tor-browser

hb-bit-set.hh (28516B)

---

/*
* Copyright © 2012,2017  Google, Inc.
* Copyright © 2021 Behdad Esfahbod
*
*  This is part of HarfBuzz, a text shaping library.
*
* Permission is hereby granted, without written agreement and without
* license or royalty fees, to use, copy, modify, and distribute this
* software and its documentation for any purpose, provided that the
* above copyright notice and the following two paragraphs appear in
* all copies of this software.
*
* IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
* ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
* IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
* DAMAGE.
*
* THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
* BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
* FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
* ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
*
* Google Author(s): Behdad Esfahbod
*/

#ifndef HB_BIT_SET_HH
#define HB_BIT_SET_HH

#include "hb.hh"
#include "hb-bit-page.hh"


struct hb_bit_set_t
{
 hb_bit_set_t () = default;
 ~hb_bit_set_t () = default;

 hb_bit_set_t (const hb_bit_set_t& other) : hb_bit_set_t () { set (other, true); }
 hb_bit_set_t ( hb_bit_set_t&& other)  noexcept : hb_bit_set_t () { hb_swap (*this, other); }
 hb_bit_set_t& operator= (const hb_bit_set_t& other) { set (other); return *this; }
 hb_bit_set_t& operator= (hb_bit_set_t&& other)  noexcept { hb_swap (*this, other); return *this; }
 friend void swap (hb_bit_set_t &a, hb_bit_set_t &b) noexcept
 {
   if (likely (!a.successful || !b.successful))
     return;
   hb_swap (a.population, b.population);
   hb_swap (a.last_page_lookup, b.last_page_lookup);
   hb_swap (a.page_map, b.page_map);
   hb_swap (a.pages, b.pages);
 }

 void init ()
 {
   successful = true;
   population = 0;
   last_page_lookup = 0;
   page_map.init ();
   pages.init ();
 }
 void fini ()
 {
   page_map.fini ();
   pages.fini ();
 }

 using page_t = hb_bit_page_t;
 struct page_map_t
 {
   int cmp (const page_map_t &o) const { return cmp (o.major); }
   int cmp (uint32_t o_major) const { return (int) o_major - (int) major; }

   uint32_t major;
   uint32_t index;
 };

 bool successful = true; /* Allocations successful */
 mutable unsigned int population = 0;
 mutable hb_atomic_t<unsigned> last_page_lookup = 0;
 hb_sorted_vector_t<page_map_t> page_map;
 hb_vector_t<page_t> pages;

 void err () { if (successful) successful = false; } /* TODO Remove */
 bool in_error () const { return !successful; }

 bool resize (unsigned int count, bool clear = true, bool exact_size = false)
 {
   if (unlikely (!successful)) return false;

   if (pages.length < count && (unsigned) pages.allocated < count && count <= 2)
     exact_size = true; // Most sets are small and local

   if (unlikely (!pages.resize_full (count, clear, exact_size) ||
!page_map.resize_full (count, clear, false)))
   {
     pages.resize_full (page_map.length, clear, exact_size);
     successful = false;
     return false;
   }
   return true;
 }

 void alloc (unsigned sz)
 {
   sz >>= (page_t::PAGE_BITS_LOG_2 - 1);
   pages.alloc (sz);
   page_map.alloc (sz);
 }

 hb_bit_set_t& reset ()
 {
   successful = true;
   clear ();
   return *this;
 }

 void clear ()
 {
   resize (0);
   if (likely (successful))
     population = 0;
 }
 bool is_empty () const
 {
   unsigned int count = pages.length;
   for (unsigned int i = 0; i < count; i++)
     if (!pages[i].is_empty ())
return false;
   return true;
 }
 explicit operator bool () const { return !is_empty (); }

 uint32_t hash () const
 {
   uint32_t h = 0;
   for (auto &map : page_map)
   {
     auto &page = pages.arrayZ[map.index];
     if (unlikely (page.is_empty ())) continue;
     h = h * 31 + hb_hash (map.major) + hb_hash (page);
   }
   return h;
 }

