--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mupdf-source/thirdparty/harfbuzz/src/hb-ot-shaper-arabic.cc	Mon Sep 15 11:43:07 2025 +0200
@@ -0,0 +1,755 @@
+/*
+ * Copyright © 2010,2012  Google, Inc.
+ *
+ *  This is part of HarfBuzz, a text shaping library.
+ *
+ * Permission is hereby granted, without written agreement and without
+ * license or royalty fees, to use, copy, modify, and distribute this
+ * software and its documentation for any purpose, provided that the
+ * above copyright notice and the following two paragraphs appear in
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ * Google Author(s): Behdad Esfahbod
+ */
+
+#include "hb.hh"
+
+#ifndef HB_NO_OT_SHAPE
+
+#include "hb-ot-shaper-arabic.hh"
+#include "hb-ot-shape.hh"
+
+
+/* buffer var allocations */
+#define arabic_shaping_action() ot_shaper_var_u8_auxiliary() /* arabic shaping action */
+
+#define HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH HB_BUFFER_SCRATCH_FLAG_SHAPER0
+
+/* 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 hb_arabic_joining_type_t {
+  JOINING_TYPE_U		= 0,
+  JOINING_TYPE_L		= 1,
+  JOINING_TYPE_R		= 2,
+  JOINING_TYPE_D		= 3,
+  JOINING_TYPE_C		= JOINING_TYPE_D,
+  JOINING_GROUP_ALAPH		= 4,
+  JOINING_GROUP_DALATH_RISH	= 5,
+  NUM_STATE_MACHINE_COLS	= 6,
+
+  JOINING_TYPE_T = 7,
+  JOINING_TYPE_X = 8  /* means: use general-category to choose between U or T. */
+};
+
+#include "hb-ot-shaper-arabic-table.hh"
+
+static unsigned int get_joining_type (hb_codepoint_t u, hb_unicode_general_category_t gen_cat)
+{
+  unsigned int j_type = joining_type(u);
+  if (likely (j_type != JOINING_TYPE_X))
+    return j_type;
+
+  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))
+	 ) ?  JOINING_TYPE_T : JOINING_TYPE_U;
+}
+
+#define FEATURE_IS_SYRIAC(tag) hb_in_range<unsigned char> ((unsigned char) (tag), '2', '3')
+
+static const hb_tag_t arabic_features[] =
+{
+  HB_TAG('i','s','o','l'),
+  HB_TAG('f','i','n','a'),
+  HB_TAG('f','i','n','2'),
+  HB_TAG('f','i','n','3'),
+  HB_TAG('m','e','d','i'),
+  HB_TAG('m','e','d','2'),
+  HB_TAG('i','n','i','t'),
+  HB_TAG_NONE
+};
+
+
+/* Same order as the feature array */
+enum arabic_action_t {
+  ISOL,
+  FINA,
+  FIN2,
+  FIN3,
+  MEDI,
+  MED2,
+  INIT,
+
+  NONE,
+
+  ARABIC_NUM_FEATURES = NONE,
+
+  /* We abuse the same byte for other things... */
+  STCH_FIXED,
+  STCH_REPEATING,
+};
+
+static const struct arabic_state_table_entry {
+	uint8_t prev_action;
+	uint8_t curr_action;
+	uint16_t next_state;
+} arabic_state_table[][NUM_STATE_MACHINE_COLS] =
+{
+  /*   jt_U,          jt_L,          jt_R,          jt_D,          jg_ALAPH,      jg_DALATH_RISH */
+
+  /* State 0: prev was U, not willing to join. */
+  { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,6}, },
+
+  /* State 1: prev was R or ISOL/ALAPH, not willing to join. */
+  { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,FIN2,5}, {NONE,ISOL,6}, },
+
+  /* State 2: prev was D/L in ISOL form, willing to join. */
+  { {NONE,NONE,0}, {NONE,ISOL,2}, {INIT,FINA,1}, {INIT,FINA,3}, {INIT,FINA,4}, {INIT,FINA,6}, },
+
+  /* State 3: prev was D in FINA form, willing to join. */
+  { {NONE,NONE,0}, {NONE,ISOL,2}, {MEDI,FINA,1}, {MEDI,FINA,3}, {MEDI,FINA,4}, {MEDI,FINA,6}, },
+
+  /* State 4: prev was FINA ALAPH, not willing to join. */
+  { {NONE,NONE,0}, {NONE,ISOL,2}, {MED2,ISOL,1}, {MED2,ISOL,2}, {MED2,FIN2,5}, {MED2,ISOL,6}, },
+
+  /* State 5: prev was FIN2/FIN3 ALAPH, not willing to join. */
+  { {NONE,NONE,0}, {NONE,ISOL,2}, {ISOL,ISOL,1}, {ISOL,ISOL,2}, {ISOL,FIN2,5}, {ISOL,ISOL,6}, },
+
+  /* State 6: prev was DALATH/RISH, not willing to join. */
+  { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,FIN3,5}, {NONE,ISOL,6}, }
+};
+
+
+static bool
+arabic_fallback_shape (const hb_ot_shape_plan_t *plan,
+		       hb_font_t *font,
+		       hb_buffer_t *buffer);
+
+static bool
+record_stch (const hb_ot_shape_plan_t *plan,
+	     hb_font_t *font,
+	     hb_buffer_t *buffer);
+
+static bool
+deallocate_buffer_var (const hb_ot_shape_plan_t *plan,
+		       hb_font_t *font,
+		       hb_buffer_t *buffer)
+{
+  HB_BUFFER_DEALLOCATE_VAR (buffer, arabic_shaping_action);
+  return false;
+}
+
+static void
+collect_features_arabic (hb_ot_shape_planner_t *plan)
+{
+  hb_ot_map_builder_t *map = &plan->map;
+
+  /* We apply features according to the Arabic spec, with pauses
+   * in between most.
