan->map.get_1_mask (HB_TAG ('s','t','c','h'));
   for (unsigned int i = 0; i < ARABIC_NUM_FEATURES; i++) {
     arabic_plan->mask_array[i] = plan->map.get_1_mask (arabic_features[i]);
     arabic_plan->do_fallback = arabic_plan->do_fallback &&
@@ -230,7 +274,7 @@ data_create_arabic (const hb_ot_shape_plan_t *plan)
   return arabic_plan;
 }
 
-static void
+void
 data_destroy_arabic (void *data)
 {
   arabic_shape_plan_t *arabic_plan = (arabic_shape_plan_t *) data;
@@ -272,7 +316,10 @@ arabic_joining (hb_buffer_t *buffer)
     const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
 
     if (entry->prev_action != NONE && prev != (unsigned int) -1)
+    {
       info[prev].arabic_shaping_action() = entry->prev_action;
+      buffer->unsafe_to_break (prev, i + 1);
+    }
 
     info[i].arabic_shaping_action() = entry->curr_action;
 
@@ -301,42 +348,34 @@ mongolian_variation_selectors (hb_buffer_t *buffer)
   unsigned int count = buffer->len;
   hb_glyph_info_t *info = buffer->info;
   for (unsigned int i = 1; i < count; i++)
-    if (unlikely (hb_in_range (info[i].codepoint, 0x180Bu, 0x180Du)))
+    if (unlikely (hb_in_range<hb_codepoint_t> (info[i].codepoint, 0x180Bu, 0x180Du)))
       info[i].arabic_shaping_action() = info[i - 1].arabic_shaping_action();
 }
 
-static void
-setup_masks_arabic (const hb_ot_shape_plan_t *plan,
-                   hb_buffer_t              *buffer,
-                   hb_font_t                *font HB_UNUSED)
+void
+setup_masks_arabic_plan (const arabic_shape_plan_t *arabic_plan,
+                        hb_buffer_t               *buffer,
+                        hb_script_t                script)
 {
   HB_BUFFER_ALLOCATE_VAR (buffer, arabic_shaping_action);
 
-  const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
-
   arabic_joining (buffer);
-  if (plan->props.script == HB_SCRIPT_MONGOLIAN)
+  if (script == HB_SCRIPT_MONGOLIAN)
     mongolian_variation_selectors (buffer);
 
   unsigned int count = buffer->len;
   hb_glyph_info_t *info = buffer->info;
   for (unsigned int i = 0; i < count; i++)
     info[i].mask |= arabic_plan->mask_array[info[i].arabic_shaping_action()];
-
-  HB_BUFFER_DEALLOCATE_VAR (buffer, arabic_shaping_action);
 }
 
-
 static void
-nuke_joiners (const hb_ot_shape_plan_t *plan HB_UNUSED,
-             hb_font_t *font HB_UNUSED,
-             hb_buffer_t *buffer)
+setup_masks_arabic (const hb_ot_shape_plan_t *plan,
+                   hb_buffer_t              *buffer,
+                   hb_font_t                *font HB_UNUSED)
 {
-  unsigned int count = buffer->len;
-  hb_glyph_info_t *info = buffer->info;
-  for (unsigned int i = 0; i < count; i++)
-    if (_hb_glyph_info_is_zwj (&info[i]))
-      _hb_glyph_info_flip_joiners (&info[i]);
+  const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
+  setup_masks_arabic_plan (arabic_plan, buffer, plan->props.script);
 }
 
 static void
@@ -350,12 +389,13 @@ arabic_fallback_shape (const hb_ot_shape_plan_t *plan,
     return;
 
 retry:
-  arabic_fallback_plan_t *fallback_plan = (arabic_fallback_plan_t *) hb_atomic_ptr_get (&arabic_plan->fallback_plan);
+  arabic_fallback_plan_t *fallback_plan = arabic_plan->fallback_plan;
   if (unlikely (!fallback_plan))
   {
     /* This sucks.  We need a font to build the fallback plan... */
     fallback_plan = arabic_fallback_plan_create (plan, font);
-    if (unlikely (!hb_atomic_ptr_cmpexch (&(const_cast<arabic_shape_plan_t *> (arabic_plan))->fallback_plan, NULL, fallback_plan))) {
+    if (unlikely (!arabic_plan->fallback_plan.cmpexch (nullptr, fallback_plan)))
+    {
       arabic_fallback_plan_destroy (fallback_plan);
       goto retry;
     }
@@ -364,19 +404,305 @@ retry:
   arabic_fallback_plan_shape (fallback_plan, font, buffer);
 }
 
