227 lines
6.9 KiB
C++
227 lines
6.9 KiB
C++
/*
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* Copyright © 2012 Google, Inc.
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*
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* This is part of HarfBuzz, a text shaping library.
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*
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* Permission is hereby granted, without written agreement and without
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* license or royalty fees, to use, copy, modify, and distribute this
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* software and its documentation for any purpose, provided that the
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* above copyright notice and the following two paragraphs appear in
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* all copies of this software.
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*
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* IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
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* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
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* ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
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* IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
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* DAMAGE.
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*
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* THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
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* BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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* FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
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* ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
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* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
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*
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* Google Author(s): Behdad Esfahbod
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*/
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#ifndef HB_SET_DIGEST_HH
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#define HB_SET_DIGEST_HH
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#include "hb.hh"
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#include "hb-machinery.hh"
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/*
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* The set-digests here implement various "filters" that support
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* "approximate member query". Conceptually these are like Bloom
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* Filter and Quotient Filter, however, much smaller, faster, and
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* designed to fit the requirements of our uses for glyph coverage
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* queries.
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*
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* Our filters are highly accurate if the lookup covers fairly local
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* set of glyphs, but fully flooded and ineffective if coverage is
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* all over the place.
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*
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* The way these are used is that the filter is first populated by
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* a lookup's or subtable's Coverage table(s), and then when we
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* want to apply the lookup or subtable to a glyph, before trying
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* to apply, we ask the filter if the glyph may be covered. If it's
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* not, we return early. We can also match a digest against another
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* digest.
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*
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* We use these filters at three levels:
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* - If the digest for all the glyphs in the buffer as a whole
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* does not match the digest for the lookup, skip the lookup.
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* - For each glyph, if it doesn't match the lookup digest,
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* skip it.
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* - For each glyph, if it doesn't match the subtable digest,
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* skip it.
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*
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* The main filter we use is a combination of three bits-pattern
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* filters. A bits-pattern filter checks a number of bits (5 or 6)
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* of the input number (glyph-id in this case) and checks whether
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* its pattern is amongst the patterns of any of the accepted values.
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* The accepted patterns are represented as a "long" integer. The
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* check is done using four bitwise operations only.
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*/
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template <typename mask_t, unsigned int shift>
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struct hb_set_digest_bits_pattern_t
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{
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static constexpr unsigned mask_bytes = sizeof (mask_t);
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static constexpr unsigned mask_bits = sizeof (mask_t) * 8;
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static constexpr unsigned num_bits = 0
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+ (mask_bytes >= 1 ? 3 : 0)
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+ (mask_bytes >= 2 ? 1 : 0)
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+ (mask_bytes >= 4 ? 1 : 0)
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+ (mask_bytes >= 8 ? 1 : 0)
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+ (mask_bytes >= 16? 1 : 0)
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+ 0;
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static_assert ((shift < sizeof (hb_codepoint_t) * 8), "");
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static_assert ((shift + num_bits <= sizeof (hb_codepoint_t) * 8), "");
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void init () { mask = 0; }
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static hb_set_digest_bits_pattern_t full () { hb_set_digest_bits_pattern_t d; d.mask = (mask_t) -1; return d; }
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void union_ (const hb_set_digest_bits_pattern_t &o) { mask |= o.mask; }
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void add (hb_codepoint_t g) { mask |= mask_for (g); }
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bool add_range (hb_codepoint_t a, hb_codepoint_t b)
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{
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if (mask == (mask_t) -1) return false;
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if ((b >> shift) - (a >> shift) >= mask_bits - 1)
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{
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mask = (mask_t) -1;
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return false;
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}
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else
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{
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mask_t ma = mask_for (a);
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mask_t mb = mask_for (b);
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mask |= mb + (mb - ma) - (mb < ma);
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return true;
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}
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}
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template <typename T>
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void add_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
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{
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for (unsigned int i = 0; i < count; i++)
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{
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add (*array);
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array = &StructAtOffsetUnaligned<T> ((const void *) array, stride);
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}
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}
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template <typename T>
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void add_array (const hb_array_t<const T>& arr) { add_array (&arr, arr.len ()); }
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template <typename T>
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bool add_sorted_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
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{
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add_array (array, count, stride);
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return true;
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}
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template <typename T>
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bool add_sorted_array (const hb_sorted_array_t<const T>& arr) { return add_sorted_array (&arr, arr.len ()); }
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bool may_have (const hb_set_digest_bits_pattern_t &o) const
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{ return mask & o.mask; }
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bool may_have (hb_codepoint_t g) const
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{ return mask & mask_for (g); }
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bool operator [] (hb_codepoint_t g) const
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{ return may_have (g); }
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private:
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static mask_t mask_for (hb_codepoint_t g)
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{ return ((mask_t) 1) << ((g >> shift) & (mask_bits - 1)); }
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mask_t mask = 0;
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};
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template <typename head_t, typename tail_t>
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struct hb_set_digest_combiner_t
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{
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void init ()
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{
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head.init ();
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tail.init ();
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}
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static hb_set_digest_combiner_t full () { hb_set_digest_combiner_t d; d.head = head_t::full(); d.tail = tail_t::full (); return d; }
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void union_ (const hb_set_digest_combiner_t &o)
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{
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head.union_ (o.head);
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tail.union_(o.tail);
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}
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void add (hb_codepoint_t g)
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{
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head.add (g);
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tail.add (g);
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}
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bool add_range (hb_codepoint_t a, hb_codepoint_t b)
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{
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return (int) head.add_range (a, b) | (int) tail.add_range (a, b);
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}
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template <typename T>
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void add_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
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{
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head.add_array (array, count, stride);
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tail.add_array (array, count, stride);
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}
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template <typename T>
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void add_array (const hb_array_t<const T>& arr) { add_array (&arr, arr.len ()); }
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template <typename T>
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bool add_sorted_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
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{
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return head.add_sorted_array (array, count, stride) &&
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tail.add_sorted_array (array, count, stride);
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}
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template <typename T>
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bool add_sorted_array (const hb_sorted_array_t<const T>& arr) { return add_sorted_array (&arr, arr.len ()); }
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bool may_have (const hb_set_digest_combiner_t &o) const
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{
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return head.may_have (o.head) && tail.may_have (o.tail);
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}
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bool may_have (hb_codepoint_t g) const
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{
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return head.may_have (g) && tail.may_have (g);
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}
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bool operator [] (hb_codepoint_t g) const
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{ return may_have (g); }
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private:
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head_t head;
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tail_t tail;
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};
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/*
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* hb_set_digest_t
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*
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* This is a combination of digests that performs "best".
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* There is not much science to this: it's a result of intuition
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* and testing.
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*/
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using hb_set_digest_t =
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hb_set_digest_combiner_t
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<
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hb_set_digest_bits_pattern_t<unsigned long, 4>,
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hb_set_digest_combiner_t
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<
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hb_set_digest_bits_pattern_t<unsigned long, 0>,
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hb_set_digest_bits_pattern_t<unsigned long, 9>
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>
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>
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;
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#endif /* HB_SET_DIGEST_HH */
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