[set] Tune size again

Switch from a 128+64 hierarchy, to 32+32. New page size is 1024.
This should make set iteration faster, without affecting other op
performances much.

src/hb-set-private.hh

@@ -177,11 +177,11 @@ struct hb_set_t
       return 0;
     }
 
-    static const unsigned int PAGE_BITS = 8192; /* Use to tune. */
+    typedef uint32_t elt_t;
+    static const unsigned int ELT_BITS = sizeof (elt_t) * 8;
+    static const unsigned int PAGE_BITS = ELT_BITS * ELT_BITS; /* 1024. Use to tune. */
     static_assert ((PAGE_BITS & ((PAGE_BITS) - 1)) == 0, "");
 
-    typedef uint64_t elt_t;
-
 #if 0 && HAVE_VECTOR_SIZE
     /* The vectorized version does not work with clang as non-const
      * elt() errs "non-const reference cannot bind to vector element". */
@@ -192,7 +192,6 @@ struct hb_set_t
 
     vector_t v;
 
-    static const unsigned int ELT_BITS = sizeof (elt_t) * 8;
     static const unsigned int ELT_MASK = ELT_BITS - 1;
     static const unsigned int BITS = sizeof (vector_t) * 8;
     static const unsigned int MASK = BITS - 1;