text: /*
   * Copyright © 2011,2012  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-ot-shape-complex-indic-private.hh"
  #include "hb-ot-layout-private.hh"
  
  /* buffer var allocations */
  #define khmer_category() complex_var_u8_0() /* khmer_category_t */
  #define khmer_position() complex_var_u8_1() /* khmer_position_t */
  
  
  /*
   * Khmer shaper.
   */
  
  typedef indic_category_t khmer_category_t;
  typedef indic_position_t khmer_position_t;
  
  
  static inline khmer_position_t
  matra_position (khmer_position_t side)
  {
    switch ((int) side)
    {
      case POS_PRE_C:
        return POS_PRE_M;
  
      case POS_POST_C:
      case POS_ABOVE_C:
      case POS_BELOW_C:
        return POS_AFTER_POST;
  
      default:
        return side;
    };
  }
  
  static inline bool
  is_one_of (const hb_glyph_info_t &info, unsigned int flags)
  {
    /* If it ligated, all bets are off. */
    if (_hb_glyph_info_ligated (&info)) return false;
    return !!(FLAG_UNSAFE (info.khmer_category()) & flags);
  }
  
  static inline bool
  is_joiner (const hb_glyph_info_t &info)
  {
    return is_one_of (info, JOINER_FLAGS);
  }
  
  static inline bool
  is_consonant (const hb_glyph_info_t &info)
  {
    return is_one_of (info, CONSONANT_FLAGS | FLAG (OT_V));
  }
  
  static inline bool
  is_coeng (const hb_glyph_info_t &info)
  {
    return is_one_of (info, FLAG (OT_Coeng));
  }
  
  static inline void
  set_khmer_properties (hb_glyph_info_t &info)
  {
    hb_codepoint_t u = info.codepoint;
    unsigned int type = hb_indic_get_categories (u);
    khmer_category_t cat = (khmer_category_t) (type & 0x7Fu);
    khmer_position_t pos = (khmer_position_t) (type >> 8);
  
  
    /*
     * Re-assign category
     */
  
    if (unlikely (u == 0x17C6u)) cat = OT_N; /* Khmer Bindu doesn't like to be repositioned. */
    else if (unlikely (hb_in_range<hb_codepoint_t> (u, 0x17CDu, 0x17D1u) ||
  		     u == 0x17CBu || u == 0x17D3u || u == 0x17DDu)) /* Khmer Various signs */
    {
      /* These can occur mid-syllable (eg. before matras), even though Unicode marks them as Syllable_Modifier.
       * https://github.com/roozbehp/unicode-data/issues/5 */
      cat = OT_M;
      pos = POS_ABOVE_C;
    }
    else if (unlikely (hb_in_range<hb_codepoint_t> (u, 0x2010u, 0x2011u))) cat = OT_PLACEHOLDER;
    else if (unlikely (u == 0x25CCu)) cat = OT_DOTTEDCIRCLE;
  
  
    /*
     * Re-assign position.
     */
  
    if ((FLAG_UNSAFE (cat) & CONSONANT_FLAGS))
    {
      pos = POS_BASE_C;
      if (u == 0x179Au)
        cat = OT_Ra;
    }
    else if (cat == OT_M)
    {
      pos = matra_position (pos);
    }
    else if ((FLAG_UNSAFE (cat) & (FLAG (OT_SM) | FLAG (OT_A) | FLAG (OT_Symbol))))
    {
      pos = POS_SMVD;
    }
  
    info.khmer_category() = cat;
    info.khmer_position() = pos;
  }
  
  /*
   * Things above this line should ideally be moved to the Indic table itself.
   */
  
