Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1578 insertions, 0 deletions

diff --git a/gfx/harfbuzz/src/hb-ot-shaper-indic.cc b/gfx/harfbuzz/src/hb-ot-shaper-indic.cc
new file mode 100644
index 0000000000..f8c970fc3e
--- /dev/null
+++ b/gfx/harfbuzz/src/hb-ot-shaper-indic.cc
@@ -0,0 +1,1578 @@
+/*
+ * 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.hh"
+
+#ifndef HB_NO_OT_SHAPE
+
+#include "hb-ot-shaper-indic.hh"
+#include "hb-ot-shaper-indic-machine.hh"
+#include "hb-ot-shaper-vowel-constraints.hh"
+#include "hb-ot-layout.hh"
+
+
+/*
+ * Indic shaper.
+ */
+
+
+static inline void
+set_indic_properties (hb_glyph_info_t &info)
+{
+  hb_codepoint_t u = info.codepoint;
+  unsigned int type = hb_indic_get_categories (u);
+
+  info.indic_category() = (indic_category_t) (type & 0xFFu);
+  info.indic_position() = (indic_position_t) (type >> 8);
+}
+
+
+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.indic_category()) & flags);
+}
+
+/* Note:
+ *
+ * We treat Vowels and placeholders as if they were consonants.  This is safe because Vowels
+ * cannot happen in a consonant syllable.  The plus side however is, we can call the
+ * consonant syllable logic from the vowel syllable function and get it all right!
+ *
+ * Keep in sync with consonant_categories in the generator. */
+#define CONSONANT_FLAGS_INDIC (FLAG (I_Cat(C)) | FLAG (I_Cat(CS)) | FLAG (I_Cat(Ra)) | FLAG (I_Cat(CM)) | FLAG (I_Cat(V)) | FLAG (I_Cat(PLACEHOLDER)) | FLAG (I_Cat(DOTTEDCIRCLE)))
+
+static inline bool
+is_consonant (const hb_glyph_info_t &info)
+{
+  return is_one_of (info, CONSONANT_FLAGS_INDIC);
+}
+
+#define JOINER_FLAGS (FLAG (I_Cat(ZWJ)) | FLAG (I_Cat(ZWNJ)))
+
+static inline bool
+is_joiner (const hb_glyph_info_t &info)
+{
+  return is_one_of (info, JOINER_FLAGS);
+}
+
+static inline bool
+is_halant (const hb_glyph_info_t &info)
+{
+  return is_one_of (info, FLAG (I_Cat(H)));
+}
+
+struct hb_indic_would_substitute_feature_t
+{
+  void init (const hb_ot_map_t *map, hb_tag_t feature_tag, bool zero_context_)
+  {
+    zero_context = zero_context_;
+    lookups = map->get_stage_lookups (0/*GSUB*/,
+				      map->get_feature_stage (0/*GSUB*/, feature_tag));
+  }
+
+  bool would_substitute (const hb_codepoint_t *glyphs,
+			 unsigned int          glyphs_count,
+			 hb_face_t            *face) const
+  {
+    for (const auto &lookup : lookups)
+      if (hb_ot_layout_lookup_would_substitute (face, lookup.index, glyphs, glyphs_count, zero_context))
+	return true;
+    return false;
+  }
+
+  private:
+  hb_array_t<const hb_ot_map_t::lookup_map_t> lookups;
+  bool zero_context;
+};
+
+
+/*
+ * Indic configurations.  Note that we do not want to keep every single script-specific
+ * behavior in these tables necessarily.  This should mainly be used for per-script
+ * properties that are cheaper keeping here, than in the code.  Ie. if, say, one and
+ * only one script has an exception, that one script can be if'ed directly in the code,
+ * instead of adding a new flag in these structs.
+ */
+
+enum reph_position_t {
+  REPH_POS_AFTER_MAIN  = POS_AFTER_MAIN,
+  REPH_POS_BEFORE_SUB  = POS_BEFORE_SUB,
+  REPH_POS_AFTER_SUB   = POS_AFTER_SUB,
+  REPH_POS_BEFORE_POST = POS_BEFORE_POST,
+  REPH_POS_AFTER_POST  = POS_AFTER_POST
+};
+enum reph_mode_t {
+  REPH_MODE_IMPLICIT,  /* Reph formed out of initial Ra,H sequence. */
+  REPH_MODE_EXPLICIT,  /* Reph formed out of initial Ra,H,ZWJ sequence. */
+  REPH_MODE_LOG_REPHA  /* Encoded Repha character, needs reordering. */
+};
+enum blwf_mode_t {
+  BLWF_MODE_PRE_AND_POST, /* Below-forms feature applied to pre-base and post-base. */
+  BLWF_MODE_POST_ONLY     /* Below-forms feature applied to post-base only. */
+};
+struct indic_config_t
+{
+  hb_script_t     script;
+  bool            has_old_spec;
+  hb_codepoint_t  virama;
+  reph_position_t reph_pos;
+  reph_mode_t     reph_mode;
+  blwf_mode_t     blwf_mode;
+};
+
+static const indic_config_t indic_configs[] =
+{
+  /* Default.  Should be first. */
+  {HB_SCRIPT_INVALID,	false,      0,REPH_POS_BEFORE_POST,REPH_MODE_IMPLICIT, BLWF_MODE_PRE_AND_POST},
+  {HB_SCRIPT_DEVANAGARI,true, 0x094Du,REPH_POS_BEFORE_POST,REPH_MODE_IMPLICIT, BLWF_MODE_PRE_AND_POST},
+  {HB_SCRIPT_BENGALI,	true, 0x09CDu,REPH_POS_AFTER_SUB,  REPH_MODE_IMPLICIT, BLWF_MODE_PRE_AND_POST},
+  {HB_SCRIPT_GURMUKHI,	true, 0x0A4Du,REPH_POS_BEFORE_SUB, REPH_MODE_IMPLICIT, BLWF_MODE_PRE_AND_POST},
+  {HB_SCRIPT_GUJARATI,	true, 0x0ACDu,REPH_POS_BEFORE_POST,REPH_MODE_IMPLICIT, BLWF_MODE_PRE_AND_POST},
+  {HB_SCRIPT_ORIYA,	true, 0x0B4Du,REPH_POS_AFTER_MAIN, REPH_MODE_IMPLICIT, BLWF_MODE_PRE_AND_POST},
+  {HB_SCRIPT_TAMIL,	true, 0x0BCDu,REPH_POS_AFTER_POST, REPH_MODE_IMPLICIT, BLWF_MODE_PRE_AND_POST},
+  {HB_SCRIPT_TELUGU,	true, 0x0C4Du,REPH_POS_AFTER_POST, REPH_MODE_EXPLICIT, BLWF_MODE_POST_ONLY},
+  {HB_SCRIPT_KANNADA,	true, 0x0CCDu,REPH_POS_AFTER_POST, REPH_MODE_IMPLICIT, BLWF_MODE_POST_ONLY},
+  {HB_SCRIPT_MALAYALAM,	true, 0x0D4Du,REPH_POS_AFTER_MAIN, REPH_MODE_LOG_REPHA,BLWF_MODE_PRE_AND_POST},
+};
+
+
+static const hb_ot_map_feature_t
+indic_features[] =
+{
+  /*
+   * Basic features.