 private:
 void dirty () { population = UINT_MAX; }
 public:

 void add (hb_codepoint_t g)
 {
   if (unlikely (!successful)) return;
   if (unlikely (g == INVALID)) return;
   dirty ();
   page_t *page = page_for (g, true); if (unlikely (!page)) return;
   page->add (g);
 }
 bool add_range (hb_codepoint_t a, hb_codepoint_t b)
 {
   if (unlikely (!successful)) return true; /* https://github.com/harfbuzz/harfbuzz/issues/657 */
   if (unlikely (a > b || a == INVALID || b == INVALID)) return false;
   dirty ();
   unsigned int ma = get_major (a);
   unsigned int mb = get_major (b);
   if (ma == mb)
   {
     page_t *page = page_for (a, true); if (unlikely (!page)) return false;
     page->add_range (a, b);
   }
   else
   {
     page_t *page = page_for (a, true); if (unlikely (!page)) return false;
     page->add_range (a, major_start (ma + 1) - 1);

     for (unsigned int m = ma + 1; m < mb; m++)
     {
page = page_for (major_start (m), true); if (unlikely (!page)) return false;
page->init1 ();
     }

     page = page_for (b, true); if (unlikely (!page)) return false;
     page->add_range (major_start (mb), b);
   }
   return true;
 }

 /* Duplicated here from hb-machinery.hh to avoid including it. */
 template<typename Type>
 static inline const Type& StructAtOffsetUnaligned(const void *P, unsigned int offset)
 {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wcast-align"
   return * reinterpret_cast<const Type*> ((const char *) P + offset);
#pragma GCC diagnostic pop
 }

 template <typename T>
 void set_array (bool v, const T *array, unsigned int count, unsigned int stride=sizeof(T))
 {
   if (unlikely (!successful)) return;
   if (!count) return;
   dirty ();
   hb_codepoint_t g = *array;
   while (count)
   {
     unsigned int m = get_major (g);
     page_t *page = page_for (g, v); if (unlikely (v && !page)) return;
     unsigned int start = major_start (m);
     unsigned int end = major_start (m + 1);
     do
     {
       if (g != INVALID && (v || page)) /* The v check is to optimize out the page check if v is true. */
  page->set (g, v);

array = &StructAtOffsetUnaligned<T> (array, stride);
count--;
     }
     while (count && (g = *array, start <= g && g < end));
   }
 }

 template <typename T>
 void add_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
 { set_array (true, array, count, stride); }
 template <typename T>
 void add_array (const hb_array_t<const T>& arr) { add_array (&arr, arr.len ()); }

 template <typename T>
 void del_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
 { set_array (false, array, count, stride); }
 template <typename T>
 void del_array (const hb_array_t<const T>& arr) { del_array (&arr, arr.len ()); }

 /* Might return false if array looks unsorted.
  * Used for faster rejection of corrupt data. */
 template <typename T>
 bool set_sorted_array (bool v, const T *array, unsigned int count, unsigned int stride=sizeof(T))
 {
   if (unlikely (!successful)) return true; /* https://github.com/harfbuzz/harfbuzz/issues/657 */
   if (unlikely (!count)) return true;
   dirty ();
   hb_codepoint_t g = *array;
   hb_codepoint_t last_g = g;
   while (count)
   {
     unsigned int m = get_major (g);
     page_t *page = page_for (g, v); if (unlikely (v && !page)) return false;
     unsigned int end = major_start (m + 1);
     do
     {
/* If we try harder we can change the following comparison to <=;
 * Not sure if it's worth it. */
if (g < last_g) return false;
last_g = g;

       if (g != INVALID && (v || page)) /* The v check is to optimize out the page check if v is true. */
  page->add (g);

array = &StructAtOffsetUnaligned<T> (array, stride);
count--;
     }
     while (count && (g = *array, g < end));
   }
   return true;
 }

 template <typename T>
 bool add_sorted_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
 { return set_sorted_array (true, array, count, stride); }
 template <typename T>
 bool add_sorted_array (const hb_sorted_array_t<const T>& arr) { return add_sorted_array (&arr, arr.len ()); }

