Behdad Esfahbod
7 years ago
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3c13e153fe
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826a1daf2f
4 changed files with 146 additions and 114 deletions
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/*
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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_PRIVATE_HH |
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#define HB_SET_DIGEST_PRIVATE_HH |
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#include "hb-private.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 frozen-set can be used instead of a digest, to trade more |
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* memory for 100% accuracy, but in practice, that doesn't look like |
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* an attractive trade-off. |
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*/ |
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template <typename mask_t, unsigned int shift> |
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struct hb_set_digest_lowest_bits_t |
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{ |
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ASSERT_POD (); |
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static const unsigned int mask_bytes = sizeof (mask_t); |
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static const unsigned int mask_bits = sizeof (mask_t) * 8; |
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static const unsigned int 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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inline void init (void) { |
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mask = 0; |
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} |
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inline void add (hb_codepoint_t g) { |
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mask |= mask_for (g); |
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} |
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inline void add_range (hb_codepoint_t a, hb_codepoint_t b) { |
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if ((b >> shift) - (a >> shift) >= mask_bits - 1) |
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mask = (mask_t) -1; |
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else { |
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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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} |
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} |
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inline bool may_have (hb_codepoint_t g) const { |
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return !!(mask & mask_for (g)); |
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} |
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private: |
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static inline 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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} |
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mask_t mask; |
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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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ASSERT_POD (); |
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inline void init (void) { |
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head.init (); |
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tail.init (); |
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} |
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inline void add (hb_codepoint_t g) { |
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head.add (g); |
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tail.add (g); |
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} |
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inline void add_range (hb_codepoint_t a, hb_codepoint_t b) { |
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head.add_range (a, b); |
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tail.add_range (a, b); |
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} |
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inline bool may_have (hb_codepoint_t g) const { |
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return head.may_have (g) && tail.may_have (g); |
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} |
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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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typedef hb_set_digest_combiner_t |
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< |
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hb_set_digest_lowest_bits_t<unsigned long, 4>, |
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hb_set_digest_combiner_t |
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< |
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hb_set_digest_lowest_bits_t<unsigned long, 0>, |
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hb_set_digest_lowest_bits_t<unsigned long, 9> |
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> |
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> hb_set_digest_t; |
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#endif /* HB_SET_DIGEST_PRIVATE_HH */ |
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