  
  /*
   * Khmer shaper.
   */
  
  struct feature_list_t {
    hb_tag_t tag;
    hb_ot_map_feature_flags_t flags;
  };
  
  static const feature_list_t
  khmer_features[] =
  {
    /*
     * Basic features.
     * These features are applied in order, one at a time, after initial_reordering.
     */
    {HB_TAG('p','r','e','f'), F_NONE},
    {HB_TAG('b','l','w','f'), F_NONE},
    {HB_TAG('a','b','v','f'), F_NONE},
    {HB_TAG('p','s','t','f'), F_NONE},
    {HB_TAG('c','f','a','r'), F_NONE},
    /*
     * Other features.
     * These features are applied all at once, after final_reordering.
     * Default Bengali font in Windows for example has intermixed
     * lookups for init,pres,abvs,blws features.
     */
    {HB_TAG('p','r','e','s'), F_GLOBAL},
    {HB_TAG('a','b','v','s'), F_GLOBAL},
    {HB_TAG('b','l','w','s'), F_GLOBAL},
    {HB_TAG('p','s','t','s'), F_GLOBAL},
    /* Positioning features, though we don't care about the types. */
    {HB_TAG('d','i','s','t'), F_GLOBAL},
    {HB_TAG('a','b','v','m'), F_GLOBAL},
    {HB_TAG('b','l','w','m'), F_GLOBAL},
  };
  
  /*
   * Must be in the same order as the khmer_features array.
   */
  enum {
    PREF,
    BLWF,
    ABVF,
    PSTF,
    CFAR,
  
    _PRES,
    _ABVS,
    _BLWS,
    _PSTS,
    _DIST,
    _ABVM,
    _BLWM,
  
    KHMER_NUM_FEATURES,
    KHMER_BASIC_FEATURES = _PRES /* Don't forget to update this! */
  };
  
  static void
  setup_syllables (const hb_ot_shape_plan_t *plan,
  		 hb_font_t *font,
  		 hb_buffer_t *buffer);
  static void
  initial_reordering (const hb_ot_shape_plan_t *plan,
  		    hb_font_t *font,
  		    hb_buffer_t *buffer);
  static void
  final_reordering (const hb_ot_shape_plan_t *plan,
  		  hb_font_t *font,
  		  hb_buffer_t *buffer);
  static void
  clear_syllables (const hb_ot_shape_plan_t *plan,
  		 hb_font_t *font,
  		 hb_buffer_t *buffer);
  
  static void
  collect_features_khmer (hb_ot_shape_planner_t *plan)
  {
    hb_ot_map_builder_t *map = &plan->map;
  
    /* Do this before any lookups have been applied. */
    map->add_gsub_pause (setup_syllables);
  
    map->add_global_bool_feature (HB_TAG('l','o','c','l'));
    /* The Indic specs do not require ccmp, but we apply it here since if
     * there is a use of it, it's typically at the beginning. */
    map->add_global_bool_feature (HB_TAG('c','c','m','p'));
  
  
    unsigned int i = 0;
    map->add_gsub_pause (initial_reordering);
    for (; i < KHMER_BASIC_FEATURES; i++) {
      map->add_feature (khmer_features[i].tag, 1, khmer_features[i].flags | F_MANUAL_ZWJ | F_MANUAL_ZWNJ);
      map->add_gsub_pause (nullptr);
    }
    map->add_gsub_pause (final_reordering);
    for (; i < KHMER_NUM_FEATURES; i++) {
      map->add_feature (khmer_features[i].tag, 1, khmer_features[i].flags | F_MANUAL_ZWJ | F_MANUAL_ZWNJ);
    }
  
    map->add_global_bool_feature (HB_TAG('c','a','l','t'));
    map->add_global_bool_feature (HB_TAG('c','l','i','g'));
  
    map->add_gsub_pause (clear_syllables);
  }
  
  static void
  override_features_khmer (hb_ot_shape_planner_t *plan)
  {
    /* Uniscribe does not apply 'kern' in Khmer. */
    if (hb_options ().uniscribe_bug_compatible)
    {
      plan->map.add_feature (HB_TAG('k','e','r','n'), 0, F_GLOBAL);
    }
  
    plan->map.add_feature (HB_TAG('l','i','g','a'), 0, F_GLOBAL);
  }
  
  
  struct would_substitute_feature_t
  {
    inline void init (const hb_ot_map_t *map, hb_tag_t feature_tag, bool zero_context_)
    {
      zero_context = zero_context_;
      map->get_stage_lookups (0/*GSUB*/,
  			    map->get_feature_stage (0/*GSUB*/, feature_tag),
  			    &lookups, &count);
    }
  
