1 /*
2  * Copyright © 2012  Google, Inc.
3  *
4  *  This is part of HarfBuzz, a text shaping library.
5  *
6  * Permission is hereby granted, without written agreement and without
7  * license or royalty fees, to use, copy, modify, and distribute this
8  * software and its documentation for any purpose, provided that the
9  * above copyright notice and the following two paragraphs appear in
10  * all copies of this software.
11  *
12  * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
13  * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
14  * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
15  * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
16  * DAMAGE.
17  *
18  * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
19  * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
20  * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
21  * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
22  * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
23  *
24  * Google Author(s): Behdad Esfahbod
25  */
26 
27 #ifndef HB_CACHE_PRIVATE_HH
28 #define HB_CACHE_PRIVATE_HH
29 
30 #include "hb-private.hh"
31 
32 
33 /* Implements a lock-free cache for int->int functions. */
34 
35 template <unsigned int key_bits, unsigned int value_bits, unsigned int cache_bits>
36 struct hb_cache_t
37 {
38   ASSERT_STATIC (key_bits >= cache_bits);
39   ASSERT_STATIC (key_bits + value_bits - cache_bits < 8 * sizeof (unsigned int));
40 
clearhb_cache_t41   inline void clear (void)
42   {
43     memset (values, 255, sizeof (values));
44   }
45 
gethb_cache_t46   inline bool get (unsigned int key, unsigned int *value)
47   {
48     unsigned int k = key & ((1<<cache_bits)-1);
49     unsigned int v = values[k];
50     if ((v >> value_bits) != (key >> cache_bits))
51       return false;
52     *value = v & ((1<<value_bits)-1);
53     return true;
54   }
55 
sethb_cache_t56   inline bool set (unsigned int key, unsigned int value)
57   {
58     if (unlikely ((key >> key_bits) || (value >> value_bits)))
59       return false; /* Overflows */
60     unsigned int k = key & ((1<<cache_bits)-1);
61     unsigned int v = ((key>>cache_bits)<<value_bits) | value;
62     values[k] = v;
63     return true;
64   }
65 
66   private:
67   unsigned int values[1<<cache_bits];
68 };
69 
70 typedef hb_cache_t<21, 16, 8> hb_cmap_cache_t;
71 typedef hb_cache_t<16, 24, 8> hb_advance_cache_t;
72 
73 
74 #endif /* HB_CACHE_PRIVATE_HH */
75