--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mupdf-source/thirdparty/harfbuzz/src/OT/Layout/GSUB/AlternateSubst.hh	Mon Sep 15 11:43:07 2025 +0200
@@ -0,0 +1,62 @@
+#ifndef OT_LAYOUT_GSUB_ALTERNATESUBST_HH
+#define OT_LAYOUT_GSUB_ALTERNATESUBST_HH
+
+#include "AlternateSubstFormat1.hh"
+#include "Common.hh"
+
+namespace OT {
+namespace Layout {
+namespace GSUB_impl {
+
+struct AlternateSubst
+{
+  protected:
+  union {
+  HBUINT16				format;         /* Format identifier */
+  AlternateSubstFormat1_2<SmallTypes>	format1;
+#ifndef HB_NO_BEYOND_64K
+  AlternateSubstFormat1_2<MediumTypes>	format2;
+#endif
+  } u;
+  public:
+
+  template <typename context_t, typename ...Ts>
+  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
+  {
+    TRACE_DISPATCH (this, u.format);
+    if (unlikely (!c->may_dispatch (this, &u.format))) return_trace (c->no_dispatch_return_value ());
+    switch (u.format) {
+    case 1: return_trace (c->dispatch (u.format1, std::forward<Ts> (ds)...));
+#ifndef HB_NO_BEYOND_64K
+    case 2: return_trace (c->dispatch (u.format2, std::forward<Ts> (ds)...));
+#endif
+    default:return_trace (c->default_return_value ());
+    }
+  }
+
+  /* TODO This function is unused and not updated to 24bit GIDs. Should be done by using
+   * iterators. While at it perhaps using iterator of arrays of hb_codepoint_t instead. */
+  bool serialize (hb_serialize_context_t *c,
+                  hb_sorted_array_t<const HBGlyphID16> glyphs,
+                  hb_array_t<const unsigned int> alternate_len_list,
+                  hb_array_t<const HBGlyphID16> alternate_glyphs_list)
+  {
+    TRACE_SERIALIZE (this);
+    if (unlikely (!c->extend_min (u.format))) return_trace (false);
+    unsigned int format = 1;
+    u.format = format;
+    switch (u.format) {
+    case 1: return_trace (u.format1.serialize (c, glyphs, alternate_len_list, alternate_glyphs_list));
+    default:return_trace (false);
+    }
+  }
+
+  /* TODO subset() should choose format. */
+
+};
+
+}
+}
+}
+
+#endif  /* OT_LAYOUT_GSUB_ALTERNATESUBST_HH */