* "approximate member query". Conceptually these are like Bloom
* Filter and Quotient Filter, however, much smaller, faster, and
* designed to fit the requirements of our uses for glyph coverage
- * queries. As a result, our filters have much higher.
+ * queries.
+ *
+ * Our filters are highly accurate if the lookup covers fairly local
+ * set of glyphs, but fully flooded and ineffective if coverage is
+ * all over the place.
+ *
+ * The frozen-set can be used instead of a digest, to trade more
+ * memory for 100% accuracy, but in practice, that doesn't look like
+ * an attractive trade-off.
*/
template <typename mask_t, unsigned int shift>
struct hb_set_t
{
+ friend struct hb_frozen_set_t;
+
hb_object_header_t header;
ASSERT_POD ();
bool in_error;
inline void init (void) {
- header.init ();
+ hb_object_init (this);
clear ();
}
inline void fini (void) {
static const hb_codepoint_t INVALID = HB_SET_VALUE_INVALID;
elt_t &elt (hb_codepoint_t g) { return elts[g >> SHIFT]; }
- elt_t elt (hb_codepoint_t g) const { return elts[g >> SHIFT]; }
+ elt_t const &elt (hb_codepoint_t g) const { return elts[g >> SHIFT]; }
elt_t mask (hb_codepoint_t g) const { return elt_t (1) << (g & MASK); }
elt_t elts[ELTS]; /* XXX 8kb */
ASSERT_STATIC (sizeof (elt_t) * 8 * ELTS > MAX_G);
};
+struct hb_frozen_set_t
+{
+ static const unsigned int SHIFT = hb_set_t::SHIFT;
+ static const unsigned int BITS = hb_set_t::BITS;
+ static const unsigned int MASK = hb_set_t::MASK;
+ typedef hb_set_t::elt_t elt_t;
+
+ inline void init (const hb_set_t &set)
+ {
+ start = count = 0;
+ elts = NULL;
+
+ unsigned int max = set.get_max ();
+ if (max == set.INVALID)
+ return;
+ unsigned int min = set.get_min ();
+ const elt_t &min_elt = set.elt (min);
+
+ start = min & ~MASK;
+ count = max - start + 1;
+ unsigned int num_elts = (count + BITS - 1) / BITS;
+ unsigned int elts_size = num_elts * sizeof (elt_t);
+ elts = (elt_t *) malloc (elts_size);
+ if (unlikely (!elts))
+ {
+ start = count = 0;
+ return;
+ }
+ memcpy (elts, &min_elt, elts_size);
+ }
+
+ inline void fini (void)
+ {
+ if (elts)
+ free (elts);
+ }
+
+ inline bool has (hb_codepoint_t g) const
+ {
+ /* hb_codepoint_t is unsigned. */
+ g -= start;
+ if (unlikely (g > count)) return false;
+ return !!(elt (g) & mask (g));
+ }
+
+ elt_t const &elt (hb_codepoint_t g) const { return elts[g >> SHIFT]; }
+ elt_t mask (hb_codepoint_t g) const { return elt_t (1) << (g & MASK); }
+
+ private:
+ hb_codepoint_t start, count;
+ elt_t *elts;
+};
#endif /* HB_SET_PRIVATE_HH */