 template <typename T>
 bool del_sorted_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
 { return set_sorted_array (false, array, count, stride); }
 template <typename T>
 bool del_sorted_array (const hb_sorted_array_t<const T>& arr) { return del_sorted_array (&arr, arr.len ()); }

 void del (hb_codepoint_t g)
 {
   if (unlikely (!successful)) return;
   page_t *page = page_for (g);
   if (!page)
     return;
   dirty ();
   page->del (g);
 }

 private:
 void del_pages (int ds, int de)
 {
   if (ds <= de)
   {
     // Pre-allocate the workspace that compact() will need so we can bail on allocation failure
     // before attempting to rewrite the page map.
     hb_vector_t<unsigned> compact_workspace;
     if (unlikely (!allocate_compact_workspace (compact_workspace))) return;

     unsigned int write_index = 0;
     for (unsigned int i = 0; i < page_map.length; i++)
     {
int m = (int) page_map.arrayZ[i].major;
if (m < ds || de < m)
  page_map.arrayZ[write_index++] = page_map.arrayZ[i];
     }
     compact (compact_workspace, write_index);
     resize (write_index);
   }
 }


 public:
 void del_range (hb_codepoint_t a, hb_codepoint_t b)
 {
   if (unlikely (!successful)) return;
   if (unlikely (a > b || a == 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);
   if (!page)
     return false;
   return page->get (g);
 }
 bool may_have (hb_codepoint_t g) const { return get (g); }

 /* Has interface. */
 bool operator [] (hb_codepoint_t k) const { return get (k); }
 bool has (hb_codepoint_t k) const { return (*this)[k]; }
 /* Predicate. */
 bool operator () (hb_codepoint_t k) const { return has (k); }

 /* Sink interface. */
 hb_bit_set_t& operator << (hb_codepoint_t v)
 { add (v); return *this; }
 hb_bit_set_t& operator << (const hb_codepoint_pair_t& range)
 { add_range (range.first, range.second); return *this; }

 bool intersects (const hb_bit_set_t &other) const
 {
   unsigned int na = pages.length;
   unsigned int nb = other.pages.length;

   unsigned int a = 0, b = 0;
   for (; a < na && b < nb; )
   {
     if (page_map.arrayZ[a].major == other.page_map.arrayZ[b].major)
     {
if (page_at (a).intersects (other.page_at (b)))
  return true;
a++;
b++;
     }
     else if (page_map.arrayZ[a].major < other.page_map.arrayZ[b].major)
a++;
     else
b++;
   }
   return false;
 }
 bool may_intersect (const hb_bit_set_t &other) const
 { return intersects (other); }

 bool intersects (hb_codepoint_t first, hb_codepoint_t last) const
 {
   hb_codepoint_t c = first - 1;
   return next (&c) && c <= last;
 }
 void set (const hb_bit_set_t &other, bool exact_size = false)
 {
   if (unlikely (!successful)) return;
   unsigned int count = other.pages.length;
   if (unlikely (!resize  (count, false, exact_size)))
     return;
   population = other.population;

   page_map = other.page_map;
   pages = other.pages;
 }

 bool is_equal (const hb_bit_set_t &other) const
 {
   if (has_population () && other.has_population () &&
population != other.population)
     return false;

   unsigned int na = pages.length;
   unsigned int nb = other.pages.length;

   unsigned int a = 0, b = 0;
   for (; a < na && b < nb; )
   {
     if (page_at (a).is_empty ()) { a++; continue; }
     if (other.page_at (b).is_empty ()) { b++; continue; }
     if (page_map.arrayZ[a].major != other.page_map.arrayZ[b].major ||
  !page_at (a).is_equal (other.page_at (b)))
return false;
     a++;
     b++;
   }
   for (; a < na; a++)
     if (!page_at (a).is_empty ()) { return false; }
   for (; b < nb; b++)
     if (!other.page_at (b).is_empty ()) { return false; }

   return true;
 }

 bool is_subset (const hb_bit_set_t &larger_set) const
 {
   if (has_population () && larger_set.has_population () &&
population > larger_set.population)
     return false;

