[set] Add backwards iterator

New API:
- hb_set_previous()
- hb_set_previous_range()

5 files changed, 194 insertions, 8 deletions

diff --git a/docs/harfbuzz-sections.txt b/docs/harfbuzz-sections.txt
index 5df33a81..91faa0b7 100644
--- a/docs/harfbuzz-sections.txt
+++ b/docs/harfbuzz-sections.txt
@@ -528,7 +528,9 @@ hb_set_intersect
 hb_set_is_empty
 hb_set_is_equal
 hb_set_next
+hb_set_previous
 hb_set_next_range
+hb_set_previous_range
 hb_set_reference
 hb_set_set
 hb_set_set_user_data
diff --git a/src/hb-set-private.hh b/src/hb-set-private.hh
index 45963487..7282b079 100644
--- a/src/hb-set-private.hh
+++ b/src/hb-set-private.hh
@@ -125,6 +125,33 @@ struct hb_set_t
       *codepoint = i * ELT_BITS + j;
       return true;
     }
+    inline bool previous (hb_codepoint_t *codepoint) const
+    {
+      unsigned int m = (*codepoint - 1) & MASK;
+      if (m == MASK)
+      {
+	*codepoint = INVALID;
+	return false;
+      }
+      unsigned int i = m / ELT_BITS;
+      unsigned int j = m & ELT_MASK;
+
+      for (; (int) j >= 0; j--)
+        if (v[i] & (elt_t (1) << j))
+	  goto found;
+      for (i--; (int) i >= 0; i--)
+        if (v[i])
+	  for (j = ELT_BITS - 1; (int) j >= 0; j--)
+	    if (v[i] & (elt_t (1) << j))
+	      goto found;
+
+      *codepoint = INVALID;
+      return false;
+
+    found:
+      *codepoint = i * ELT_BITS + j;
+      return true;
+    }
     inline hb_codepoint_t get_min (void) const
     {
       for (unsigned int i = 0; i < len (); i++)
@@ -476,7 +503,7 @@ struct hb_set_t
       if (pages[page_map[i].index].next (codepoint))
       {
 	*codepoint += page_map[i].major * page_t::PAGE_BITS;
-        return true;
+	return true;
       }
       i++;
     }
@@ -492,6 +519,37 @@ struct hb_set_t
     *codepoint = INVALID;
     return false;
   }
+  inline bool previous (hb_codepoint_t *codepoint) const
+  {
+    if (unlikely (*codepoint == INVALID)) {
+      *codepoint = get_max ();
+      return *codepoint != INVALID;
+    }
+
+    page_map_t map = {get_major (*codepoint), 0};
+    unsigned int i;
+    page_map.bfind (map, &i);
+    if (i < page_map.len && page_map[i].major == map.major)
+    {
+      if (pages[page_map[i].index].previous (codepoint))
+      {
+	*codepoint += page_map[i].major * page_t::PAGE_BITS;
+	return true;
+      }
+    }
+    i--;
+    for (; (int) i >= 0; i--)
+    {
+      hb_codepoint_t m = pages[page_map[i].index].get_max ();
+      if (m != INVALID)
+      {
+	*codepoint = page_map[i].major * page_t::PAGE_BITS + m;
+	return true;
+      }
+    }
+    *codepoint = INVALID;
+    return false;
+  }
   inline bool next_range (hb_codepoint_t *first, hb_codepoint_t *last) const
   {
     hb_codepoint_t i;
@@ -503,12 +561,31 @@ struct hb_set_t
       return false;
     }
 
+    /* TODO Speed up. */
     *last = *first = i;
     while (next (&i) && i == *last + 1)
       (*last)++;
 
     return true;
   }
+  inline bool previous_range (hb_codepoint_t *first, hb_codepoint_t *last) const
+  {
+    hb_codepoint_t i;
+
+    i = *first;
+    if (!previous (&i))
+    {
+      *last = *first = INVALID;
+      return false;
+    }
+
+    /* TODO Speed up. */
+    *last = *first = i;
+    while (previous (&i) && i == *first - 1)
+      (*first)--;
+
+    return true;
+  }
 
   inline unsigned int get_population (void) const
   {
diff --git a/src/hb-set.cc b/src/hb-set.cc
index f3b864c1..07cf9d09 100644
--- a/src/hb-set.cc
+++ b/src/hb-set.cc
@@ -437,7 +437,9 @@ hb_set_get_max (const hb_set_t *set)
  * @set: a set.
  * @codepoint: (inout):
  *
- * 
+ * Gets the next number in @set that is greater than current value of @codepoint.
+ *
+ * Set @codepoint to %HB_SET_VALUE_INVALID to get started.
  *
  * Return value: whether there was a next value.
  *
@@ -451,6 +453,26 @@ hb_set_next (const hb_set_t *set,
 }
 
