diff --git a/src/gen-ucd.py b/src/gen-ucd.py
index c1594f7b9..9d51ea7e6 100755
--- a/src/gen-ucd.py
+++ b/src/gen-ucd.py
@@ -14,29 +14,26 @@ ucd = youseedy.load_ucdxml (sys.argv[1])
 
 gc = [u['gc'] for u in ucd]
 ccc = [int(u['ccc']) for u in ucd]
-sc = [u['sc'] for u in ucd]
 bmg = [int(v, 16) - int(u) if v else 0 for u,v in enumerate(u['bmg'] for u in ucd)]
+#gc_ccc_non0 = set((cat,klass) for cat,klass in zip(gc,ccc) if klass)
+#gc_bmg_non0 = set((cat,mirr) for cat,mirr in zip(gc, bmg) if mirr)
+
+sc = [u['sc'] for u in ucd]
+
 dm = {i:tuple(int(v, 16) for v in u['dm'].split()) for i,u in enumerate(ucd)
       if u['dm'] != '#' and u['dt'] == 'can' and not (0xAC00 <= i < 0xAC00+11172)}
-
-gc_set = set(gc)
-gc_ccc_non0 = set((cat,klass) for cat,klass in zip(gc,ccc) if klass)
-gc_bmg_non0 = set((cat,mirr) for cat,mirr in zip(gc, bmg) if mirr)
-dm2 = set(v for v in dm.values() if len(v) == 2)
-dm1 = set(v[0] for i,v in dm.items() if len(v) == 1)
-dmx = set(v for v in dm.values() if len(v) not in (1,2))
-assert not dmx
-
-#print(len(sorted(gc_set)))
-#print(len(sorted(gc_ccc_non0)))
-#print(len(sorted(gc_bmg_non0)))
-#print("GC, CCC, and BMG fit in one byte. Compress together.")
-#print()
-
-#print(len(dm))
-#print(len(dm1), min(dm1), max(dm1))
-#print(len(dm2))
-#print(len(sorted(set(v // 512 for v in dm1))))
+assert not any(v for v in dm.values() if len(v) not in (1,2))
+dm1 = sorted(set(v for v in dm.values() if len(v) == 1))
+dm1_array = ['0x%04Xu' % v for v in dm1]
+dm1_order = {v:i+1 for i,v in enumerate(dm1)}
+dm2 = sorted((v, i) for i,v in dm.items() if len(v) == 2)
+dm2 = [("_HB_UCD_ENCODE3 (0x%04Xu, 0x%04Xu, 0x%04Xu)" % (v+(i,)), v) for v,i in dm2]
+dm2_array = [s for s,v in dm2]
+l = 1 + len(dm1_array)
+dm2_order = {v[1]:i+l for i,v in enumerate(dm2)}
+dm_order = {None: 0}
+dm_order.update(dm1_order)
+dm_order.update(dm2_order)
 
 gc_order = packTab.AutoMapping()
 for _ in ('Cc', 'Cf', 'Cn', 'Co', 'Cs', 'Ll', 'Lm', 'Lo', 'Lt', 'Lu',
@@ -67,6 +64,8 @@ print('#include <stdint.h>')
 print()
 code = packTab.Code('_hb_ucd')
 sc_array, _, _ = code.addArray('hb_script_t', 'sc_map', sc_array)
+dm1_array, _, _ = code.addArray('hb_codepoint_t', 'dm1_map', dm1_array)
+dm2_array, _, _ = code.addArray('uint64_t', 'dm2_map', dm2_array)
 code.print_c(linkage='static inline')
 
 for compression in (DEFAULT, COMPACT):
@@ -83,6 +82,7 @@ for compression in (DEFAULT, COMPACT):
     packTab.pack_table(ccc, 0, compression=compression).genCode(code, 'ccc')
     packTab.pack_table(bmg, 0, compression=compression).genCode(code, 'bmg')
     packTab.pack_table(sc, 'Zzzz', mapping=sc_order, compression=compression).genCode(code, 'sc')
+    packTab.pack_table(dm, None, mapping=dm_order, compression=compression).genCode(code, 'dm')
 
     code.print_c(linkage='static inline')