   uint32_t spi = 0;
   for (uint32_t lpi = 0; spi < page_map.length && lpi < larger_set.page_map.length; lpi++)
   {
     uint32_t spm = page_map.arrayZ[spi].major;
     uint32_t lpm = larger_set.page_map.arrayZ[lpi].major;
     auto sp = page_at (spi);

     if (spm < lpm && !sp.is_empty ())
       return false;

     if (lpm < spm)
       continue;

     auto lp = larger_set.page_at (lpi);
     if (!sp.is_subset (lp))
       return false;

     spi++;
   }

   while (spi < page_map.length)
     if (!page_at (spi++).is_empty ())
       return false;

   return true;
 }

 private:
 bool allocate_compact_workspace (hb_vector_t<unsigned>& workspace)
 {
   if (unlikely (!workspace.resize_exact (pages.length)))
   {
     successful = false;
     return false;
   }

   return true;
 }

 /*
  * workspace should be a pre-sized vector allocated to hold at exactly pages.length
  * elements.
  */
 void compact (hb_vector_t<unsigned>& workspace,
               unsigned int length)
 {
   assert(workspace.length == pages.length);
   hb_vector_t<unsigned>& old_index_to_page_map_index = workspace;

   hb_fill (old_index_to_page_map_index.writer(), 0xFFFFFFFF);
   for (unsigned i = 0; i < length; i++)
     old_index_to_page_map_index[page_map[i].index] =  i;

   compact_pages (old_index_to_page_map_index);
 }
 void compact_pages (const hb_vector_t<unsigned>& old_index_to_page_map_index)
 {
   unsigned int write_index = 0;
   for (unsigned int i = 0; i < pages.length; i++)
   {
     if (old_index_to_page_map_index[i] == 0xFFFFFFFF) continue;

     if (write_index < i)
pages[write_index] = pages[i];

     page_map[old_index_to_page_map_index[i]].index = write_index;
     write_index++;
   }
 }
 public:

 void process_ (hb_bit_page_t::vector_t (*op) (const hb_bit_page_t::vector_t &, const hb_bit_page_t::vector_t &),
	 bool passthru_left, bool passthru_right,
	 const hb_bit_set_t &other)
 {
   if (unlikely (!successful)) return;

   dirty ();

   unsigned int na = pages.length;
   unsigned int nb = other.pages.length;
   unsigned int next_page = na;

   unsigned int count = 0, newCount = 0;
   unsigned int a = 0, b = 0;
   unsigned int write_index = 0;

   // Pre-allocate the workspace that compact() will need so we can bail on allocation failure
   // before attempting to rewrite the page map.
   hb_vector_t<unsigned> compact_workspace;
   if (!passthru_left && unlikely (!allocate_compact_workspace (compact_workspace))) return;

   for (; a < na && b < nb; )
   {
     if (page_map.arrayZ[a].major == other.page_map.arrayZ[b].major)
     {
if (!passthru_left)
{
  // Move page_map entries that we're keeping from the left side set
  // to the front of the page_map vector. This isn't necessary if
  // passthru_left is set since no left side pages will be removed
  // in that case.
  if (write_index < a)
    page_map.arrayZ[write_index] = page_map.arrayZ[a];
  write_index++;
}

count++;
a++;
b++;
     }
     else if (page_map.arrayZ[a].major < other.page_map.arrayZ[b].major)
     {
if (passthru_left)
  count++;
a++;
     }
     else
     {
if (passthru_right)
  count++;
b++;
     }
   }
   if (passthru_left)
     count += na - a;
   if (passthru_right)
     count += nb - b;

   if (!passthru_left)
   {
     na  = write_index;
     next_page = write_index;
     compact (compact_workspace, write_index);
   }

   if (unlikely (!resize (count)))
     return;

   newCount = count;