    inline bool would_substitute (const hb_codepoint_t *glyphs,
  				unsigned int          glyphs_count,
  				hb_face_t            *face) const
    {
      for (unsigned int i = 0; i < count; i++)
        if (hb_ot_layout_lookup_would_substitute_fast (face, lookups[i].index, glyphs, glyphs_count, zero_context))
  	return true;
      return false;
    }
  
    private:
    const hb_ot_map_t::lookup_map_t *lookups;
    unsigned int count;
    bool zero_context;
  };
  
  struct khmer_shape_plan_t
  {
    ASSERT_POD ();
  
    inline bool get_virama_glyph (hb_font_t *font, hb_codepoint_t *pglyph) const
    {
      hb_codepoint_t glyph = virama_glyph;
      if (unlikely (virama_glyph == (hb_codepoint_t) -1))
      {
        if (!font->get_nominal_glyph (0x17D2u, &glyph))
  	glyph = 0;
        /* Technically speaking, the spec says we should apply 'locl' to virama too.
         * Maybe one day... */
  
        /* Our get_nominal_glyph() function needs a font, so we can't get the virama glyph
         * during shape planning...  Instead, overwrite it here.  It's safe.  Don't worry! */
        virama_glyph = glyph;
      }
  
      *pglyph = glyph;
      return glyph != 0;
    }
  
    mutable hb_codepoint_t virama_glyph;
  
    would_substitute_feature_t pref;
  
    hb_mask_t mask_array[KHMER_NUM_FEATURES];
  };
  
  static void *
  data_create_khmer (const hb_ot_shape_plan_t *plan)
  {
    khmer_shape_plan_t *khmer_plan = (khmer_shape_plan_t *) calloc (1, sizeof (khmer_shape_plan_t));
    if (unlikely (!khmer_plan))
      return nullptr;
  
    khmer_plan->virama_glyph = (hb_codepoint_t) -1;
  
    khmer_plan->pref.init (&plan->map, HB_TAG('p','r','e','f'), true);
  
    for (unsigned int i = 0; i < ARRAY_LENGTH (khmer_plan->mask_array); i++)
      khmer_plan->mask_array[i] = (khmer_features[i].flags & F_GLOBAL) ?
  				 0 : plan->map.get_1_mask (khmer_features[i].tag);
  
    return khmer_plan;
  }
  
  static void
  data_destroy_khmer (void *data)
  {
    free (data);
  }
  
  
  enum syllable_type_t {
    consonant_syllable,
    broken_cluster,
    non_khmer_cluster,
  };
  
  #include "hb-ot-shape-complex-khmer-machine.hh"
  
  static void
  setup_masks_khmer (const hb_ot_shape_plan_t *plan HB_UNUSED,
  		   hb_buffer_t              *buffer,
  		   hb_font_t                *font HB_UNUSED)
  {
    HB_BUFFER_ALLOCATE_VAR (buffer, khmer_category);
    HB_BUFFER_ALLOCATE_VAR (buffer, khmer_position);
  
    /* We cannot setup masks here.  We save information about characters
     * and setup masks later on in a pause-callback. */
  
    unsigned int count = buffer->len;
    hb_glyph_info_t *info = buffer->info;
    for (unsigned int i = 0; i < count; i++)
      set_khmer_properties (info[i]);
  }
  
  static void
  setup_syllables (const hb_ot_shape_plan_t *plan HB_UNUSED,
  		 hb_font_t *font HB_UNUSED,
  		 hb_buffer_t *buffer)
  {
    find_syllables (buffer);
    foreach_syllable (buffer, start, end)
      buffer->unsafe_to_break (start, end);
  }
  
  static int
  compare_khmer_order (const hb_glyph_info_t *pa, const hb_glyph_info_t *pb)
  {
    int a = pa->khmer_position();
    int b = pb->khmer_position();
  
    return a < b ? -1 : a == b ? 0 : +1;
  }
  
  
  /* Rules from:
   * https://www.microsoft.com/typography/otfntdev/devanot/shaping.aspx */
  
  static void
  initial_reordering_consonant_syllable (const hb_ot_shape_plan_t *plan,
  				       hb_face_t *face,
  				       hb_buffer_t *buffer,
  				       unsigned int start, unsigned int end)
  {
    const khmer_shape_plan_t *khmer_plan = (const khmer_shape_plan_t *) plan->data;
    hb_glyph_info_t *info = buffer->info;
  
