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Diffstat (limited to '')
| -rw-r--r-- | gfx/harfbuzz/src/hb-set-digest.hh | 174 |
1 files changed, 174 insertions, 0 deletions
diff --git a/gfx/harfbuzz/src/hb-set-digest.hh b/gfx/harfbuzz/src/hb-set-digest.hh new file mode 100644 index 0000000000..b97526f775 --- /dev/null +++ b/gfx/harfbuzz/src/hb-set-digest.hh @@ -0,0 +1,174 @@ +/* + * Copyright © 2012 Google, Inc. + * + * 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_SET_DIGEST_HH +#define HB_SET_DIGEST_HH + +#include "hb.hh" + +/* + * The set digests here implement various "filters" that support + * "approximate member query". Conceptually these are like Bloom + * Filter and Quotient Filter, however, much smaller, faster, and + * designed to fit the requirements of our uses for glyph coverage + * queries. + * + * Our filters are highly accurate if the lookup covers fairly local + * set of glyphs, but fully flooded and ineffective if coverage is + * all over the place. + * + * The frozen-set can be used instead of a digest, to trade more + * memory for 100% accuracy, but in practice, that doesn't look like + * an attractive trade-off. + */ + +template <typename mask_t, unsigned int shift> +struct hb_set_digest_lowest_bits_t +{ + static constexpr unsigned mask_bytes = sizeof (mask_t); + static constexpr unsigned mask_bits = sizeof (mask_t) * 8; + static constexpr unsigned num_bits = 0 + + (mask_bytes >= 1 ? 3 : 0) + + (mask_bytes >= 2 ? 1 : 0) + + (mask_bytes >= 4 ? 1 : 0) + + (mask_bytes >= 8 ? 1 : 0) + + (mask_bytes >= 16? 1 : 0) + + 0; + + static_assert ((shift < sizeof (hb_codepoint_t) * 8), ""); + static_assert ((shift + num_bits <= sizeof (hb_codepoint_t) * 8), ""); + + void init () { mask = 0; } + + void add (hb_codepoint_t g) { mask |= mask_for (g); } + + bool add_range (hb_codepoint_t a, hb_codepoint_t b) + { + if ((b >> shift) - (a >> shift) >= mask_bits - 1) + mask = (mask_t) -1; + else { + mask_t ma = mask_for (a); + mask_t mb = mask_for (b); + mask |= mb + (mb - ma) - (mb < ma); + } + return true; + } + + template <typename T> + void add_array (const T *array, unsigned int count, unsigned int stride=sizeof(T)) + { + for (unsigned int i = 0; i < count; i++) + { + add (*array); + array = (const T *) (stride + (const char *) array); + } + } + template <typename T> + bool add_sorted_array (const T *array, unsigned int count, unsigned int stride=sizeof(T)) + { + for (unsigned int i = 0; i < count; i++) + { + add (*array); + array = (const T *) (stride + (const char *) array); + } + return true; + } + + bool may_have (hb_codepoint_t g) const + { return !!(mask & mask_for (g)); } + + private: + + static mask_t mask_for (hb_codepoint_t g) + { return ((mask_t) 1) << ((g >> shift) & (mask_bits - 1)); } + mask_t mask; +}; + +template <typename head_t, typename tail_t> +struct hb_set_digest_combiner_t +{ + void init () + { + head.init (); + tail.init (); + } + + void add (hb_codepoint_t g) + { + head.add (g); + tail.add (g); + } + + bool add_range (hb_codepoint_t a, hb_codepoint_t b) + { + head.add_range (a, b); + tail.add_range (a, b); + return true; + } + template <typename T> + void add_array (const T *array, unsigned int count, unsigned int stride=sizeof(T)) + { + head.add_array (array, count, stride); + tail.add_array (array, count, stride); + } + template <typename T> + bool add_sorted_array (const T *array, unsigned int count, unsigned int stride=sizeof(T)) + { + head.add_sorted_array (array, count, stride); + tail.add_sorted_array (array, count, stride); + return true; + } + + bool may_have (hb_codepoint_t g) const + { + return head.may_have (g) && tail.may_have (g); + } + + private: + head_t head; + tail_t tail; +}; + + +/* + * hb_set_digest_t + * + * This is a combination of digests that performs "best". + * There is not much science to this: it's a result of intuition + * and testing. + */ +typedef hb_set_digest_combiner_t +< + hb_set_digest_lowest_bits_t<unsigned long, 4>, + hb_set_digest_combiner_t + < + hb_set_digest_lowest_bits_t<unsigned long, 0>, + hb_set_digest_lowest_bits_t<unsigned long, 9> + > +> hb_set_digest_t; + + +#endif /* HB_SET_DIGEST_HH */ |