Re-implement hb_set_t::del_range (#2194)

* optimize hb_set_del_range()

fix issue #2193

* fixed bug & added tests

* coding & comment tweaks

src/hb-set.hh

@@ -89,6 +89,23 @@ struct hb_set_t
       }
     }
 
+    void del_range (hb_codepoint_t a, hb_codepoint_t b)
+    {
+      elt_t *la = &elt (a);
+      elt_t *lb = &elt (b);
+      if (la == lb)
+	*la &= ~((mask (b) << 1) - mask(a));
+      else
+      {
+	*la &= mask (a) - 1;
+	la++;
+
+	memset (la, 0, (char *) lb - (char *) la);
+
+	*lb &= ~((mask (b) << 1) - 1);
+      }
+    }
+
     bool is_equal (const page_t *other) const
     {
       return 0 == hb_memcmp (&v, &other->v, sizeof (v));
@@ -366,14 +383,55 @@ struct hb_set_t
     dirty ();
     page->del (g);
   }
+
+  private:
+  void del_pages (int ds, int de)
+  {
+    if (ds <= de)
+    {
+      unsigned int write_index = 0;
+      for (unsigned int i = 0; i < page_map.length; i++)
+      {
+	int m = (int) page_map[i].major;
+	if (m < ds || de < m)
+	  page_map[write_index++] = page_map[i];
+      }
+      compact (write_index);
+    }
+  }
+
+  public:
   void del_range (hb_codepoint_t a, hb_codepoint_t b)
   {
     /* TODO perform op even if !successful. */
-    /* TODO Optimize, like add_range(). */
     if (unlikely (!successful)) return;
-    for (unsigned int i = a; i < b + 1; i++)
-      del (i);
+    if (unlikely (a > b || a == INVALID || b == INVALID)) return;
+    dirty ();
+    unsigned int ma = get_major (a);
+    unsigned int mb = get_major (b);
+    /* Delete pages from ds through de if ds <= de. */
+    int ds = (a == major_start (ma))? (int) ma: (int) (ma + 1);
+    int de = (b + 1 == major_start (mb + 1))? (int) mb: ((int) mb - 1);
+    if (ds > de || (int) ma < ds)
+    {
+      page_t *page = page_for (a);
+      if (page)
+      {
+	if (ma == mb)
+	  page->del_range (a, b);
+	else
+	  page->del_range (a, major_start (ma + 1) - 1);
+      }
+    }
+    if (de < (int) mb && ma != mb)
+    {
+      page_t *page = page_for (b);
+      if (page)
+	page->del_range (major_start (mb), b);
+    }
+    del_pages (ds, de);
   }
+
   bool get (hb_codepoint_t g) const
   {
     const page_t *page = page_for (g);

test/api/test-set.c

@@ -470,6 +470,53 @@ test_set_empty (void)
   hb_set_destroy (b);
 }
 
+static void
+test_set_delrange (void)
+{
+  const unsigned P = 512;	/* Page size. */
+  struct { unsigned b, e; } ranges[] = {
+    { 35, P-15 },		/* From page middle thru middle. */
+    { P, P+100 },		/* From page start thru middle. */
+    { P+300, P*2-1 },		/* From page middle thru end. */
+    { P*3, P*4+100 },		/* From page start thru next page middle. */
+    { P*4+300, P*6-1 },		/* From page middle thru next page end. */
+    { P*6+200,P*8+100 },	/* From page middle covering one page thru page middle. */
+    { P*9, P*10+105 },		/* From page start covering one page thru page middle. */
+    { P*10+305, P*12-1 },	/* From page middle covering one page thru page end. */
+    { P*13, P*15-1 },		/* From page start covering two pages thru page end. */
+    { P*15+100, P*18+100 }	/* From page middle covering two pages thru page middle. */
+  };
+  unsigned n = sizeof (ranges) / sizeof(ranges[0]);
+
+  hb_set_t *s = hb_set_create ();
+
+  test_empty (s);
+  for (unsigned int g = 0; g < ranges[n - 1].e + P; g += 2)
+    hb_set_add (s, g);
+
+  hb_set_add (s, P*2-1);
+  hb_set_add (s, P*6-1);
+  hb_set_add (s, P*12-1);
+  hb_set_add (s, P*15-1);
+
+  for (unsigned i = 0; i < n; i++)
+    hb_set_del_range (s, ranges[i].b, ranges[i].e);
+    
+  hb_set_del_range (s, P*13+5, P*15-10);	/* Deletion from deleted pages. */
+
+  for (unsigned i = 0; i < n; i++)
+  {
+    unsigned b = ranges[i].b;
+    unsigned e = ranges[i].e;
+    g_assert (hb_set_has (s, (b-2)&~1));
+    while (b <= e)
+      g_assert (!hb_set_has (s, b++));
+    g_assert (hb_set_has (s, (e+2)&~1));
+  }
+
+  hb_set_destroy (s);
+}
+
 int
 main (int argc, char **argv)
 {
@@ -479,6 +526,7 @@ main (int argc, char **argv)
   hb_test_add (test_set_algebra);
   hb_test_add (test_set_iter);
   hb_test_add (test_set_empty);
+  hb_test_add (test_set_delrange);
 
   hb_test_add (test_set_intersect_empty);
   hb_test_add (test_set_intersect_page_reduction);