 /**
+ * hb_set_previous:
+ * @set: a set.
+ * @codepoint: (inout):
+ *
+ * Gets the previous number in @set that is slower than current value of @codepoint.
+ *
+ * Set @codepoint to %HB_SET_VALUE_INVALID to get started.
+ *
+ * Return value: whether there was a previous value.
+ *
+ * Since: 1.8.0
+ **/
+hb_bool_t
+hb_set_previous (const hb_set_t *set,
+		 hb_codepoint_t *codepoint)
+{
+  return set->previous (codepoint);
+}
+
+/**
  * hb_set_next_range:
  * @set: a set.
  * @first: (out): output first codepoint in the range.
@@ -459,6 +481,8 @@ hb_set_next (const hb_set_t *set,
  * Gets the next consecutive range of numbers in @set that
  * are greater than current value of @last.
  *
+ * Set @last to %HB_SET_VALUE_INVALID to get started.
+ *
  * Return value: whether there was a next range.
  *
  * Since: 0.9.7
@@ -470,3 +494,26 @@ hb_set_next_range (const hb_set_t *set,
 {
   return set->next_range (first, last);
 }
+
+/**
+ * hb_set_previous_range:
+ * @set: a set.
+ * @first: (inout): input current first and output first codepoint in the range.
+ * @last: (out): output last codepoint in the range.
+ *
+ * Gets the previous consecutive range of numbers in @set that
+ * are greater than current value of @last.
+ *
+ * Set @first to %HB_SET_VALUE_INVALID to get started.
+ *
+ * Return value: whether there was a previous range.
+ *
+ * Since: 1.8.0
+ **/
+hb_bool_t
+hb_set_previous_range (const hb_set_t *set,
+		       hb_codepoint_t *first,
+		       hb_codepoint_t *last)
+{
+  return set->previous_range (first, last);
+}
diff --git a/src/hb-set.h b/src/hb-set.h
index 2ce40607..b0f82f82 100644
--- a/src/hb-set.h
+++ b/src/hb-set.h
@@ -129,25 +129,36 @@ hb_set_symmetric_difference (hb_set_t       *set,
 HB_EXTERN unsigned int
 hb_set_get_population (const hb_set_t *set);
 
-/* Returns -1 if set empty. */
+/* Returns HB_SET_VALUE_INVALID if set empty. */
 HB_EXTERN hb_codepoint_t
 hb_set_get_min (const hb_set_t *set);
 
-/* Returns -1 if set empty. */
+/* Returns HB_SET_VALUE_INVALID if set empty. */
 HB_EXTERN hb_codepoint_t
 hb_set_get_max (const hb_set_t *set);
 
-/* Pass -1 in to get started. */
+/* Pass HB_SET_VALUE_INVALID in to get started. */
 HB_EXTERN hb_bool_t
 hb_set_next (const hb_set_t *set,
 	     hb_codepoint_t *codepoint);
 
-/* Pass -1 for first and last to get started. */
+/* Pass HB_SET_VALUE_INVALID in to get started. */
+HB_EXTERN hb_bool_t
+hb_set_previous (const hb_set_t *set,
+		 hb_codepoint_t *codepoint);
+
+/* Pass HB_SET_VALUE_INVALID for first and last to get started. */
 HB_EXTERN hb_bool_t
 hb_set_next_range (const hb_set_t *set,
 		   hb_codepoint_t *first,
 		   hb_codepoint_t *last);
 
+/* Pass HB_SET_VALUE_INVALID for first and last to get started. */
+HB_EXTERN hb_bool_t
+hb_set_previous_range (const hb_set_t *set,
+		       hb_codepoint_t *first,
+		       hb_codepoint_t *last);
+
 