   /* Process in-place backward. */
   a = na;
   b = nb;
   for (; a && b; )
   {
     if (page_map.arrayZ[a - 1].major == other.page_map.arrayZ[b - 1].major)
     {
a--;
b--;
count--;
page_map.arrayZ[count] = page_map.arrayZ[a];
page_at (count).v = op (page_at (a).v, other.page_at (b).v);
page_at (count).dirty ();
     }
     else if (page_map.arrayZ[a - 1].major > other.page_map.arrayZ[b - 1].major)
     {
a--;
if (passthru_left)
{
  count--;
  page_map.arrayZ[count] = page_map.arrayZ[a];
}
     }
     else
     {
b--;
if (passthru_right)
{
  count--;
  page_map.arrayZ[count].major = other.page_map.arrayZ[b].major;
  page_map.arrayZ[count].index = next_page++;
  page_at (count) = other.page_at (b);
}
     }
   }
   if (passthru_left)
     while (a)
     {
a--;
count--;
page_map.arrayZ[count] = page_map.arrayZ[a];
     }
   if (passthru_right)
     while (b)
     {
b--;
count--;
page_map.arrayZ[count].major = other.page_map.arrayZ[b].major;
page_map.arrayZ[count].index = next_page++;
page_at (count) = other.page_at (b);
     }
   assert (!count);
   resize (newCount);
 }
 template <typename Op>
 static hb_bit_page_t::vector_t
 op_ (const hb_bit_page_t::vector_t &a, const hb_bit_page_t::vector_t &b)
 { return Op{} (a, b); }
 template <typename Op>
 void process (const Op& op, const hb_bit_set_t &other)
 {
   process_ (op_<Op>, op (1, 0), op (0, 1), other);
 }

 void union_ (const hb_bit_set_t &other) { process (hb_bitwise_or, other); }
 void intersect (const hb_bit_set_t &other) { process (hb_bitwise_and, other); }
 void subtract (const hb_bit_set_t &other) { process (hb_bitwise_gt, other); }
 void symmetric_difference (const hb_bit_set_t &other) { process (hb_bitwise_xor, other); }

 bool next (hb_codepoint_t *codepoint) const
 {
   if (unlikely (*codepoint == INVALID)) {
     *codepoint = get_min ();
     return *codepoint != INVALID;
   }

   const auto* page_map_array = page_map.arrayZ;
   unsigned int major = get_major (*codepoint);
   unsigned int i = last_page_lookup;

   if (unlikely (i >= page_map.length || page_map_array[i].major != major))
   {
     page_map.bfind (major, &i, HB_NOT_FOUND_STORE_CLOSEST);
     if (i >= page_map.length) {
       *codepoint = INVALID;
       return false;
     }
     last_page_lookup = i;
   }

   const auto* pages_array = pages.arrayZ;
   const page_map_t &current = page_map_array[i];
   if (likely (current.major == major))
   {
     if (pages_array[current.index].next (codepoint))
     {
       *codepoint += current.major * page_t::PAGE_BITS;
       return true;
     }
     i++;
   }

   for (; i < page_map.length; i++)
   {
     const page_map_t &current = page_map_array[i];
     hb_codepoint_t m = pages_array[current.index].get_min ();
     if (m != INVALID)
     {
*codepoint = current.major * page_t::PAGE_BITS + m;
       last_page_lookup = i;
return true;
     }
   }
   *codepoint = INVALID;
   return false;
 }
 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, HB_NOT_FOUND_STORE_CLOSEST);
   if (i < page_map.length && page_map.arrayZ[i].major == map.major)
   {
     if (pages[page_map.arrayZ[i].index].previous (codepoint))
     {
*codepoint += page_map.arrayZ[i].major * page_t::PAGE_BITS;
return true;
     }
   }
   i--;
   for (; (int) i >= 0; i--)
   {
     hb_codepoint_t m = pages.arrayZ[page_map.arrayZ[i].index].get_max ();
     if (m != INVALID)
     {
*codepoint = page_map.arrayZ[i].major * page_t::PAGE_BITS + m;
return true;
     }
   }
   *codepoint = INVALID;
   return false;
 }
 bool next_range (hb_codepoint_t *first, hb_codepoint_t *last) const
 {
   hb_codepoint_t i;

   i = *last;
   if (!next (&i))
   {
     *last = *first = INVALID;
     return false;
   }