+/*
+ * Stretch feature: "stch".
+ * See example here:
+ * https://docs.microsoft.com/en-us/typography/script-development/syriac
+ * We implement this in a generic way, such that the Arabic subtending
+ * marks can use it as well.
+ */
+
+static void
+record_stch (const hb_ot_shape_plan_t *plan,
+            hb_font_t *font HB_UNUSED,
+            hb_buffer_t *buffer)
+{
+  const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
+  if (!arabic_plan->has_stch)
+    return;
+
+  /* 'stch' feature was just applied.  Look for anything that multiplied,
+   * and record it for stch treatment later.  Note that rtlm, frac, etc
+   * are applied before stch, but we assume that they didn't result in
+   * anything multiplying into 5 pieces, so it's safe-ish... */
+
+  unsigned int count = buffer->len;
+  hb_glyph_info_t *info = buffer->info;
+  for (unsigned int i = 0; i < count; i++)
+    if (unlikely (_hb_glyph_info_multiplied (&info[i])))
+    {
+      unsigned int comp = _hb_glyph_info_get_lig_comp (&info[i]);
+      info[i].arabic_shaping_action() = comp % 2 ? STCH_REPEATING : STCH_FIXED;
+      buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH;
+    }
+}
+
+static void
+apply_stch (const hb_ot_shape_plan_t *plan HB_UNUSED,
+           hb_buffer_t              *buffer,
+           hb_font_t                *font)
+{
+  if (likely (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH)))
+    return;
+
+  /* The Arabic shaper currently always processes in RTL mode, so we should
+   * stretch / position the stretched pieces to the left / preceding glyphs. */
+
+  /* We do a two pass implementation:
+   * First pass calculates the exact number of extra glyphs we need,
+   * We then enlarge buffer to have that much room,
+   * Second pass applies the stretch, copying things to the end of buffer.
+   */
+
+  int sign = font->x_scale < 0 ? -1 : +1;
+  unsigned int extra_glyphs_needed = 0; // Set during MEASURE, used during CUT
+  enum { MEASURE, CUT } /* step_t */;
+
+  for (unsigned int step = MEASURE; step <= CUT; step = step + 1)
+  {
+    unsigned int count = buffer->len;
+    hb_glyph_info_t *info = buffer->info;
+    hb_glyph_position_t *pos = buffer->pos;
+    unsigned int new_len = count + extra_glyphs_needed; // write head during CUT
+    unsigned int j = new_len;
+    for (unsigned int i = count; i; i--)
+    {
+      if (!hb_in_range<uint8_t> (info[i - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING))
+      {
+        if (step == CUT)
+       {
+         --j;
+         info[j] = info[i - 1];
+         pos[j] = pos[i - 1];
+       }
+        continue;
+      }
+
+      /* Yay, justification! */
+
+      hb_position_t w_total = 0; // Total to be filled
+      hb_position_t w_fixed = 0; // Sum of fixed tiles
+      hb_position_t w_repeating = 0; // Sum of repeating tiles
+      int n_fixed = 0;
+      int n_repeating = 0;
+
+      unsigned int end = i;
+      while (i &&
+            hb_in_range<uint8_t> (info[i - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING))
+      {
+       i--;
+       hb_position_t width = font->get_glyph_h_advance (info[i].codepoint);
+       if (info[i].arabic_shaping_action() == STCH_FIXED)
+       {
+         w_fixed += width;
+         n_fixed++;
+       }
+       else
+       {
+         w_repeating += width;
+         n_repeating++;
+       }
+      }
+      unsigned int start = i;
+      unsigned int context = i;
+      while (context &&
+            !hb_in_range<uint8_t> (info[context - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING) &&
