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/*
* 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_CACHE_HH
#define HB_CACHE_HH
#include "hb.hh"
/* Implements a lockfree cache for int->int functions.
*
* The cache is a fixed-size array of 16-bit or 32-bit integers.
* The key is split into two parts: the cache index and the rest.
*
* The cache index is used to index into the array. The rest is used
* to store the key and the value.
*
* The value is stored in the least significant bits of the integer.
* The key is stored in the most significant bits of the integer.
* The key is shifted by cache_bits to the left to make room for the
* value.
*/
template <unsigned int key_bits=16,
unsigned int value_bits=8 + 32 - key_bits,
unsigned int cache_bits=8,
bool thread_safe=true>
struct hb_cache_t
{
using item_t = typename std::conditional<thread_safe,
typename std::conditional<key_bits + value_bits - cache_bits <= 16,
hb_atomic_short_t,
hb_atomic_int_t>::type,
typename std::conditional<key_bits + value_bits - cache_bits <= 16,
short,
int>::type
>::type;
static_assert ((key_bits >= cache_bits), "");
static_assert ((key_bits + value_bits <= cache_bits + 8 * sizeof (item_t)), "");
hb_cache_t () { clear (); }
void clear ()
{
for (auto &v : values)
v = -1;
}
bool get (unsigned int key, unsigned int *value) const
{
unsigned int k = key & ((1u<<cache_bits)-1);
unsigned int v = values[k];
if ((key_bits + value_bits - cache_bits == 8 * sizeof (item_t) && v == (unsigned int) -1) ||
(v >> value_bits) != (key >> cache_bits))
return false;
*value = v & ((1u<<value_bits)-1);
return true;
}
bool set (unsigned int key, unsigned int value)
{
if (unlikely ((key >> key_bits) || (value >> value_bits)))
return false; /* Overflows */
unsigned int k = key & ((1u<<cache_bits)-1);
unsigned int v = ((key>>cache_bits)<<value_bits) | value;
values[k] = v;
return true;
}
private:
item_t values[1u<<cache_bits];
};
#endif /* HB_CACHE_HH */
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