PoolHelper.h

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#pragma once
 
#include <algorithm>
#include <cmath>
#include <cstddef>
#include <utility>
 
namespace carl {
namespace pool {
 
/**
 * Mimics stdlibs default rehash policy for hashtables.
 * See https://gcc.gnu.org/onlinedocs/libstdc++/libstdc++-html-USERS-4.1/hashtable-source.html
 */
class RehashPolicy {
    static const int numPrimes = sizeof(unsigned long) != 8 ? 256 : 256 + 48;
    static const unsigned long primes[256 + 48 + 1];
 
    float mMaxLoadFactor; // stdlib uses 1
    float mGrowthFactor; // stdlib uses 2
    mutable std::size_t mNextResize;
 
public:
    RehashPolicy(float maxLoadFactor = 0.95f, float growthFactor = 2.f)
        : mMaxLoadFactor(maxLoadFactor), mGrowthFactor(growthFactor), mNextResize(0) {}
 
    std::size_t numBucketsFor(std::size_t numElements) const;
    std::pair<bool, std::size_t> needRehash(std::size_t numBuckets, std::size_t numElements) const;
};
 
} // namespace pool
} // namespace carl