+   * These features are applied in order, one at a time, after initial_reordering,
+   * constrained to the syllable.
+   */
+  {HB_TAG('n','u','k','t'), F_GLOBAL_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('a','k','h','n'), F_GLOBAL_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('r','p','h','f'),        F_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('r','k','r','f'), F_GLOBAL_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('p','r','e','f'),        F_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('b','l','w','f'),        F_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('a','b','v','f'),        F_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('h','a','l','f'),        F_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('p','s','t','f'),        F_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('v','a','t','u'), F_GLOBAL_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('c','j','c','t'), F_GLOBAL_MANUAL_JOINERS | F_PER_SYLLABLE},
+  /*
+   * Other features.
+   * These features are applied all at once, after final_reordering, constrained
+   * to the syllable.
+   * Default Bengali font in Windows for example has intermixed
+   * lookups for init,pres,abvs,blws features.
+   */
+  {HB_TAG('i','n','i','t'),        F_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('p','r','e','s'), F_GLOBAL_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('a','b','v','s'), F_GLOBAL_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('b','l','w','s'), F_GLOBAL_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('p','s','t','s'), F_GLOBAL_MANUAL_JOINERS | F_PER_SYLLABLE},
+  {HB_TAG('h','a','l','n'), F_GLOBAL_MANUAL_JOINERS | F_PER_SYLLABLE},
+};
+
+/*
+ * Must be in the same order as the indic_features array.
+ */
+enum {
+  _INDIC_NUKT,
+  _INDIC_AKHN,
+  INDIC_RPHF,
+  _INDIC_RKRF,
+  INDIC_PREF,
+  INDIC_BLWF,
+  INDIC_ABVF,
+  INDIC_HALF,
+  INDIC_PSTF,
+  _INDIC_VATU,
+  _INDIC_CJCT,
+
+  INDIC_INIT,
+  _INDIC_PRES,
+  _INDIC_ABVS,
+  _INDIC_BLWS,
+  _INDIC_PSTS,
+  _INDIC_HALN,
+
+  INDIC_NUM_FEATURES,
+  INDIC_BASIC_FEATURES = INDIC_INIT, /* Don't forget to update this! */
+};
+
+static bool
+setup_syllables_indic (const hb_ot_shape_plan_t *plan,
+		       hb_font_t *font,
+		       hb_buffer_t *buffer);
+static bool
+initial_reordering_indic (const hb_ot_shape_plan_t *plan,
+			  hb_font_t *font,
+			  hb_buffer_t *buffer);
+static bool
+final_reordering_indic (const hb_ot_shape_plan_t *plan,
+			hb_font_t *font,
+			hb_buffer_t *buffer);
+
+static void
+collect_features_indic (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_indic);
+
+  map->enable_feature (HB_TAG('l','o','c','l'), F_PER_SYLLABLE);
+  /* 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->enable_feature (HB_TAG('c','c','m','p'), F_PER_SYLLABLE);
+
+
+  unsigned int i = 0;
+  map->add_gsub_pause (initial_reordering_indic);
+
+  for (; i < INDIC_BASIC_FEATURES; i++) {
+    map->add_feature (indic_features[i]);
+    map->add_gsub_pause (nullptr);
+  }
+
+  map->add_gsub_pause (final_reordering_indic);
+
+  for (; i < INDIC_NUM_FEATURES; i++)
+    map->add_feature (indic_features[i]);
+}
+
+static void
+override_features_indic (hb_ot_shape_planner_t *plan)
+{
+  plan->map.disable_feature (HB_TAG('l','i','g','a'));
+  plan->map.add_gsub_pause (hb_syllabic_clear_var); // Don't need syllables anymore, use stop to free buffer var
+}
+
+
+struct indic_shape_plan_t
+{
+  bool load_virama_glyph (hb_font_t *font, hb_codepoint_t *pglyph) const
+  {
+    hb_codepoint_t glyph = virama_glyph;
+    if (unlikely (glyph == (hb_codepoint_t) -1))
+    {
+      if (!config->virama || !font->get_nominal_glyph (config->virama, &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. */
+      virama_glyph = (int) glyph;
+    }
+
+    *pglyph = glyph;
+    return glyph != 0;
+  }
+
+  const indic_config_t *config;
+
+  bool is_old_spec;
+#ifndef HB_NO_UNISCRIBE_BUG_COMPATIBLE
+  bool uniscribe_bug_compatible;
+#else
+  static constexpr bool uniscribe_bug_compatible = false;
+#endif
+  mutable hb_atomic_int_t virama_glyph;
+
+  hb_indic_would_substitute_feature_t rphf;
+  hb_indic_would_substitute_feature_t pref;
+  hb_indic_would_substitute_feature_t blwf;
+  hb_indic_would_substitute_feature_t pstf;
+  hb_indic_would_substitute_feature_t vatu;
+
+  hb_mask_t mask_array[INDIC_NUM_FEATURES];
+};
+
+static void *
+data_create_indic (const hb_ot_shape_plan_t *plan)
+{
+  indic_shape_plan_t *indic_plan = (indic_shape_plan_t *) hb_calloc (1, sizeof (indic_shape_plan_t));
+  if (unlikely (!indic_plan))
+    return nullptr;
+
+  indic_plan->config = &indic_configs[0];
+  for (unsigned int i = 1; i < ARRAY_LENGTH (indic_configs); i++)
+    if (plan->props.script == indic_configs[i].script) {
+      indic_plan->config = &indic_configs[i];
+      break;
+    }
+
+  indic_plan->is_old_spec = indic_plan->config->has_old_spec && ((plan->map.chosen_script[0] & 0x000000FFu) != '2');
+#ifndef HB_NO_UNISCRIBE_BUG_COMPATIBLE
+  indic_plan->uniscribe_bug_compatible = hb_options ().uniscribe_bug_compatible;
+#endif
+  indic_plan->virama_glyph = -1;
+
+  /* Use zero-context would_substitute() matching for new-spec of the main
+   * Indic scripts, and scripts with one spec only, but not for old-specs.
+   * The new-spec for all dual-spec scripts says zero-context matching happens.
+   *
+   * However, testing with Malayalam shows that old and new spec both allow
+   * context.  Testing with Bengali new-spec however shows that it doesn't.
+   * So, the heuristic here is the way it is.  It should *only* be changed,
+   * as we discover more cases of what Windows does.  DON'T TOUCH OTHERWISE.