    /* 1. Khmer shaping assumes that a syllable will begin with a Cons, IndV, or Number. */
  
    /* The first consonant is always the base. */
    unsigned int base = start;
    info[base].khmer_position() = POS_BASE_C;
  
    /* Mark all subsequent consonants as below. */
    for (unsigned int i = base + 1; i < end; i++)
      if (is_consonant (info[i]))
        info[i].khmer_position() = POS_BELOW_C;
  
    /* Mark final consonants.  A final consonant is one appearing after a matra,
     * like in Khmer. */
    for (unsigned int i = base + 1; i < end; i++)
      if (info[i].khmer_category() == OT_M) {
        for (unsigned int j = i + 1; j < end; j++)
          if (is_consonant (info[j])) {
  	  info[j].khmer_position() = POS_FINAL_C;
  	  break;
  	}
        break;
      }
  
    /* Attach misc marks to previous char to move with them. */
    {
      khmer_position_t last_pos = POS_START;
      for (unsigned int i = start; i < end; i++)
      {
        if ((FLAG_UNSAFE (info[i].khmer_category()) & (JOINER_FLAGS | FLAG (OT_N) | FLAG (OT_RS) | MEDIAL_FLAGS | FLAG (OT_Coeng))))
        {
  	info[i].khmer_position() = last_pos;
  	if (unlikely (info[i].khmer_category() == OT_H &&
  		      info[i].khmer_position() == POS_PRE_M))
  	{
  	  /*
  	   * Uniscribe doesn't move the Halant with Left Matra.
  	   * TEST: U+092B,U+093F,U+094DE
  	   * We follow.  This is important for the Sinhala
  	   * U+0DDA split matra since it decomposes to U+0DD9,U+0DCA
  	   * where U+0DD9 is a left matra and U+0DCA is the virama.
  	   * We don't want to move the virama with the left matra.
  	   * TEST: U+0D9A,U+0DDA
  	   */
  	  for (unsigned int j = i; j > start; j--)
  	    if (info[j - 1].khmer_position() != POS_PRE_M) {
  	      info[i].khmer_position() = info[j - 1].khmer_position();
  	      break;
  	    }
  	}
        } else if (info[i].khmer_position() != POS_SMVD) {
          last_pos = (khmer_position_t) info[i].khmer_position();
        }
      }
    }
    /* For post-base consonants let them own anything before them
     * since the last consonant or matra. */
    {
      unsigned int last = base;
      for (unsigned int i = base + 1; i < end; i++)
        if (is_consonant (info[i]))
        {
  	for (unsigned int j = last + 1; j < i; j++)
  	  if (info[j].khmer_position() < POS_SMVD)
  	    info[j].khmer_position() = info[i].khmer_position();
  	last = i;
        } else if (info[i].khmer_category() == OT_M)
          last = i;
    }
  
    {
      /* Use syllable() for sort accounting temporarily. */
      unsigned int syllable = info[start].syllable();
      for (unsigned int i = start; i < end; i++)
        info[i].syllable() = i - start;
  
      /* Sit tight, rock 'n roll! */
      hb_stable_sort (info + start, end - start, compare_khmer_order);
      /* Find base again */
      base = end;
      for (unsigned int i = start; i < end; i++)
        if (info[i].khmer_position() == POS_BASE_C)
        {
  	base = i;
  	break;
        }
  
      /* Note!  syllable() is a one-byte field. */
      for (unsigned int i = base; i < end; i++)
        if (info[i].syllable() != 255)
        {
  	unsigned int max = i;
  	unsigned int j = start + info[i].syllable();
  	while (j != i)
  	{
  	  max = MAX (max, j);
  	  unsigned int next = start + info[j].syllable();
  	  info[j].syllable() = 255; /* So we don't process j later again. */
  	  j = next;
  	}
  	if (i != max)
  	  buffer->merge_clusters (i, max + 1);
        }
  