 HB_END_DECLS
 
diff --git a/test/api/test-set.c b/test/api/test-set.c
index bbea2cf5..60e11d98 100644
--- a/test/api/test-set.c
+++ b/test/api/test-set.c
@@ -32,25 +32,33 @@
 static void
 test_empty (hb_set_t *s)
 {
-  hb_codepoint_t next = HB_SET_VALUE_INVALID;
+  hb_codepoint_t next;
   g_assert_cmpint (hb_set_get_population (s), ==, 0);
   g_assert_cmpint (hb_set_get_min (s), ==, HB_SET_VALUE_INVALID);
   g_assert_cmpint (hb_set_get_max (s), ==, HB_SET_VALUE_INVALID);
   g_assert (!hb_set_has (s, 13));
+  next = 53043;
   g_assert (!hb_set_next (s, &next));
   g_assert_cmpint (next, ==, HB_SET_VALUE_INVALID);
+  next = 07734;
+  g_assert (!hb_set_previous (s, &next));
+  g_assert_cmpint (next, ==, HB_SET_VALUE_INVALID);
   g_assert (hb_set_is_empty (s));
 }
 
 static void
 test_not_empty (hb_set_t *s)
 {
-  hb_codepoint_t next = HB_SET_VALUE_INVALID;
+  hb_codepoint_t next;
   g_assert_cmpint (hb_set_get_population (s), !=, 0);
   g_assert_cmpint (hb_set_get_min (s), !=, HB_SET_VALUE_INVALID);
   g_assert_cmpint (hb_set_get_max (s), !=, HB_SET_VALUE_INVALID);
+  next = HB_SET_VALUE_INVALID;
   g_assert (hb_set_next (s, &next));
   g_assert_cmpint (next, !=, HB_SET_VALUE_INVALID);
+  next = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_previous (s, &next));
+  g_assert_cmpint (next, !=, HB_SET_VALUE_INVALID);
 }
 
 static void
@@ -271,6 +279,27 @@ test_set_iter (void)
   g_assert (!hb_set_next (s, &next));
   g_assert_cmpint (next, ==, HB_SET_VALUE_INVALID);
 
+  next = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_previous (s, &next));
+  g_assert_cmpint (next, ==, 20005);
+  g_assert (hb_set_previous (s, &next));
+  g_assert_cmpint (next, ==, 1200);
+  g_assert (hb_set_previous (s, &next));
+  g_assert_cmpint (next, ==, 1100);
+  g_assert (hb_set_previous (s, &next));
+  g_assert_cmpint (next, ==, 15);
+  g_assert (hb_set_previous (s, &next));
+  g_assert (hb_set_previous (s, &next));
+  g_assert_cmpint (next, ==, 13);
+  g_assert (hb_set_previous (s, &next));
+  g_assert (hb_set_previous (s, &next));
+  g_assert (hb_set_previous (s, &next));
+  g_assert_cmpint (next, ==, 10);
+  g_assert (hb_set_previous (s, &next));
+  g_assert_cmpint (next, ==, 6);
+  g_assert (!hb_set_previous (s, &next));
+  g_assert_cmpint (next, ==, HB_SET_VALUE_INVALID);
+
   first = last = HB_SET_VALUE_INVALID;
   g_assert (hb_set_next_range (s, &first, &last));
   g_assert_cmpint (first, ==, 6);
@@ -291,6 +320,26 @@ test_set_iter (void)
   g_assert_cmpint (first, ==, HB_SET_VALUE_INVALID);
   g_assert_cmpint (last,  ==, HB_SET_VALUE_INVALID);
 
+  first = last = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_previous_range (s, &first, &last));
+  g_assert_cmpint (first, ==, 20005);
+  g_assert_cmpint (last,  ==, 20005);
+  g_assert (hb_set_previous_range (s, &first, &last));
+  g_assert_cmpint (first, ==, 1200);
+  g_assert_cmpint (last,  ==, 1200);
+  g_assert (hb_set_previous_range (s, &first, &last));
+  g_assert_cmpint (first, ==, 1100);
+  g_assert_cmpint (last,  ==, 1100);
+  g_assert (hb_set_previous_range (s, &first, &last));
+  g_assert_cmpint (first, ==, 10);
+  g_assert_cmpint (last,  ==, 15);
+  g_assert (hb_set_previous_range (s, &first, &last));
+  g_assert_cmpint (first, ==, 6);
+  g_assert_cmpint (last,  ==, 6);
+  g_assert (!hb_set_previous_range (s, &first, &last));
+  g_assert_cmpint (first, ==, HB_SET_VALUE_INVALID);
+  g_assert_cmpint (last,  ==, HB_SET_VALUE_INVALID);
+
   hb_set_destroy (s);
 }