+   */
+  bool zero_context = !indic_plan->is_old_spec && plan->props.script != HB_SCRIPT_MALAYALAM;
+  indic_plan->rphf.init (&plan->map, HB_TAG('r','p','h','f'), zero_context);
+  indic_plan->pref.init (&plan->map, HB_TAG('p','r','e','f'), zero_context);
+  indic_plan->blwf.init (&plan->map, HB_TAG('b','l','w','f'), zero_context);
+  indic_plan->pstf.init (&plan->map, HB_TAG('p','s','t','f'), zero_context);
+  indic_plan->vatu.init (&plan->map, HB_TAG('v','a','t','u'), zero_context);
+
+  for (unsigned int i = 0; i < ARRAY_LENGTH (indic_plan->mask_array); i++)
+    indic_plan->mask_array[i] = (indic_features[i].flags & F_GLOBAL) ?
+				 0 : plan->map.get_1_mask (indic_features[i].tag);
+
+  return indic_plan;
+}
+
+static void
+data_destroy_indic (void *data)
+{
+  hb_free (data);
+}
+
+static indic_position_t
+consonant_position_from_face (const indic_shape_plan_t *indic_plan,
+			      const hb_codepoint_t consonant,
+			      const hb_codepoint_t virama,
+			      hb_face_t *face)
+{
+  /* For old-spec, the order of glyphs is Consonant,Virama,
+   * whereas for new-spec, it's Virama,Consonant.  However,
+   * some broken fonts (like Free Sans) simply copied lookups
+   * from old-spec to new-spec without modification.
+   * And oddly enough, Uniscribe seems to respect those lookups.
+   * Eg. in the sequence U+0924,U+094D,U+0930, Uniscribe finds
+   * base at 0.  The font however, only has lookups matching
+   * 930,94D in 'blwf', not the expected 94D,930 (with new-spec
+   * table).  As such, we simply match both sequences.  Seems
+   * to work.
+   *
+   * Vatu is done as well, for:
+   * https://github.com/harfbuzz/harfbuzz/issues/1587
+   */
+  hb_codepoint_t glyphs[3] = {virama, consonant, virama};
+  if (indic_plan->blwf.would_substitute (glyphs  , 2, face) ||
+      indic_plan->blwf.would_substitute (glyphs+1, 2, face) ||
+      indic_plan->vatu.would_substitute (glyphs  , 2, face) ||
+      indic_plan->vatu.would_substitute (glyphs+1, 2, face))
+    return POS_BELOW_C;
+  if (indic_plan->pstf.would_substitute (glyphs  , 2, face) ||
+      indic_plan->pstf.would_substitute (glyphs+1, 2, face))
+    return POS_POST_C;
+  if (indic_plan->pref.would_substitute (glyphs  , 2, face) ||
+      indic_plan->pref.would_substitute (glyphs+1, 2, face))
+    return POS_POST_C;
+  return POS_BASE_C;
+}
+
+static void
+setup_masks_indic (const hb_ot_shape_plan_t *plan HB_UNUSED,
+		   hb_buffer_t              *buffer,
+		   hb_font_t                *font HB_UNUSED)
+{
+  HB_BUFFER_ALLOCATE_VAR (buffer, indic_category);
+  HB_BUFFER_ALLOCATE_VAR (buffer, indic_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_indic_properties (info[i]);
+}
+
+static bool
+setup_syllables_indic (const hb_ot_shape_plan_t *plan HB_UNUSED,
+		       hb_font_t *font HB_UNUSED,
+		       hb_buffer_t *buffer)
+{
+  HB_BUFFER_ALLOCATE_VAR (buffer, syllable);
+  find_syllables_indic (buffer);
+  foreach_syllable (buffer, start, end)
+    buffer->unsafe_to_break (start, end);
+  return false;
+}
+
+static int
+compare_indic_order (const hb_glyph_info_t *pa, const hb_glyph_info_t *pb)
+{
+  int a = pa->indic_position();
+  int b = pb->indic_position();
+
+  return (int) a - (int) b;
+}
+
+
+
+static void
+update_consonant_positions_indic (const hb_ot_shape_plan_t *plan,
+				  hb_font_t         *font,
+				  hb_buffer_t       *buffer)
+{
+  const indic_shape_plan_t *indic_plan = (const indic_shape_plan_t *) plan->data;
+
+  hb_codepoint_t virama;
+  if (indic_plan->load_virama_glyph (font, &virama))
+  {
+    hb_face_t *face = font->face;
+    unsigned int count = buffer->len;
+    hb_glyph_info_t *info = buffer->info;
+    for (unsigned int i = 0; i < count; i++)
+      if (info[i].indic_position() == POS_BASE_C)
+      {
+	hb_codepoint_t consonant = info[i].codepoint;
+	info[i].indic_position() = consonant_position_from_face (indic_plan, consonant, virama, face);
+      }
+  }
+}
+
+
+/* Rules from:
+ * https://docs.microsqoft.com/en-us/typography/script-development/devanagari */
+
+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 indic_shape_plan_t *indic_plan = (const indic_shape_plan_t *) plan->data;
+  hb_glyph_info_t *info = buffer->info;
+
+  /* https://github.com/harfbuzz/harfbuzz/issues/435#issuecomment-335560167
+   * // For compatibility with legacy usage in Kannada,
+   * // Ra+h+ZWJ must behave like Ra+ZWJ+h...
+   */
+  if (buffer->props.script == HB_SCRIPT_KANNADA &&
+      start + 3 <= end &&
+      is_one_of (info[start  ], FLAG (I_Cat(Ra))) &&
+      is_one_of (info[start+1], FLAG (I_Cat(H))) &&
+      is_one_of (info[start+2], FLAG (I_Cat(ZWJ))))
+  {
+    buffer->merge_clusters (start+1, start+3);
+    hb_swap (info[start+1], info[start+2]);
+  }
+
+  /* 1. Find base consonant:
+   *
+   * The shaping engine finds the base consonant of the syllable, using the
+   * following algorithm: starting from the end of the syllable, move backwards
+   * until a consonant is found that does not have a below-base or post-base
+   * form (post-base forms have to follow below-base forms), or that is not a
+   * pre-base-reordering Ra, or arrive at the first consonant. The consonant
+   * stopped at will be the base.
+   *
+   *   o If the syllable starts with Ra + Halant (in a script that has Reph)
+   *     and has more than one consonant, Ra is excluded from candidates for
+   *     base consonants.
+   */
+
+  unsigned int base = end;
+  bool has_reph = false;
+
+  {
+    /* -> If the syllable starts with Ra + Halant (in a script that has Reph)
+     *    and has more than one consonant, Ra is excluded from candidates for
+     *    base consonants. */
+    unsigned int limit = start;
+    if (indic_plan->mask_array[INDIC_RPHF] &&
+	start + 3 <= end &&
+	(
+	 (indic_plan->config->reph_mode == REPH_MODE_IMPLICIT && !is_joiner (info[start + 2])) ||
+	 (indic_plan->config->reph_mode == REPH_MODE_EXPLICIT && info[start + 2].indic_category() == I_Cat(ZWJ))
+	))
+    {
+      /* See if it matches the 'rphf' feature. */
+      hb_codepoint_t glyphs[3] = {info[start].codepoint,
+				  info[start + 1].codepoint,
+				  indic_plan->config->reph_mode == REPH_MODE_EXPLICIT ?