      /* Put syllable back in. */
      for (unsigned int i = start; i < end; i++)
        info[i].syllable() = syllable;
    }
  
    /* Setup masks now */
  
    {
      hb_mask_t mask;
  
      /* Post-base */
      mask = khmer_plan->mask_array[BLWF] | khmer_plan->mask_array[ABVF] | khmer_plan->mask_array[PSTF];
      for (unsigned int i = base + 1; i < end; i++)
        info[i].mask  |= mask;
    }
  
    unsigned int pref_len = 2;
    if (khmer_plan->mask_array[PREF] && base + pref_len < end)
    {
      /* Find a Halant,Ra sequence and mark it for pre-base-reordering processing. */
      for (unsigned int i = base + 1; i + pref_len - 1 < end; i++) {
        hb_codepoint_t glyphs[2];
        for (unsigned int j = 0; j < pref_len; j++)
          glyphs[j] = info[i + j].codepoint;
        if (khmer_plan->pref.would_substitute (glyphs, pref_len, face))
        {
  	for (unsigned int j = 0; j < pref_len; j++)
  	  info[i++].mask |= khmer_plan->mask_array[PREF];
  
  	/* Mark the subsequent stuff with 'cfar'.  Used in Khmer.
  	 * Read the feature spec.
  	 * This allows distinguishing the following cases with MS Khmer fonts:
  	 * U+1784,U+17D2,U+179A,U+17D2,U+1782
  	 * U+1784,U+17D2,U+1782,U+17D2,U+179A
  	 */
  	if (khmer_plan->mask_array[CFAR])
  	  for (; i < end; i++)
  	    info[i].mask |= khmer_plan->mask_array[CFAR];
  
  	break;
        }
      }
    }
  }
  
  static void
  initial_reordering_syllable (const hb_ot_shape_plan_t *plan,
  			     hb_face_t *face,
  			     hb_buffer_t *buffer,
  			     unsigned int start, unsigned int end)
  {
    syllable_type_t syllable_type = (syllable_type_t) (buffer->info[start].syllable() & 0x0F);
    switch (syllable_type)
    {
      case broken_cluster: /* We already inserted dotted-circles, so just call the consonant_syllable. */
      case consonant_syllable:
       initial_reordering_consonant_syllable (plan, face, buffer, start, end);
       break;
  
      case non_khmer_cluster:
        break;
    }
  }
  
  static inline void
  insert_dotted_circles (const hb_ot_shape_plan_t *plan HB_UNUSED,
  		       hb_font_t *font,
  		       hb_buffer_t *buffer)
  {
    /* Note: This loop is extra overhead, but should not be measurable. */
    bool has_broken_syllables = false;
    unsigned int count = buffer->len;
    hb_glyph_info_t *info = buffer->info;
    for (unsigned int i = 0; i < count; i++)
      if ((info[i].syllable() & 0x0F) == broken_cluster)
      {
        has_broken_syllables = true;
        break;
      }
    if (likely (!has_broken_syllables))
      return;
  
  
    hb_codepoint_t dottedcircle_glyph;
    if (!font->get_nominal_glyph (0x25CCu, &dottedcircle_glyph))
      return;
  
    hb_glyph_info_t dottedcircle = {0};
    dottedcircle.codepoint = 0x25CCu;
    set_khmer_properties (dottedcircle);
    dottedcircle.codepoint = dottedcircle_glyph;
  
    buffer->clear_output ();
  
    buffer->idx = 0;
    unsigned int last_syllable = 0;
    while (buffer->idx < buffer->len && !buffer->in_error)
    {
      unsigned int syllable = buffer->cur().syllable();
      syllable_type_t syllable_type = (syllable_type_t) (syllable & 0x0F);
      if (unlikely (last_syllable != syllable && syllable_type == broken_cluster))
      {
        last_syllable = syllable;
  
        hb_glyph_info_t ginfo = dottedcircle;
        ginfo.cluster = buffer->cur().cluster;
        ginfo.mask = buffer->cur().mask;
        ginfo.syllable() = buffer->cur().syllable();
        /* TODO Set glyph_props? */
  
