LruCounter.hxx

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#ifndef _UTILS_LRUCOUNTER_HXX_
#define _UTILS_LRUCOUNTER_HXX_
 
#include <limits>
 
template <class T> class LruCounter;
 
class GlobalLruCounter
{
public:
    GlobalLruCounter(unsigned bits_per_bit = 2)
        : bitsPerBit_(bits_per_bit)
    {
    }
    void tick()
    {
        ++tick_;
    }
 
private:
    template <class T> friend class LruCounter;
    unsigned bitsPerBit_;
    unsigned tick_ {0};
};
 
template <class T> class LruCounter
{
public:
    unsigned value()
    {
        return counter_;
    }
 
    void tick(const GlobalLruCounter &global)
    {
        if (!counter_)
        {
            ++counter_;
            return;
        }
        if (counter_ == std::numeric_limits<T>::max())
        {
            // Counter is saturated.
            return;
        }
        int nlz = __builtin_clz((unsigned)counter_);
        int needzero = (32 - nlz) * global.bitsPerBit_;
        if ((global.tick_ & ((1U << needzero) - 1)) == 0)
        {
            ++counter_;
        }
    }
 
    void touch()
    {
        counter_ = 0;
    }
 
private:
    T counter_ {0};
};
 
#endif // _UTILS_LRUCOUNTER_HXX_