+				    info[start + 2].codepoint : 0};
+      if (indic_plan->rphf.would_substitute (glyphs, 2, face) ||
+	  (indic_plan->config->reph_mode == REPH_MODE_EXPLICIT &&
+	   indic_plan->rphf.would_substitute (glyphs, 3, face)))
+      {
+	limit += 2;
+	while (limit < end && is_joiner (info[limit]))
+	  limit++;
+	base = start;
+	has_reph = true;
+      }
+    } else if (indic_plan->config->reph_mode == REPH_MODE_LOG_REPHA && info[start].indic_category() == I_Cat(Repha))
+    {
+	limit += 1;
+	while (limit < end && is_joiner (info[limit]))
+	  limit++;
+	base = start;
+	has_reph = true;
+    }
+
+    {
+      /* -> starting from the end of the syllable, move backwards */
+      unsigned int i = end;
+      bool seen_below = false;
+      do {
+	i--;
+	/* -> until a consonant is found */
+	if (is_consonant (info[i]))
+	{
+	  /* -> that does not have a below-base or post-base form
+	   * (post-base forms have to follow below-base forms), */
+	  if (info[i].indic_position() != POS_BELOW_C &&
+	      (info[i].indic_position() != POS_POST_C || seen_below))
+	  {
+	    base = i;
+	    break;
+	  }
+	  if (info[i].indic_position() == POS_BELOW_C)
+	    seen_below = true;
+
+	  /* -> or that is not a pre-base-reordering Ra,
+	   *
+	   * IMPLEMENTATION NOTES:
+	   *
+	   * Our pre-base-reordering Ra's are marked POS_POST_C, so will be skipped
+	   * by the logic above already.
+	   */
+
+	  /* -> or arrive at the first consonant. The consonant stopped at will
+	   * be the base. */
+	  base = i;
+	}
+	else
+	{
+	  /* A ZWJ after a Halant stops the base search, and requests an explicit
+	   * half form.
+	   * A ZWJ before a Halant, requests a subjoined form instead, and hence
+	   * search continues.  This is particularly important for Bengali
+	   * sequence Ra,H,Ya that should form Ya-Phalaa by subjoining Ya. */
+	  if (start < i &&
+	      info[i].indic_category() == I_Cat(ZWJ) &&
+	      info[i - 1].indic_category() == I_Cat(H))
+	    break;
+	}
+      } while (i > limit);
+    }
+
+    /* -> If the syllable starts with Ra + Halant (in a script that has Reph)
+     *    and has more than one consonant, Ra is excluded from candidates for
+     *    base consonants.
+     *
+     *  Only do this for unforced Reph. (ie. not for Ra,H,ZWJ. */
+    if (has_reph && base == start && limit - base <= 2) {
+      /* Have no other consonant, so Reph is not formed and Ra becomes base. */
+      has_reph = false;
+    }
+  }
+
+
+  /* 2. Decompose and reorder Matras:
+   *
+   * Each matra and any syllable modifier sign in the syllable are moved to the
+   * appropriate position relative to the consonant(s) in the syllable. The
+   * shaping engine decomposes two- or three-part matras into their constituent
+   * parts before any repositioning. Matra characters are classified by which
+   * consonant in a conjunct they have affinity for and are reordered to the
+   * following positions:
+   *
+   *   o Before first half form in the syllable
+   *   o After subjoined consonants
+   *   o After post-form consonant
+   *   o After main consonant (for above marks)
+   *
+   * IMPLEMENTATION NOTES:
+   *
+   * The normalize() routine has already decomposed matras for us, so we don't
+   * need to worry about that.
+   */
+
+
+  /* 3.  Reorder marks to canonical order:
+   *
+   * Adjacent nukta and halant or nukta and vedic sign are always repositioned
+   * if necessary, so that the nukta is first.
+   *
+   * IMPLEMENTATION NOTES:
+   *
+   * We don't need to do this: the normalize() routine already did this for us.
+   */
+
+
+  /* Reorder characters */
+
+  for (unsigned int i = start; i < base; i++)
+    info[i].indic_position() = hb_min (POS_PRE_C, (indic_position_t) info[i].indic_position());
+
+  if (base < end)
+    info[base].indic_position() = POS_BASE_C;
+
+  /* Handle beginning Ra */
+  if (has_reph)
+    info[start].indic_position() = POS_RA_TO_BECOME_REPH;
+
+  /* For old-style Indic script tags, move the first post-base Halant after
+   * last consonant.
+   *
+   * Reports suggest that in some scripts Uniscribe does this only if there
+   * is *not* a Halant after last consonant already.  We know that is the
+   * case for Kannada, while it reorders unconditionally in other scripts,
+   * eg. Malayalam, Bengali, and Devanagari.  We don't currently know about
+   * other scripts, so we block Kannada.
+   *
+   * Kannada test case:
+   * U+0C9A,U+0CCD,U+0C9A,U+0CCD
+   * With some versions of Lohit Kannada.
+   * https://bugs.freedesktop.org/show_bug.cgi?id=59118
+   *
+   * Malayalam test case:
+   * U+0D38,U+0D4D,U+0D31,U+0D4D,U+0D31,U+0D4D
+   * With lohit-ttf-20121122/Lohit-Malayalam.ttf
+   *
+   * Bengali test case:
+   * U+0998,U+09CD,U+09AF,U+09CD
+   * With Windows XP vrinda.ttf
+   * https://github.com/harfbuzz/harfbuzz/issues/1073
+   *
+   * Devanagari test case:
+   * U+091F,U+094D,U+0930,U+094D
+   * With chandas.ttf
+   * https://github.com/harfbuzz/harfbuzz/issues/1071
+   */
+  if (indic_plan->is_old_spec)
+  {
+    bool disallow_double_halants = buffer->props.script == HB_SCRIPT_KANNADA;
+    for (unsigned int i = base + 1; i < end; i++)
+      if (info[i].indic_category() == I_Cat(H))
+      {
+	unsigned int j;
+	for (j = end - 1; j > i; j--)
+	  if (is_consonant (info[j]) ||
+	      (disallow_double_halants && info[j].indic_category() == I_Cat(H)))
+	    break;
+	if (info[j].indic_category() != I_Cat(H) && j > i) {
+	  /* Move Halant to after last consonant. */
+	  hb_glyph_info_t t = info[i];
+	  memmove (&info[i], &info[i + 1], (j - i) * sizeof (info[0]));
+	  info[j] = t;
+	}
+	break;
+      }
+  }
+
+  /* Attach misc marks to previous char to move with them. */
+  {
+    indic_position_t last_pos = POS_START;
+    for (unsigned int i = start; i < end; i++)
+    {
+      if ((FLAG_UNSAFE (info[i].indic_category()) & (JOINER_FLAGS | FLAG (I_Cat(N)) | FLAG (I_Cat(RS)) | FLAG (I_Cat(CM)) | FLAG (I_Cat(H)))))
+      {
+	info[i].indic_position() = last_pos;
+	if (unlikely (info[i].indic_category() == I_Cat(H) &&
+		      info[i].indic_position() == POS_PRE_M))
+	{
+	  /*
+	   * Uniscribe doesn't move the Halant with Left Matra.