        /* Insert dottedcircle after possible Repha. */
        while (buffer->idx < buffer->len && !buffer->in_error &&
  	     last_syllable == buffer->cur().syllable() &&
  	     buffer->cur().khmer_category() == OT_Repha)
          buffer->next_glyph ();
  
        buffer->output_info (ginfo);
      }
      else
        buffer->next_glyph ();
    }
  
    buffer->swap_buffers ();
  }
  
  static void
  initial_reordering (const hb_ot_shape_plan_t *plan,
  		    hb_font_t *font,
  		    hb_buffer_t *buffer)
  {
    insert_dotted_circles (plan, font, buffer);
  
    foreach_syllable (buffer, start, end)
      initial_reordering_syllable (plan, font->face, buffer, start, end);
  }
  
  static void
  final_reordering_syllable (const hb_ot_shape_plan_t *plan,
  			   hb_buffer_t *buffer,
  			   unsigned int start, unsigned int end)
  {
    const khmer_shape_plan_t *khmer_plan = (const khmer_shape_plan_t *) plan->data;
    hb_glyph_info_t *info = buffer->info;
  
  
    /* This function relies heavily on halant glyphs.  Lots of ligation
     * and possibly multiple substitutions happened prior to this
     * phase, and that might have messed up our properties.  Recover
     * from a particular case of that where we're fairly sure that a
     * class of OT_H is desired but has been lost. */
    if (khmer_plan->virama_glyph)
    {
      unsigned int virama_glyph = khmer_plan->virama_glyph;
      for (unsigned int i = start; i < end; i++)
        if (info[i].codepoint == virama_glyph &&
  	  _hb_glyph_info_ligated (&info[i]) &&
  	  _hb_glyph_info_multiplied (&info[i]))
        {
          /* This will make sure that this glyph passes is_coeng() test. */
  	info[i].khmer_category() = OT_H;
  	_hb_glyph_info_clear_ligated_and_multiplied (&info[i]);
        }
    }
  
  
    /* 4. Final reordering:
     *
     * After the localized forms and basic shaping forms GSUB features have been
     * applied (see below), the shaping engine performs some final glyph
     * reordering before applying all the remaining font features to the entire
     * syllable.
     */
  
    bool try_pref = !!khmer_plan->mask_array[PREF];
  
    /* Find base again */
    unsigned int base;
    for (base = start; base < end; base++)
      if (info[base].khmer_position() >= POS_BASE_C)
      {
        if (try_pref && base + 1 < end)
        {
  	for (unsigned int i = base + 1; i < end; i++)
  	  if ((info[i].mask & khmer_plan->mask_array[PREF]) != 0)
  	  {
  	    if (!(_hb_glyph_info_substituted (&info[i]) &&
  		  _hb_glyph_info_ligated_and_didnt_multiply (&info[i])))
  	    {
  	      /* Ok, this was a 'pref' candidate but didn't form any.
  	       * Base is around here... */
  	      base = i;
  	      while (base < end && is_coeng (info[base]))
  		base++;
  	      info[base].khmer_position() = POS_BASE_C;
  
  	      try_pref = false;
  	    }
  	    break;
  	  }
        }
  
        if (start < base && info[base].khmer_position() > POS_BASE_C)
          base--;
        break;
      }
    if (base == end && start < base &&
        is_one_of (info[base - 1], FLAG (OT_ZWJ)))
      base--;
    if (base < end)
      while (start < base &&
  	   is_one_of (info[base], (FLAG (OT_N) | FLAG (OT_Coeng))))
        base--;
  