+   *
+   * The pause between init/medi/... and rlig is required.  See eg:
+   * https://bugzilla.mozilla.org/show_bug.cgi?id=644184
+   *
+   * The pauses between init/medi/... themselves are not necessarily
+   * needed as only one of those features is applied to any character.
+   * The only difference it makes is when fonts have contextual
+   * substitutions.  We now follow the order of the spec, which makes
+   * for better experience if that's what Uniscribe is doing.
+   *
+   * At least for Arabic, looks like Uniscribe has a pause between
+   * rlig and calt.  Otherwise the IranNastaliq's ALLAH ligature won't
+   * 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.
+   */
+
+
+  map->enable_feature (HB_TAG('s','t','c','h'));
+  map->add_gsub_pause (record_stch);
+
+  map->enable_feature (HB_TAG('c','c','m','p'), F_MANUAL_ZWJ);
+  map->enable_feature (HB_TAG('l','o','c','l'), F_MANUAL_ZWJ);
+
+  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], F_MANUAL_ZWJ | (has_fallback ? F_HAS_FALLBACK : F_NONE));
+    map->add_gsub_pause (nullptr);
+  }
+   map->add_gsub_pause (deallocate_buffer_var);
+
+  /* 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->enable_feature (HB_TAG('c','a','l','t'), F_MANUAL_ZWJ);
+   /* https://github.com/harfbuzz/harfbuzz/issues/1573 */
+   if (!map->has_feature (HB_TAG('r','c','l','t')))
+   {
+     map->add_gsub_pause (nullptr);
+     map->enable_feature (HB_TAG('r','c','l','t'), F_MANUAL_ZWJ);
+   }
+
+   map->enable_feature (HB_TAG('l','i','g','a'), F_MANUAL_ZWJ);
+   map->enable_feature (HB_TAG('c','l','i','g'), F_MANUAL_ZWJ);
+
+  /* The spec includes 'cswh'.  Earlier versions of Windows
+   * used to enable this by default, but testing suggests
+   * that Windows 8 and later do not enable it by default,
+   * and spec now says 'Off by default'.
+   * We disabled this in ae23c24c32.
+   * Note that IranNastaliq uses this feature extensively
+   * to fixup broken glyph sequences.  Oh well...
+   * Test case: U+0643,U+0640,U+0631. */
+  //map->enable_feature (HB_TAG('c','s','w','h'), F_MANUAL_ZWJ);
+  map->enable_feature (HB_TAG('m','s','e','t'), F_MANUAL_ZWJ);
+}
+
+#include "hb-ot-shaper-arabic-fallback.hh"
+
+struct arabic_shape_plan_t
+{
+  /* 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];
+
+  hb_atomic_ptr_t<arabic_fallback_plan_t> fallback_plan;
+
+  unsigned int do_fallback : 1;
+  unsigned int has_stch : 1;
+};
+
+void *
+data_create_arabic (const hb_ot_shape_plan_t *plan)
+{
+  arabic_shape_plan_t *arabic_plan = (arabic_shape_plan_t *) hb_calloc (1, sizeof (arabic_shape_plan_t));
+  if (unlikely (!arabic_plan))
+    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 &&
+			       (FEATURE_IS_SYRIAC (arabic_features[i]) ||
+				plan->map.needs_fallback (arabic_features[i]));
+  }
+
+  return arabic_plan;
+}
+
+void
+data_destroy_arabic (void *data)
+{
+  arabic_shape_plan_t *arabic_plan = (arabic_shape_plan_t *) data;
+
+  arabic_fallback_plan_destroy (arabic_plan->fallback_plan);
+
+  hb_free (data);
+}
+
+static void
+arabic_joining (hb_buffer_t *buffer)
+{
+  unsigned int count = buffer->len;
+  hb_glyph_info_t *info = buffer->info;
+  unsigned int prev = UINT_MAX, state = 0;
+
+  /* Check pre-context */
+  for (unsigned int i = 0; i < buffer->context_len[0]; i++)
+  {
+    unsigned int this_type = get_joining_type (buffer->context[0][i], buffer->unicode->general_category (buffer->context[0][i]));
+
+    if (unlikely (this_type == JOINING_TYPE_T))
+      continue;
+
+    const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
+    state = entry->next_state;
+    break;
+  }
+
+  for (unsigned int i = 0; i < count; i++)
+  {
+    unsigned int this_type = get_joining_type (info[i].codepoint, _hb_glyph_info_get_general_category (&info[i]));
+
+    if (unlikely (this_type == JOINING_TYPE_T)) {
+      info[i].arabic_shaping_action() = NONE;
+      continue;
+    }
+
+    const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
+