+	   * TEST: U+092B,U+093F,U+094D
+	   * We follow.
+	   */
+	  for (unsigned int j = i; j > start; j--)
+	    if (info[j - 1].indic_position() != POS_PRE_M) {
+	      info[i].indic_position() = info[j - 1].indic_position();
+	      break;
+	    }
+	}
+      } else if (info[i].indic_position() != POS_SMVD) {
+	if (info[i].indic_category() == I_Cat(MPst) &&
+	    i > start && info[i - 1].indic_category() == I_Cat(SM))
+	  info[i - 1].indic_position() = info[i].indic_position();
+	last_pos = (indic_position_t) info[i].indic_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].indic_position() < POS_SMVD)
+	    info[j].indic_position() = info[i].indic_position();
+	last = i;
+      } else if (FLAG_UNSAFE (info[i].indic_category()) & (FLAG (I_Cat(M)) | FLAG (I_Cat(MPst))))
+	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_indic_order);
+
+    /* Find base again; also flip left-matra sequence. */
+    unsigned first_left_matra = end;
+    unsigned last_left_matra = end;
+    base = end;
+    for (unsigned int i = start; i < end; i++)
+    {
+      if (info[i].indic_position() == POS_BASE_C)
+      {
+	base = i;
+	break;
+      }
+      else if (info[i].indic_position() == POS_PRE_M)
+      {
+        if (first_left_matra == end)
+	  first_left_matra = i;
+	last_left_matra = i;
+      }
+    }
+    /* https://github.com/harfbuzz/harfbuzz/issues/3863 */
+    if (first_left_matra < last_left_matra)
+    {
+      /* No need to merge clusters, handled later. */
+      buffer->reverse_range (first_left_matra, last_left_matra + 1);
+      /* Reverse back nuktas, etc. */
+      unsigned i = first_left_matra;
+      for (unsigned j = i; j <= last_left_matra; j++)
+	if (FLAG_UNSAFE (info[j].indic_category()) & (FLAG (I_Cat(M)) | FLAG (I_Cat(MPst))))
+	{
+	  buffer->reverse_range (i, j + 1);
+	  i = j + 1;
+	}
+    }
+
+    /* Things are out-of-control for post base positions, they may shuffle
+     * around like crazy.  In old-spec mode, we move halants around, so in
+     * that case merge all clusters after base.  Otherwise, check the sort
+     * order and merge as needed.
+     * For pre-base stuff, we handle cluster issues in final reordering.
+     *
+     * We could use buffer->sort() for this, if there was no special
+     * reordering of pre-base stuff happening later...
+     * We don't want to merge_clusters all of that, which buffer->sort()
+     * would.  Here's a concrete example:
+     *
+     * Assume there's a pre-base consonant and explicit Halant before base,
+     * followed by a prebase-reordering (left) Matra:
+     *
+     *   C,H,ZWNJ,B,M
+     *
+     * At this point in reordering we would have:
+     *
+     *   M,C,H,ZWNJ,B
+     *
+     * whereas in final reordering we will bring the Matra closer to Base:
+     *
+     *   C,H,ZWNJ,M,B
+     *
+     * That's why we don't want to merge-clusters anything before the Base
+     * at this point.  But if something moved from after Base to before it,
+     * we should merge clusters from base to them.  In final-reordering, we
+     * only move things around before base, and merge-clusters up to base.
+     * These two merge-clusters from the two sides of base will interlock
+     * to merge things correctly.  See:
+     * https://github.com/harfbuzz/harfbuzz/issues/2272
+     */
+    if (indic_plan->is_old_spec || end - start > 127)
+      buffer->merge_clusters (base, end);
+    else
+    {
+      /* Note!  syllable() is a one-byte field. */
+      for (unsigned int i = base; i < end; i++)
+	if (info[i].syllable() != 255)
+	{
+	  unsigned int min = i;
+	  unsigned int max = i;
+	  unsigned int j = start + info[i].syllable();
+	  while (j != i)
+	  {
+	    min = hb_min (min, j);
+	    max = hb_max (max, j);
+	    unsigned int next = start + info[j].syllable();
+	    info[j].syllable() = 255; /* So we don't process j later again. */
+	    j = next;
+	  }
+	  buffer->merge_clusters (hb_max (base, min), 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;
+
+    /* Reph */
+    for (unsigned int i = start; i < end && info[i].indic_position() == POS_RA_TO_BECOME_REPH; i++)
+      info[i].mask |= indic_plan->mask_array[INDIC_RPHF];
+
+    /* Pre-base */
+    mask = indic_plan->mask_array[INDIC_HALF];
+    if (!indic_plan->is_old_spec &&
+	indic_plan->config->blwf_mode == BLWF_MODE_PRE_AND_POST)
+      mask |= indic_plan->mask_array[INDIC_BLWF];
+    for (unsigned int i = start; i < base; i++)
+      info[i].mask  |= mask;
+    /* Base */
+    mask = 0;
+    if (base < end)
+      info[base].mask |= mask;
+    /* Post-base */
+    mask = indic_plan->mask_array[INDIC_BLWF] |
+	   indic_plan->mask_array[INDIC_ABVF] |
+	   indic_plan->mask_array[INDIC_PSTF];
+    for (unsigned int i = base + 1; i < end; i++)
+      info[i].mask  |= mask;
+  }
+
+  if (indic_plan->is_old_spec &&
+      buffer->props.script == HB_SCRIPT_DEVANAGARI)
+  {
+    /* Old-spec eye-lash Ra needs special handling.  From the
+     * spec:
+     *
+     * "The feature 'below-base form' is applied to consonants
+     * having below-base forms and following the base consonant.
+     * The exception is vattu, which may appear below half forms
+     * as well as below the base glyph. The feature 'below-base
+     * form' will be applied to all such occurrences of Ra as well."
+     *
+     * Test case: U+0924,U+094D,U+0930,U+094d,U+0915
+     * with Sanskrit 2003 font.
+     *
+     * However, note that Ra,Halant,ZWJ is the correct way to
+     * request eyelash form of Ra, so we wouldbn't inhibit it
+     * in that sequence.