  
    /*   o Reorder matras:
     *
     *     If a pre-base matra character had been reordered before applying basic
     *     features, the glyph can be moved closer to the main consonant based on
     *     whether half-forms had been formed. Actual position for the matra is
     *     defined as “after last standalone halant glyph, after initial matra
     *     position and before the main consonant”. If ZWJ or ZWNJ follow this
     *     halant, position is moved after it.
     */
  
    if (start + 1 < end && start < base) /* Otherwise there can't be any pre-base matra characters. */
    {
      /* If we lost track of base, alas, position before last thingy. */
      unsigned int new_pos = base == end ? base - 2 : base - 1;
  
      while (new_pos > start &&
  	   !(is_one_of (info[new_pos], (FLAG (OT_M) | FLAG (OT_Coeng)))))
        new_pos--;
  
      /* If we found no Halant we are done.
       * Otherwise only proceed if the Halant does
       * not belong to the Matra itself! */
      if (is_coeng (info[new_pos]) &&
  	info[new_pos].khmer_position() != POS_PRE_M)
      {
        /* -> If ZWJ or ZWNJ follow this halant, position is moved after it. */
        if (new_pos + 1 < end && is_joiner (info[new_pos + 1]))
  	new_pos++;
      }
      else
        new_pos = start; /* No move. */
  
      if (start < new_pos && info[new_pos].khmer_position () != POS_PRE_M)
      {
        /* Now go see if there's actually any matras... */
        for (unsigned int i = new_pos; i > start; i--)
  	if (info[i - 1].khmer_position () == POS_PRE_M)
  	{
  	  unsigned int old_pos = i - 1;
  	  if (old_pos < base && base <= new_pos) /* Shouldn't actually happen. */
  	    base--;
  
  	  hb_glyph_info_t tmp = info[old_pos];
  	  memmove (&info[old_pos], &info[old_pos + 1], (new_pos - old_pos) * sizeof (info[0]));
  	  info[new_pos] = tmp;
  
  	  /* Note: this merge_clusters() is intentionally *after* the reordering.
  	   * Indic matra reordering is special and tricky... */
  	  buffer->merge_clusters (new_pos, MIN (end, base + 1));
  
  	  new_pos--;
  	}
      } else {
        for (unsigned int i = start; i < base; i++)
  	if (info[i].khmer_position () == POS_PRE_M) {
  	  buffer->merge_clusters (i, MIN (end, base + 1));
  	  break;
  	}
      }
    }
  
  
    /*   o Reorder pre-base-reordering consonants:
     *
     *     If a pre-base-reordering consonant is found, reorder it according to
     *     the following rules:
     */
  
    if (try_pref && base + 1 < end) /* Otherwise there can't be any pre-base-reordering Ra. */
    {
      for (unsigned int i = base + 1; i < end; i++)
        if ((info[i].mask & khmer_plan->mask_array[PREF]) != 0)
        {
  	/*       1. Only reorder a glyph produced by substitution during application
  	 *          of the <pref> feature. (Note that a font may shape a Ra consonant with
  	 *          the feature generally but block it in certain contexts.)
  	 */
          /* Note: We just check that something got substituted.  We don't check that
  	 * the <pref> feature actually did it...
  	 *
  	 * Reorder pref only if it ligated. */
  	if (_hb_glyph_info_ligated_and_didnt_multiply (&info[i]))
  	{
  	  /*
  	   *       2. Try to find a target position the same way as for pre-base matra.
  	   *          If it is found, reorder pre-base consonant glyph.
  	   *
  	   *       3. If position is not found, reorder immediately before main
  	   *          consonant.
  	   */
  
  	  unsigned int new_pos = base;
  	  while (new_pos > start &&
  		 !(is_one_of (info[new_pos - 1], FLAG(OT_M) | FLAG (OT_Coeng))))
  	    new_pos--;
  
  	  /* In Khmer coeng model, a H,Ra can go *after* matras.  If it goes after a
  	   * split matra, it should be reordered to *before* the left part of such matra. */
  	  if (new_pos > start && info[new_pos - 1].khmer_category() == OT_M)
  	  {
  	    unsigned int old_pos = i;
  	    for (unsigned int j = base + 1; j < old_pos; j++)
  	      if (info[j].khmer_category() == OT_M)
  	      {
  		new_pos--;
  		break;
  	      }
  	  }
  
  	  if (new_pos > start && is_coeng (info[new_pos - 1]))
  	  {
  	    /* -> If ZWJ or ZWNJ follow this halant, position is moved after it. */
  	    if (new_pos < end && is_joiner (info[new_pos]))
  	      new_pos++;
  	  }
  