+    if (entry->prev_action != NONE && prev != UINT_MAX)
+    {
+      info[prev].arabic_shaping_action() = entry->prev_action;
+      buffer->safe_to_insert_tatweel (prev, i + 1);
+    }
+    else
+    {
+      if (prev == UINT_MAX)
+      {
+        if (this_type >= JOINING_TYPE_R)
+	  buffer->unsafe_to_concat_from_outbuffer (0, i + 1);
+      }
+      else
+      {
+	if (this_type >= JOINING_TYPE_R ||
+	    (2 <= state && state <= 5) /* States that have a possible prev_action. */)
+	  buffer->unsafe_to_concat (prev, i + 1);
+      }
+    }
+
+    info[i].arabic_shaping_action() = entry->curr_action;
+
+    prev = i;
+    state = entry->next_state;
+  }
+
+  for (unsigned int i = 0; i < buffer->context_len[1]; i++)
+  {
+    unsigned int this_type = get_joining_type (buffer->context[1][i], buffer->unicode->general_category (buffer->context[1][i]));
+
+    if (unlikely (this_type == JOINING_TYPE_T))
+      continue;
+
+    const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
+    if (entry->prev_action != NONE && prev != UINT_MAX)
+    {
+      info[prev].arabic_shaping_action() = entry->prev_action;
+      buffer->safe_to_insert_tatweel (prev, buffer->len);
+    }
+    else if (2 <= state && state <= 5) /* States that have a possible prev_action. */
+    {
+      buffer->unsafe_to_concat (prev, buffer->len);
+    }
+    break;
+  }
+}
+
+static void
+mongolian_variation_selectors (hb_buffer_t *buffer)
+{
+  /* Copy arabic_shaping_action() from base to Mongolian variation selectors. */
+  unsigned int count = buffer->len;
+  hb_glyph_info_t *info = buffer->info;
+  for (unsigned int i = 1; i < count; i++)
+    if (unlikely (hb_in_ranges<hb_codepoint_t> (info[i].codepoint, 0x180Bu, 0x180Du, 0x180Fu, 0x180Fu)))
+      info[i].arabic_shaping_action() = info[i - 1].arabic_shaping_action();
+}
+
+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);
+
+  arabic_joining (buffer);
+  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()];
+}
+
+static void
+setup_masks_arabic (const hb_ot_shape_plan_t *plan,
+		    hb_buffer_t              *buffer,
+		    hb_font_t                *font HB_UNUSED)
+{
+  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 bool
+arabic_fallback_shape (const hb_ot_shape_plan_t *plan,
+		       hb_font_t *font,
+		       hb_buffer_t *buffer)
+{
+#ifdef HB_NO_OT_SHAPER_ARABIC_FALLBACK
+  return false;
+#endif
+
+  const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
+
+  if (!arabic_plan->do_fallback)
+    return false;
+
+retry:
+  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 (!arabic_plan->fallback_plan.cmpexch (nullptr, fallback_plan)))
+    {
+      arabic_fallback_plan_destroy (fallback_plan);
+      goto retry;
+    }
+  }
+
+  arabic_fallback_plan_shape (fallback_plan, font, buffer);
+  return true;
+}
+
+/*
+ * 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 bool
+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 false;
+
+  /* '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;
+    }
+  return false;
+}
+
+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);
+}
+
+/* https://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 */
+  0x08CAu, /* ARABIC SMALL HIGH FARSI YEH */
+  0x08CBu, /* ARABIC SMALL HIGH YEH BARREE WITH TWO DOTS BELOW */
+  0x08CDu, /* ARABIC SMALL HIGH ZAH */
+  0x08CEu, /* ARABIC LARGE ROUND DOT ABOVE */
+  0x08CFu, /* ARABIC LARGE ROUND DOT BELOW */
+  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_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_shaper_t _hb_ot_shaper_arabic =
+{
+  collect_features_arabic,
+  nullptr, /* override_features */
+  data_create_arabic,
+  data_destroy_arabic,
+  nullptr, /* preprocess_text */
+  postprocess_glyphs_arabic,
+  nullptr, /* decompose */
+  nullptr, /* compose */
+  setup_masks_arabic,
+  reorder_marks_arabic,
+  HB_TAG_NONE, /* gpos_tag */
+  HB_OT_SHAPE_NORMALIZATION_MODE_DEFAULT,
+  HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
+  true, /* fallback_position */
+};
+
+
+#endif