+     *
+     * Test case: U+0924,U+094D,U+0930,U+094d,U+200D,U+0915
+     */
+    for (unsigned int i = start; i + 1 < base; i++)
+      if (info[i  ].indic_category() == I_Cat(Ra) &&
+	  info[i+1].indic_category() == I_Cat(H)  &&
+	  (i + 2 == base ||
+	   info[i+2].indic_category() != I_Cat(ZWJ)))
+      {
+	info[i  ].mask |= indic_plan->mask_array[INDIC_BLWF];
+	info[i+1].mask |= indic_plan->mask_array[INDIC_BLWF];
+      }
+  }
+
+  unsigned int pref_len = 2;
+  if (indic_plan->mask_array[INDIC_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 (indic_plan->pref.would_substitute (glyphs, pref_len, face))
+      {
+	for (unsigned int j = 0; j < pref_len; j++)
+	  info[i++].mask |= indic_plan->mask_array[INDIC_PREF];
+	break;
+      }
+    }
+  }
+
+  /* Apply ZWJ/ZWNJ effects */
+  for (unsigned int i = start + 1; i < end; i++)
+    if (is_joiner (info[i])) {
+      bool non_joiner = info[i].indic_category() == I_Cat(ZWNJ);
+      unsigned int j = i;
+
+      do {
+	j--;
+
+	/* ZWJ/ZWNJ should disable CJCT.  They do that by simply
+	 * being there, since we don't skip them for the CJCT
+	 * feature (ie. F_MANUAL_ZWJ) */
+
+	/* A ZWNJ disables HALF. */
+	if (non_joiner)
+	  info[j].mask &= ~indic_plan->mask_array[INDIC_HALF];
+
+      } while (j > start && !is_consonant (info[j]));
+    }
+}
+
+static void
+initial_reordering_standalone_cluster (const hb_ot_shape_plan_t *plan,
+				       hb_face_t *face,
+				       hb_buffer_t *buffer,
+				       unsigned int start, unsigned int end)
+{
+  /* We treat placeholder/dotted-circle as if they are consonants, so we
+   * should just chain.  Only if not in compatibility mode that is... */
+
+  const indic_shape_plan_t *indic_plan = (const indic_shape_plan_t *) plan->data;
+  if (indic_plan->uniscribe_bug_compatible)
+  {
+    /* For dotted-circle, this is what Uniscribe does:
+     * If dotted-circle is the last glyph, it just does nothing.
+     * Ie. It doesn't form Reph. */
+    if (buffer->info[end - 1].indic_category() == I_Cat(DOTTEDCIRCLE))
+      return;
+  }
+
+  initial_reordering_consonant_syllable (plan, face, buffer, start, end);
+}
+
+static void
+initial_reordering_syllable_indic (const hb_ot_shape_plan_t *plan,
+				   hb_face_t *face,
+				   hb_buffer_t *buffer,
+				   unsigned int start, unsigned int end)
+{
+  indic_syllable_type_t syllable_type = (indic_syllable_type_t) (buffer->info[start].syllable() & 0x0F);
+  switch (syllable_type)
+  {
+    case indic_vowel_syllable: /* We made the vowels look like consonants.  So let's call the consonant logic! */
+    case indic_consonant_syllable:
+     initial_reordering_consonant_syllable (plan, face, buffer, start, end);
+     break;
+
+    case indic_broken_cluster: /* We already inserted dotted-circles, so just call the standalone_cluster. */
+    case indic_standalone_cluster:
+     initial_reordering_standalone_cluster (plan, face, buffer, start, end);
+     break;
+
+    case indic_symbol_cluster:
+    case indic_non_indic_cluster:
+      break;
+  }
+}
+
+static bool
+initial_reordering_indic (const hb_ot_shape_plan_t *plan,
+			  hb_font_t *font,
+			  hb_buffer_t *buffer)
+{
+  bool ret = false;
+  if (!buffer->message (font, "start reordering indic initial"))
+    return ret;
+
+  update_consonant_positions_indic (plan, font, buffer);
+  if (hb_syllabic_insert_dotted_circles (font, buffer,
+					 indic_broken_cluster,
+					 I_Cat(DOTTEDCIRCLE),
+					 I_Cat(Repha),
+					 POS_END))
+    ret = true;
+
+  foreach_syllable (buffer, start, end)
+    initial_reordering_syllable_indic (plan, font->face, buffer, start, end);
+
+  (void) buffer->message (font, "end reordering indic initial");
+
+  return ret;
+}
+
+static void
+final_reordering_syllable_indic (const hb_ot_shape_plan_t *plan,
+				 hb_buffer_t *buffer,
+				 unsigned int start, unsigned int end)
+{
+  const indic_shape_plan_t *indic_plan = (const indic_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 I_Cat(H) is desired but has been lost. */
+  /* We don't call load_virama_glyph(), since we know it's already
+   * loaded. */
+  hb_codepoint_t virama_glyph = indic_plan->virama_glyph;
+  if (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_halant() test. */
+	info[i].indic_category() = I_Cat(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 = !!indic_plan->mask_array[INDIC_PREF];
+
+  /* Find base again */
+  unsigned int base;
+  for (base = start; base < end; base++)
+    if (info[base].indic_position() >= POS_BASE_C)
+    {
+      if (try_pref && base + 1 < end)
+      {
+	for (unsigned int i = base + 1; i < end; i++)
+	  if ((info[i].mask & indic_plan->mask_array[INDIC_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_halant (info[base]))
+		base++;
+	      if (base < end)
+		info[base].indic_position() = POS_BASE_C;
+
+	      try_pref = false;
+	    }
+	    break;
+	  }
+	if (base == end)
+	  break;
+      }
+      /* For Malayalam, skip over unformed below- (but NOT post-) forms. */
+      if (buffer->props.script == HB_SCRIPT_MALAYALAM)
+      {
+	for (unsigned int i = base + 1; i < end; i++)
+	{
+	  while (i < end && is_joiner (info[i]))
+	    i++;
+	  if (i == end || !is_halant (info[i]))
+	    break;
+	  i++; /* Skip halant. */
+	  while (i < end && is_joiner (info[i]))
+	    i++;
+	  if (i < end && is_consonant (info[i]) && info[i].indic_position() == POS_BELOW_C)
+	  {
+	    base = i;
+	    info[base].indic_position() = POS_BASE_C;
+	  }
+	}
+      }
+
+      if (start < base && info[base].indic_position() > POS_BASE_C)
+	base--;
+      break;
+    }
+  if (base == end && start < base &&
+      is_one_of (info[base - 1], FLAG (I_Cat(ZWJ))))
+    base--;
+  if (base < end)
+    while (start < base &&
+	   is_one_of (info[base], (FLAG (I_Cat(N)) | FLAG (I_Cat(H)))))
+      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.