   /* TODO Speed up. */
   *last = *first = i;
   while (next (&i) && i == *last + 1)
     (*last)++;

   return true;
 }
 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;
 }

 unsigned int next_many (hb_codepoint_t  codepoint,
		  hb_codepoint_t *out,
		  unsigned int    size) const
 {
   // By default, start at the first bit of the first page of values.
   unsigned int start_page = 0;
   unsigned int start_page_value = 0;
   if (unlikely (codepoint != INVALID))
   {
     const auto* page_map_array = page_map.arrayZ;
     unsigned int major = get_major (codepoint);
     unsigned int i = last_page_lookup;
     if (unlikely (i >= page_map.length || page_map_array[i].major != major))
     {
page_map.bfind (major, &i, HB_NOT_FOUND_STORE_CLOSEST);
if (i >= page_map.length)
  return 0;  // codepoint is greater than our max element.
     }
     start_page = i;
     start_page_value = page_remainder (codepoint + 1);
     if (unlikely (start_page_value == 0))
     {
       // The export-after value was last in the page. Start on next page.
       start_page++;
       start_page_value = 0;
     }
   }

   unsigned int initial_size = size;
   for (unsigned int i = start_page; i < page_map.length && size; i++)
   {
     uint32_t base = major_start (page_map.arrayZ[i].major);
     unsigned int n = pages[page_map.arrayZ[i].index].write (base, start_page_value, out, size);
     out += n;
     size -= n;
     start_page_value = 0;
   }
   return initial_size - size;
 }

 unsigned int next_many_inverted (hb_codepoint_t  codepoint,
			   hb_codepoint_t *out,
			   unsigned int    size) const
 {
   unsigned int initial_size = size;
   // By default, start at the first bit of the first page of values.
   unsigned int start_page = 0;
   unsigned int start_page_value = 0;
   if (unlikely (codepoint != INVALID))
   {
     const auto* page_map_array = page_map.arrayZ;
     unsigned int major = get_major (codepoint);
     unsigned int i = last_page_lookup;
     if (unlikely (i >= page_map.length || page_map_array[i].major != major))
     {
       page_map.bfind(major, &i, HB_NOT_FOUND_STORE_CLOSEST);
       if (unlikely (i >= page_map.length))
       {
         // codepoint is greater than our max element.
         while (++codepoint != INVALID && size)
         {
           *out++ = codepoint;
           size--;
         }
         return initial_size - size;
       }
     }
     start_page = i;
     start_page_value = page_remainder (codepoint + 1);
     if (unlikely (start_page_value == 0))
     {
       // The export-after value was last in the page. Start on next page.
       start_page++;
       start_page_value = 0;
     }
   }

   hb_codepoint_t next_value = codepoint + 1;
   for (unsigned int i=start_page; i<page_map.length && size; i++)
   {
     uint32_t base = major_start (page_map.arrayZ[i].major);
     unsigned int n = pages[page_map.arrayZ[i].index].write_inverted (base, start_page_value, out, size, &next_value);
     out += n;
     size -= n;
     start_page_value = 0;
   }
   while (next_value < HB_SET_VALUE_INVALID && size) {
     *out++ = next_value++;
     size--;
   }
   return initial_size - size;
 }

 bool has_population () const { return population != UINT_MAX; }
 unsigned int get_population () const
 {
   if (has_population ())
     return population;

   unsigned int pop = 0;
   unsigned int count = pages.length;
   for (unsigned int i = 0; i < count; i++)
     pop += pages[i].get_population ();

   population = pop;
   return pop;
 }
 hb_codepoint_t get_min () const
 {
   unsigned count = pages.length;
   for (unsigned i = 0; i < count; i++)
   {
     const auto& map = page_map.arrayZ[i];
     const auto& page = pages.arrayZ[map.index];

     if (!page.is_empty ())
return map.major * page_t::PAGE_BITS + page.get_min ();
   }
   return INVALID;
 }
 hb_codepoint_t get_max () const
 {
   unsigned count = pages.length;
   for (signed i = count - 1; i >= 0; i--)
   {
     const auto& map = page_map.arrayZ[(unsigned) i];
     const auto& page = pages.arrayZ[map.index];

     if (!page.is_empty ())
return map.major * page_t::PAGE_BITS + page.get_max ();
   }
   return INVALID;
 }

 static constexpr hb_codepoint_t INVALID = page_t::INVALID;