+            (_hb_glyph_info_is_default_ignorable (&info[context - 1]) ||
+             HB_ARABIC_GENERAL_CATEGORY_IS_WORD (_hb_glyph_info_get_general_category (&info[context - 1]))))
+      {
+       context--;
+       w_total += pos[context].x_advance;
+      }
+      i++; // Don't touch i again.
+
+      DEBUG_MSG (ARABIC, nullptr, "%s stretch at (%d,%d,%d)",
+                step == MEASURE ? "measuring" : "cutting", context, start, end);
+      DEBUG_MSG (ARABIC, nullptr, "rest of word:    count=%d width %d", start - context, w_total);
+      DEBUG_MSG (ARABIC, nullptr, "fixed tiles:     count=%d width=%d", n_fixed, w_fixed);
+      DEBUG_MSG (ARABIC, nullptr, "repeating tiles: count=%d width=%d", n_repeating, w_repeating);
+
+      /* Number of additional times to repeat each repeating tile. */
+      int n_copies = 0;
+
+      hb_position_t w_remaining = w_total - w_fixed;
+      if (sign * w_remaining > sign * w_repeating && sign * w_repeating > 0)
+       n_copies = (sign * w_remaining) / (sign * w_repeating) - 1;
+
+      /* See if we can improve the fit by adding an extra repeat and squeezing them together a bit. */
+      hb_position_t extra_repeat_overlap = 0;
+      hb_position_t shortfall = sign * w_remaining - sign * w_repeating * (n_copies + 1);
+      if (shortfall > 0 && n_repeating > 0)
+      {
+        ++n_copies;
+        hb_position_t excess = (n_copies + 1) * sign * w_repeating - sign * w_remaining;
+        if (excess > 0)
+          extra_repeat_overlap = excess / (n_copies * n_repeating);
+      }
+
+      if (step == MEASURE)
+      {
+       extra_glyphs_needed += n_copies * n_repeating;
+       DEBUG_MSG (ARABIC, nullptr, "will add extra %d copies of repeating tiles", n_copies);
+      }
+      else
+      {
+       buffer->unsafe_to_break (context, end);
+       hb_position_t x_offset = 0;
+       for (unsigned int k = end; k > start; k--)
+       {
+         hb_position_t width = font->get_glyph_h_advance (info[k - 1].codepoint);
+
+         unsigned int repeat = 1;
+         if (info[k - 1].arabic_shaping_action() == STCH_REPEATING)
+           repeat += n_copies;
+
+         DEBUG_MSG (ARABIC, nullptr, "appending %d copies of glyph %d; j=%d",
+                    repeat, info[k - 1].codepoint, j);
+         for (unsigned int n = 0; n < repeat; n++)
+         {
+           x_offset -= width;
+           if (n > 0)
+             x_offset += extra_repeat_overlap;
+           pos[k - 1].x_offset = x_offset;
+           /* Append copy. */
+           --j;
+           info[j] = info[k - 1];
+           pos[j] = pos[k - 1];
+         }
+       }
+      }
+    }
+
+    if (step == MEASURE)
+    {
+      if (unlikely (!buffer->ensure (count + extra_glyphs_needed)))
+        break;
+    }
+    else
+    {
+      assert (j == 0);
+      buffer->len = new_len;
+    }
+  }
+}
+
+
+static void
+postprocess_glyphs_arabic (const hb_ot_shape_plan_t *plan,
+                          hb_buffer_t              *buffer,
+                          hb_font_t                *font)
+{
+  apply_stch (plan, buffer, font);
+
+  HB_BUFFER_DEALLOCATE_VAR (buffer, arabic_shaping_action);
+}
+
+/* http://www.unicode.org/reports/tr53/ */
+
+static hb_codepoint_t
+modifier_combining_marks[] =
+{
+  0x0654u, /* ARABIC HAMZA ABOVE */
+  0x0655u, /* ARABIC HAMZA BELOW */
+  0x0658u, /* ARABIC MARK NOON GHUNNA */
+  0x06DCu, /* ARABIC SMALL HIGH SEEN */
+  0x06E3u, /* ARABIC SMALL LOW SEEN */
+  0x06E7u, /* ARABIC SMALL HIGH YEH */