+   *
+   * IMPLEMENTATION NOTES:
+   *
+   * It looks like the last sentence is wrong.  Testing, with Windows 7 Uniscribe
+   * and Devanagari shows that the behavior is best described as:
+   *
+   * "If ZWJ follows this halant, matra is NOT repositioned after this halant.
+   *  If ZWNJ follows this halant, position is moved after it."
+   *
+   * Test case, with Adobe Devanagari or Nirmala UI:
+   *
+   *   U+091F,U+094D,U+200C,U+092F,U+093F
+   *   (Matra moves to the middle, after ZWNJ.)
+   *
+   *   U+091F,U+094D,U+200D,U+092F,U+093F
+   *   (Matra does NOT move, stays to the left.)
+   *
+   * https://github.com/harfbuzz/harfbuzz/issues/1070
+   */
+
+  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;
+
+    /* Malayalam / Tamil do not have "half" forms or explicit virama forms.
+     * The glyphs formed by 'half' are Chillus or ligated explicit viramas.
+     * We want to position matra after them.
+     */
+    if (buffer->props.script != HB_SCRIPT_MALAYALAM && buffer->props.script != HB_SCRIPT_TAMIL)
+    {
+    search:
+      while (new_pos > start &&
+	     !(is_one_of (info[new_pos], (FLAG (I_Cat(M)) | FLAG (I_Cat(MPst)) | FLAG (I_Cat(H))))))
+	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_halant (info[new_pos]) &&
+	  info[new_pos].indic_position() != POS_PRE_M)
+      {
+#if 0 // See comment above
+	/* -> 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++;
+#endif
+	if (new_pos + 1 < end)
+	{
+	  /* -> If ZWJ follows this halant, matra is NOT repositioned after this halant. */
+	  if (info[new_pos + 1].indic_category() == I_Cat(ZWJ))
+	  {
+	    /* Keep searching. */
+	    if (new_pos > start)
+	    {
+	      new_pos--;
+	      goto search;
+	    }
+	  }
+	  /* -> If ZWNJ follows this halant, position is moved after it.
+	   *
+	   * IMPLEMENTATION NOTES:
+	   *
+	   * This is taken care of by the state-machine. A Halant,ZWNJ is a terminating
+	   * sequence for a consonant syllable; any pre-base matras occurring after it
+	   * will belong to the subsequent syllable.
+	   */
+	}
+      }
+      else
+	new_pos = start; /* No move. */
+    }
+
+    if (start < new_pos && info[new_pos].indic_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].indic_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, hb_min (end, base + 1));
+
+	  new_pos--;
+	}
+    } else {
+      for (unsigned int i = start; i < base; i++)
+	if (info[i].indic_position () == POS_PRE_M) {
+	  buffer->merge_clusters (i, hb_min (end, base + 1));
+	  break;
+	}
+    }
+  }
+
+
+  /*   o Reorder reph:
+   *
+   *     Reph’s original position is always at the beginning of the syllable,
+   *     (i.e. it is not reordered at the character reordering stage). However,
+   *     it will be reordered according to the basic-forms shaping results.
+   *     Possible positions for reph, depending on the script, are; after main,
+   *     before post-base consonant forms, and after post-base consonant forms.
+   */
+
+  /* Two cases:
+   *
+   * - If repha is encoded as a sequence of characters (Ra,H or Ra,H,ZWJ), then
+   *   we should only move it if the sequence ligated to the repha form.
+   *
+   * - If repha is encoded separately and in the logical position, we should only
+   *   move it if it did NOT ligate.  If it ligated, it's probably the font trying
+   *   to make it work without the reordering.
+   */
+  if (start + 1 < end &&
+      info[start].indic_position() == POS_RA_TO_BECOME_REPH &&
+      ((info[start].indic_category() == I_Cat(Repha)) ^
+       _hb_glyph_info_ligated_and_didnt_multiply (&info[start])))
+  {
+    unsigned int new_reph_pos;
+    reph_position_t reph_pos = indic_plan->config->reph_pos;
+
+    /*       1. If reph should be positioned after post-base consonant forms,
+     *          proceed to step 5.
+     */
+    if (reph_pos == REPH_POS_AFTER_POST)
+    {
+      goto reph_step_5;
+    }
+
+    /*       2. If the reph repositioning class is not after post-base: target
+     *          position is after the first explicit halant glyph between the
+     *          first post-reph consonant and last main consonant. If ZWJ or ZWNJ
+     *          are following this halant, position is moved after it. If such
+     *          position is found, this is the target position. Otherwise,
+     *          proceed to the next step.
+     *
+     *          Note: in old-implementation fonts, where classifications were
+     *          fixed in shaping engine, there was no case where reph position
+     *          will be found on this step.
+     */
+    {
+      new_reph_pos = start + 1;
+      while (new_reph_pos < base && !is_halant (info[new_reph_pos]))
+	new_reph_pos++;
+
+      if (new_reph_pos < base && is_halant (info[new_reph_pos]))
+      {
+	/* ->If ZWJ or ZWNJ are following this halant, position is moved after it. */
+	if (new_reph_pos + 1 < base && is_joiner (info[new_reph_pos + 1]))
+	  new_reph_pos++;
+	goto reph_move;
+      }
+    }
+
+    /*       3. If reph should be repositioned after the main consonant: find the
+     *          first consonant not ligated with main, or find the first
+     *          consonant that is not a potential pre-base-reordering Ra.
+     */
+    if (reph_pos == REPH_POS_AFTER_MAIN)
+    {
+      new_reph_pos = base;
+      while (new_reph_pos + 1 < end && info[new_reph_pos + 1].indic_position() <= POS_AFTER_MAIN)
+	new_reph_pos++;
+      if (new_reph_pos < end)
+	goto reph_move;
+    }
+
+    /*       4. If reph should be positioned before post-base consonant, find
+     *          first post-base classified consonant not ligated with main. If no
+     *          consonant is found, the target position should be before the
+     *          first matra, syllable modifier sign or vedic sign.
+     */
+    /* This is our take on what step 4 is trying to say (and failing, BADLY). */
+    if (reph_pos == REPH_POS_AFTER_SUB)
+    {
+      new_reph_pos = base;
+      while (new_reph_pos + 1 < end &&
+	     !( FLAG_UNSAFE (info[new_reph_pos + 1].indic_position()) & (FLAG (POS_POST_C) | FLAG (POS_AFTER_POST) | FLAG (POS_SMVD))))
+	new_reph_pos++;
+      if (new_reph_pos < end)
+	goto reph_move;
+    }
+
+    /*       5. If no consonant is found in steps 3 or 4, move reph to a position
+     *          immediately before the first post-base matra, syllable modifier
+     *          sign or vedic sign that has a reordering class after the intended
+     *          reph position. For example, if the reordering position for reph
+     *          is post-main, it will skip above-base matras that also have a
+     *          post-main position.
