From 8775e9b4a4f985ec29bba609b7fc53424f24834c Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Wed, 6 Jul 2022 13:28:17 -0600
Subject: [PATCH] [>64k:layout:SingleSubst] Implement format 3/4

Implements https://github.com/be-fonts/boring-expansion-spec/issues/31
---
 src/OT/Layout/GSUB/SingleSubst.hh        | 32 ++++++++++++++++++++++--
 src/OT/Layout/GSUB/SingleSubstFormat2.hh |  2 +-
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/src/OT/Layout/GSUB/SingleSubst.hh b/src/OT/Layout/GSUB/SingleSubst.hh
index 49d894f50..6942e6997 100644
--- a/src/OT/Layout/GSUB/SingleSubst.hh
+++ b/src/OT/Layout/GSUB/SingleSubst.hh
@@ -16,6 +16,10 @@ struct SingleSubst
   HBUINT16				format;         /* Format identifier */
   SingleSubstFormat1_3<SmallTypes>	format1;
   SingleSubstFormat2_4<SmallTypes>	format2;
+#ifndef HB_NO_BORING_EXPANSION
+  SingleSubstFormat1_3<MediumTypes>	format3;
+  SingleSubstFormat2_4<MediumTypes>	format4;
+#endif
   } u;
 
   public:
@@ -28,6 +32,10 @@ struct SingleSubst
     switch (u.format) {
     case 1: return_trace (c->dispatch (u.format1, std::forward<Ts> (ds)...));
     case 2: return_trace (c->dispatch (u.format2, std::forward<Ts> (ds)...));
+#ifndef HB_NO_BORING_EXPANSION
+    case 3: return_trace (c->dispatch (u.format3, std::forward<Ts> (ds)...));
+    case 4: return_trace (c->dispatch (u.format4, std::forward<Ts> (ds)...));
+#endif
     default:return_trace (c->default_return_value ());
     }
   }
@@ -45,11 +53,24 @@ struct SingleSubst
     if (glyphs)
     {
       format = 1;
+      hb_codepoint_t mask = 0xFFFFu;
+
+#ifndef HB_NO_BORING_EXPANSION
+       if (+ glyphs
+	   | hb_map_retains_sorting (hb_first)
+	   | hb_filter ([] (hb_codepoint_t gid) { return gid > 0xFFFFu; }))
+       {
+	 format += 2;
+	 mask = 0xFFFFFFu;
+       }
+#endif
+
       auto get_delta = [=] (hb_codepoint_pair_t _)
-                       { return (unsigned) (_.second - _.first) & 0xFFFF; };
+                       { return (unsigned) (_.second - _.first) & mask; };
       delta = get_delta (*glyphs);
-      if (!hb_all (++(+glyphs), delta, get_delta)) format = 2;
+      if (!hb_all (++(+glyphs), delta, get_delta)) format += 1;
     }
+
     u.format = format;
     switch (u.format) {
     case 1: return_trace (u.format1.serialize (c,
@@ -57,6 +78,13 @@ struct SingleSubst
                                                | hb_map_retains_sorting (hb_first),
                                                delta));
     case 2: return_trace (u.format2.serialize (c, glyphs));
+#ifndef HB_NO_BORING_EXPANSION
+    case 3: return_trace (u.format3.serialize (c,
+                                               + glyphs
+                                               | hb_map_retains_sorting (hb_first),
+                                               delta));
+    case 4: return_trace (u.format4.serialize (c, glyphs));
+#endif
     default:return_trace (false);
     }
   }
diff --git a/src/OT/Layout/GSUB/SingleSubstFormat2.hh b/src/OT/Layout/GSUB/SingleSubstFormat2.hh
index 57cc0ba4c..386419a2a 100644
--- a/src/OT/Layout/GSUB/SingleSubstFormat2.hh
+++ b/src/OT/Layout/GSUB/SingleSubstFormat2.hh
@@ -104,7 +104,7 @@ struct SingleSubstFormat2_4
     + hb_zip (this+coverage, substitute)
     | hb_filter (glyphset, hb_first)
     | hb_filter (glyphset, hb_second)
-    | hb_map_retains_sorting ([&] (hb_pair_t<hb_codepoint_t, const HBGlyphID16 &> p) -> hb_codepoint_pair_t
+    | hb_map_retains_sorting ([&] (hb_pair_t<hb_codepoint_t, const typename Types::HBGlyphID &> p) -> hb_codepoint_pair_t
                               { return hb_pair (glyph_map[p.first], glyph_map[p.second]); })
     ;