+  0x06E8u, /* ARABIC SMALL HIGH NOON */
+  0x08D3u, /* ARABIC SMALL LOW WAW */
+  0x08F3u, /* ARABIC SMALL HIGH WAW */
+};
+
+static inline bool
+info_is_mcm (const hb_glyph_info_t &info)
+{
+  hb_codepoint_t u = info.codepoint;
+  for (unsigned int i = 0; i < ARRAY_LENGTH (modifier_combining_marks); i++)
+    if (u == modifier_combining_marks[i])
+      return true;
+  return false;
+}
+
+static void
+reorder_marks_arabic (const hb_ot_shape_plan_t *plan HB_UNUSED,
+                     hb_buffer_t              *buffer,
+                     unsigned int              start,
+                     unsigned int              end)
+{
+  hb_glyph_info_t *info = buffer->info;
+
+  DEBUG_MSG (ARABIC, buffer, "Reordering marks from %d to %d", start, end);
+
+  unsigned int i = start;
+  for (unsigned int cc = 220; cc <= 230; cc += 10)
+  {
+    DEBUG_MSG (ARABIC, buffer, "Looking for %d's starting at %d", cc, i);
+    while (i < end && info_cc(info[i]) < cc)
+      i++;
+    DEBUG_MSG (ARABIC, buffer, "Looking for %d's stopped at %d", cc, i);
+
+    if (i == end)
+      break;
+
+    if (info_cc(info[i]) > cc)
+      continue;
+
+    unsigned int j = i;
+    while (j < end && info_cc(info[j]) == cc && info_is_mcm (info[j]))
+      j++;
+
+    if (i == j)
+      continue;
+
+    DEBUG_MSG (ARABIC, buffer, "Found %d's from %d to %d", cc, i, j);
+
+    /* Shift it! */
+    DEBUG_MSG (ARABIC, buffer, "Shifting %d's: %d %d", cc, i, j);
+    hb_glyph_info_t temp[HB_OT_SHAPE_COMPLEX_MAX_COMBINING_MARKS];
+    assert (j - i <= ARRAY_LENGTH (temp));
+    buffer->merge_clusters (start, j);
+    memmove (temp, &info[i], (j - i) * sizeof (hb_glyph_info_t));
+    memmove (&info[start + j - i], &info[start], (i - start) * sizeof (hb_glyph_info_t));
+    memmove (&info[start], temp, (j - i) * sizeof (hb_glyph_info_t));
+
+    /* Renumber CC such that the reordered sequence is still sorted.
+     * 22 and 26 are chosen because they are smaller than all Arabic categories,
+     * and are folded back to 220/230 respectively during fallback mark positioning.
+     *
+     * We do this because the CGJ-handling logic in the normalizer relies on
+     * mark sequences having an increasing order even after this reordering.
+     * https://github.com/harfbuzz/harfbuzz/issues/554
+     * This, however, does break some obscure sequences, where the normalizer
+     * might compose a sequence that it should not.  For example, in the seequence
+     * ALEF, HAMZAH, MADDAH, we should NOT try to compose ALEF+MADDAH, but with this
+     * renumbering, we will.
+     */
+    unsigned int new_start = start + j - i;
+    unsigned int new_cc = cc == 220 ? HB_MODIFIED_COMBINING_CLASS_CCC22 : HB_MODIFIED_COMBINING_CLASS_CCC26;
+    while (start < new_start)
+    {
+      _hb_glyph_info_set_modified_combining_class (&info[start], new_cc);
+      start++;
+    }
+
+    i = j;
+  }
+}
 
 const hb_ot_complex_shaper_t _hb_ot_complex_shaper_arabic =
 {
-  "arabic",
   collect_features_arabic,
-  NULL, /* override_features */
+  nullptr, /* override_features */
   data_create_arabic,
   data_destroy_arabic,
-  NULL, /* preprocess_text_arabic */
+  nullptr, /* preprocess_text */
+  postprocess_glyphs_arabic,
   HB_OT_SHAPE_NORMALIZATION_MODE_DEFAULT,
-  NULL, /* decompose */
-  NULL, /* compose */
+  nullptr, /* decompose */
+  nullptr, /* compose */
   setup_masks_arabic,
+  HB_TAG_NONE, /* gpos_tag */
+  reorder_marks_arabic,
   HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
   true, /* fallback_position */
 };