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#pragma once
#include "base/assert.hpp"
#include "base/base.hpp"
#include "base/macros.hpp"
#include <memory>
#include <type_traits>
#include <utility>
namespace base
{
// Simple cache that stores list of values.
template <typename KeyT, typename ValueT> class Cache
{
DISALLOW_COPY(Cache);
public:
Cache() = default;
Cache(Cache && r) = default;
/// @param[in] logCacheSize is pow of two for number of elements in cache.
explicit Cache(uint32_t logCacheSize)
{
Init(logCacheSize);
}
/// @param[in] logCacheSize is pow of two for number of elements in cache.
void Init(uint32_t logCacheSize)
{
ASSERT(logCacheSize > 0 && logCacheSize < 32, (logCacheSize));
static_assert((std::is_same<KeyT, uint32_t>::value || std::is_same<KeyT, uint64_t>::value), "");
m_cache.reset(new Data[1 << logCacheSize]);
m_hashMask = (1 << logCacheSize) - 1;
Reset();
}
uint32_t GetCacheSize() const
{
return m_hashMask + 1;
}
// Find value by @key. If @key is found, returns reference to its value.
// If @key is not found, some other key is removed and it's value is reused without
// re-initialization. It's up to caller to re-initialize the new value if @found == false.
// TODO: Return pair<ValueT *, bool> instead?
ValueT & Find(KeyT const & key, bool & found)
{
Data & data = m_cache[Index(key)];
if (data.m_Key == key)
{
found = true;
}
else
{
found = false;
data.m_Key = key;
}
return data.m_Value;
}
template <typename F>
void ForEachValue(F && f)
{
for (uint32_t i = 0; i <= m_hashMask; ++i)
f(m_cache[i].m_Value);
}
void Reset()
{
// Initialize m_Cache such, that Index(m_Cache[i].m_Key) != i.
for (uint32_t i = 0; i <= m_hashMask; ++i)
{
KeyT & key = m_cache[i].m_Key;
for (key = 0; Index(key) == i; ++key) ;
}
}
private:
inline size_t Index(KeyT const & key) const
{
return static_cast<size_t>(Hash(key) & m_hashMask);
}
inline static uint32_t Hash(uint32_t x)
{
x = (x ^ 61) ^ (x >> 16);
x = x + (x << 3);
x = x ^ (x >> 4);
x = x * 0x27d4eb2d;
x = x ^ (x >> 15);
return x;
}
inline static uint32_t Hash(uint64_t x)
{
return Hash(uint32_t(x) ^ uint32_t(x >> 32));
}
// TODO: Consider using separate arrays for keys and values, to save on padding.
struct Data
{
Data() : m_Key(), m_Value() {}
KeyT m_Key;
ValueT m_Value;
};
std::unique_ptr<Data[]> m_cache;
uint32_t m_hashMask;
};
// Simple cache that stores list of values and provides cache missing statistics.
// CacheWithStat class has the same interface as Cache class
template <typename TKey, typename TValue>
class CacheWithStat
{
public:
CacheWithStat() = default;
explicit CacheWithStat(uint32_t logCacheSize)
: m_cache(logCacheSize), m_miss(0), m_access(0)
{
}
/// @param[in] logCacheSize is pow of two for number of elements in cache.
void Init(uint32_t logCacheSize)
{
m_cache.Init(logCacheSize);
m_miss = m_access = 0;
}
double GetCacheMiss() const
{
if (m_access == 0)
return 0.0;
return static_cast<double>(m_miss) / static_cast<double>(m_access);
}
uint32_t GetCacheSize() const { return m_cache.GetCacheSize(); }
TValue & Find(TKey const & key, bool & found)
{
++m_access;
TValue & res = m_cache.Find(key, found);
if (!found)
++m_miss;
return res;
}
template <typename F>
void ForEachValue(F && f)
{
m_cache.ForEachValue(std::forward<F>(f));
}
void Reset()
{
m_cache.Reset();
m_access = 0;
m_miss = 0;
}
private:
Cache<TKey, TValue> m_cache;
uint64_t m_miss;
uint64_t m_access;
};
} // namespace base
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