  	  {
  	    unsigned int old_pos = i;
  
  	    buffer->merge_clusters (new_pos, old_pos + 1);
  	    hb_glyph_info_t tmp = info[old_pos];
  	    memmove (&info[new_pos + 1], &info[new_pos], (old_pos - new_pos) * sizeof (info[0]));
  	    info[new_pos] = tmp;
  
  	    if (new_pos <= base && base < old_pos)
  	      base++;
  	  }
  	}
  
          break;
        }
    }
  
  
    /*
     * Finish off the clusters and go home!
     */
    if (hb_options ().uniscribe_bug_compatible)
    {
      /* Uniscribe merges the entire syllable into a single cluster... Except for Tamil & Sinhala.
       * This means, half forms are submerged into the main consonant's cluster.
       * This is unnecessary, and makes cursor positioning harder, but that's what
       * Uniscribe does. */
      buffer->merge_clusters (start, end);
    }
  }
  
  
  static void
  final_reordering (const hb_ot_shape_plan_t *plan,
  		  hb_font_t *font HB_UNUSED,
  		  hb_buffer_t *buffer)
  {
    unsigned int count = buffer->len;
    if (unlikely (!count)) return;
  
    foreach_syllable (buffer, start, end)
      final_reordering_syllable (plan, buffer, start, end);
  
    HB_BUFFER_DEALLOCATE_VAR (buffer, khmer_category);
    HB_BUFFER_DEALLOCATE_VAR (buffer, khmer_position);
  }
  
  
  static void
  clear_syllables (const hb_ot_shape_plan_t *plan HB_UNUSED,
  		 hb_font_t *font HB_UNUSED,
  		 hb_buffer_t *buffer)
  {
    hb_glyph_info_t *info = buffer->info;
    unsigned int count = buffer->len;
    for (unsigned int i = 0; i < count; i++)
      info[i].syllable() = 0;
  }
  
  
  static bool
  decompose_khmer (const hb_ot_shape_normalize_context_t *c,
  		 hb_codepoint_t  ab,
  		 hb_codepoint_t *a,
  		 hb_codepoint_t *b)
  {
    switch (ab)
    {
      /*
       * Decompose split matras that don't have Unicode decompositions.
       */
  
      /* Khmer */
      case 0x17BEu  : *a = 0x17C1u; *b= 0x17BEu; return true;
      case 0x17BFu  : *a = 0x17C1u; *b= 0x17BFu; return true;
      case 0x17C0u  : *a = 0x17C1u; *b= 0x17C0u; return true;
      case 0x17C4u  : *a = 0x17C1u; *b= 0x17C4u; return true;
      case 0x17C5u  : *a = 0x17C1u; *b= 0x17C5u; return true;
    }
  
    return (bool) c->unicode->decompose (ab, a, b);
  }
  
  static bool
  compose_khmer (const hb_ot_shape_normalize_context_t *c,
  	       hb_codepoint_t  a,
  	       hb_codepoint_t  b,
  	       hb_codepoint_t *ab)
  {
    /* Avoid recomposing split matras. */
    if (HB_UNICODE_GENERAL_CATEGORY_IS_MARK (c->unicode->general_category (a)))
      return false;
  
    return (bool) c->unicode->compose (a, b, ab);
  }
  
  
  const hb_ot_complex_shaper_t _hb_ot_complex_shaper_khmer =
  {
    collect_features_khmer,
    override_features_khmer,
    data_create_khmer,
    data_destroy_khmer,
    nullptr, /* preprocess_text */
    nullptr, /* postprocess_glyphs */
    HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_DIACRITICS_NO_SHORT_CIRCUIT,
    decompose_khmer,
    compose_khmer,
    setup_masks_khmer,
    nullptr, /* disable_otl */
    nullptr, /* reorder_marks */
    HB_OT_SHAPE_ZERO_WIDTH_MARKS_NONE,
    false, /* fallback_position */
  };
  