+     */
+    reph_step_5:
+    {
+      /* Copied from step 2. */
+      new_reph_pos = start + 1;
+      while (new_reph_pos < base && !is_halant (info[new_reph_pos]))
+	new_reph_pos++;
+
+      if (new_reph_pos < base && is_halant (info[new_reph_pos]))
+      {
+	/* ->If ZWJ or ZWNJ are following this halant, position is moved after it. */
+	if (new_reph_pos + 1 < base && is_joiner (info[new_reph_pos + 1]))
+	  new_reph_pos++;
+	goto reph_move;
+      }
+    }
+    /* See https://github.com/harfbuzz/harfbuzz/issues/2298#issuecomment-615318654 */
+
+    /*       6. Otherwise, reorder reph to the end of the syllable.
+     */
+    {
+      new_reph_pos = end - 1;
+      while (new_reph_pos > start && info[new_reph_pos].indic_position() == POS_SMVD)
+	new_reph_pos--;
+
+      /*
+       * If the Reph is to be ending up after a Matra,Halant sequence,
+       * position it before that Halant so it can interact with the Matra.
+       * However, if it's a plain Consonant,Halant we shouldn't do that.
+       * Uniscribe doesn't do this.
+       * TEST: U+0930,U+094D,U+0915,U+094B,U+094D
+       */
+      if (!indic_plan->uniscribe_bug_compatible &&
+	  unlikely (is_halant (info[new_reph_pos])))
+      {
+	for (unsigned int i = base + 1; i < new_reph_pos; i++)
+	  if (FLAG_UNSAFE (info[i].indic_category()) & (FLAG (I_Cat(M)) | FLAG (I_Cat(MPst))))
+	  {
+	    /* Ok, got it. */
+	    new_reph_pos--;
+	  }
+      }
+
+      goto reph_move;
+    }
+
+    reph_move:
+    {
+      /* Move */
+      buffer->merge_clusters (start, new_reph_pos + 1);
+      hb_glyph_info_t reph = info[start];
+      memmove (&info[start], &info[start + 1], (new_reph_pos - start) * sizeof (info[0]));
+      info[new_reph_pos] = reph;
+
+      if (start < base && base <= new_reph_pos)
+	base--;
+    }
+  }
+
+
+  /*   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 & indic_plan->mask_array[INDIC_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;
+	  /* Malayalam / Tamil do not have "half" forms or explicit virama forms.
+	   * The glyphs formed by 'half' are Chillus or ligated explicit viramas.
+	   * We want to position matra after them.
+	   */
+	  if (buffer->props.script != HB_SCRIPT_MALAYALAM && buffer->props.script != HB_SCRIPT_TAMIL)
+	  {
+	    while (new_pos > start &&
+		   !(is_one_of (info[new_pos - 1], FLAG (I_Cat(M)) | FLAG (I_Cat(MPst)) | FLAG (I_Cat(H)))))
+	      new_pos--;
+	  }
+
+	  if (new_pos > start && is_halant (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;
+      }
+  }
+
+
+  /* Apply 'init' to the Left Matra if it's a word start. */
+  if (info[start].indic_position () == POS_PRE_M)
+  {
+    if (!start ||
+	!(FLAG_UNSAFE (_hb_glyph_info_get_general_category (&info[start - 1])) &
+	 FLAG_RANGE (HB_UNICODE_GENERAL_CATEGORY_FORMAT, HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)))
+      info[start].mask |= indic_plan->mask_array[INDIC_INIT];
+    else
+      buffer->unsafe_to_break (start - 1, start + 1);
+  }
+
+
+  /*
+   * Finish off the clusters and go home!
+   */
+  if (indic_plan->uniscribe_bug_compatible)
+  {
+    switch ((hb_tag_t) plan->props.script)
+    {
+      case HB_SCRIPT_TAMIL:
+	break;
+
+      default:
+	/* Uniscribe merges the entire syllable into a single cluster... Except for Tamil.
+	 * 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);
+	break;
+    }
+  }
+}
+
+
+static bool
+final_reordering_indic (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 false;
+
+  if (buffer->message (font, "start reordering indic final")) {
+    foreach_syllable (buffer, start, end)
+      final_reordering_syllable_indic (plan, buffer, start, end);
+    (void) buffer->message (font, "end reordering indic final");
+  }
+
+  HB_BUFFER_DEALLOCATE_VAR (buffer, indic_category);
+  HB_BUFFER_DEALLOCATE_VAR (buffer, indic_position);
+
+  return false;
+}
+
+
+static void
+preprocess_text_indic (const hb_ot_shape_plan_t *plan,
+		       hb_buffer_t              *buffer,
+		       hb_font_t                *font)
+{
+  const indic_shape_plan_t *indic_plan = (const indic_shape_plan_t *) plan->data;
+  if (!indic_plan->uniscribe_bug_compatible)
+    _hb_preprocess_text_vowel_constraints (plan, buffer, font);
+}
+
+static bool
+decompose_indic (const hb_ot_shape_normalize_context_t *c,
+		 hb_codepoint_t  ab,
+		 hb_codepoint_t *a,
+		 hb_codepoint_t *b)
+{
+  switch (ab)
+  {
+    /* Don't decompose these. */
+    case 0x0931u  : return false; /* DEVANAGARI LETTER RRA */
+    // https://github.com/harfbuzz/harfbuzz/issues/779
+    case 0x09DCu  : return false; /* BENGALI LETTER RRA */
+    case 0x09DDu  : return false; /* BENGALI LETTER RHA */
+    case 0x0B94u  : return false; /* TAMIL LETTER AU */
+
+
+    /*
+     * Decompose split matras that don't have Unicode decompositions.
+     */
+
+#if 0
+    /* Gujarati */
+    /* This one has no decomposition in Unicode, but needs no decomposition either. */
+    /* case 0x0AC9u  : return false; */
+
+    /* Oriya */
+    case 0x0B57u  : *a = no decomp, -> RIGHT; return true;
+#endif
+  }
+
+  return (bool) c->unicode->decompose (ab, a, b);
+}
+
+static bool
+compose_indic (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;
+
+  /* Composition-exclusion exceptions that we want to recompose. */
+  if (a == 0x09AFu && b == 0x09BCu) { *ab = 0x09DFu; return true; }
+
+  return (bool) c->unicode->compose (a, b, ab);
+}
+
+
+const hb_ot_shaper_t _hb_ot_shaper_indic =
+{
+  collect_features_indic,
+  override_features_indic,
+  data_create_indic,
+  data_destroy_indic,
+  preprocess_text_indic,
+  nullptr, /* postprocess_glyphs */
+  decompose_indic,
+  compose_indic,
+  setup_masks_indic,
+  nullptr, /* reorder_marks */
+  HB_TAG_NONE, /* gpos_tag */
+  HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_DIACRITICS_NO_SHORT_CIRCUIT,
+  HB_OT_SHAPE_ZERO_WIDTH_MARKS_NONE,
+  false, /* fallback_position */
+};
+
+
+#endif