 /*
  * Iterator implementation.
  */
 struct iter_t : hb_iter_with_fallback_t<iter_t, hb_codepoint_t>
 {
   static constexpr bool is_sorted_iterator = true;
   static constexpr bool has_fast_len = true;
   iter_t (const hb_bit_set_t &s_ = Null (hb_bit_set_t),
    bool init = true) : s (&s_), v (INVALID), l(0)
   {
     if (init)
     {
l = s->get_population () + 1;
__next__ ();
     }
   }

   typedef hb_codepoint_t __item_t__;
   hb_codepoint_t __item__ () const { return v; }
   bool __more__ () const { return v != INVALID; }
   void __next__ () { s->next (&v); if (l) l--; }
   void __prev__ () { s->previous (&v); }
   unsigned __len__ () const { return l; }
   iter_t end () const { return iter_t (*s, false); }
   bool operator != (const iter_t& o) const
   { return v != o.v; }

   protected:
   const hb_bit_set_t *s;
   hb_codepoint_t v;
   unsigned l;
 };
 iter_t iter () const { return iter_t (*this); }
 operator iter_t () const { return iter (); }

 protected:

 page_t *page_for (hb_codepoint_t g, bool insert = false)
 {
   unsigned major = get_major (g);

   /* The extra page_map length is necessary; can't just rely on vector here,
    * since the next check would be tricked because a null page also has
    * major==0, which we can't distinguish from an actually major==0 page... */
   unsigned i = last_page_lookup;
   if (likely (i < page_map.length))
   {
     auto &cached_page = page_map.arrayZ[i];
     if (cached_page.major == major)
return &pages.arrayZ[cached_page.index];
   }

   page_map_t map = {major, pages.length};
   if (!page_map.bfind (map, &i, HB_NOT_FOUND_STORE_CLOSEST))
   {
     if (!insert)
       return nullptr;

     if (unlikely (!resize (pages.length + 1)))
return nullptr;

     pages.arrayZ[map.index].init0 ();
     memmove (page_map.arrayZ + i + 1,
       page_map.arrayZ + i,
       (page_map.length - 1 - i) * page_map.item_size);
     page_map.arrayZ[i] = map;
   }

   last_page_lookup = i;
   return &pages.arrayZ[page_map.arrayZ[i].index];
 }
 const page_t *page_for (hb_codepoint_t g) const
 {
   unsigned major = get_major (g);

   /* The extra page_map length is necessary; can't just rely on vector here,
    * since the next check would be tricked because a null page also has
    * major==0, which we can't distinguish from an actually major==0 page... */
   unsigned i = last_page_lookup;
   if (likely (i < page_map.length))
   {
     auto &cached_page = page_map.arrayZ[i];
     if (cached_page.major == major)
return &pages.arrayZ[cached_page.index];
   }

   page_map_t key = {major};
   if (!page_map.bfind (key, &i))
     return nullptr;

   last_page_lookup = i;
   return &pages.arrayZ[page_map.arrayZ[i].index];
 }
 page_t &page_at (unsigned int i)
 {
   assert (i < page_map.length);
   return pages.arrayZ[page_map.arrayZ[i].index];
 }
 const page_t &page_at (unsigned int i) const
 {
   assert (i < page_map.length);
   return pages.arrayZ[page_map.arrayZ[i].index];
 }
 unsigned int get_major (hb_codepoint_t g) const { return g >> page_t::PAGE_BITS_LOG_2; }
 unsigned int page_remainder (hb_codepoint_t g) const { return g & page_t::PAGE_BITMASK; }
 hb_codepoint_t major_start (unsigned int major) const { return major << page_t::PAGE_BITS_LOG_2; }
};


#endif /* HB_BIT_SET_HH */