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#ifndef UTIL_PROBING_HASH_TABLE__
#define UTIL_PROBING_HASH_TABLE__
#include "util/exception.hh"
#include <algorithm>
#include <cstddef>
#include <functional>
#include <assert.h>
namespace util {
/* Thrown when table grows too large */
class ProbingSizeException : public Exception {
public:
ProbingSizeException() throw() {}
~ProbingSizeException() throw() {}
};
/* Non-standard hash table
* Buckets must be set at the beginning and must be greater than maximum number
* of elements, else an infinite loop happens.
* Memory management and initialization is externalized to make it easier to
* serialize these to disk and load them quickly.
* Uses linear probing to find value.
* Only insert and lookup operations.
*/
template <class PackingT, class HashT, class EqualT = std::equal_to<typename PackingT::Key> > class ProbingHashTable {
public:
typedef PackingT Packing;
typedef typename Packing::Key Key;
typedef typename Packing::MutableIterator MutableIterator;
typedef typename Packing::ConstIterator ConstIterator;
typedef HashT Hash;
typedef EqualT Equal;
static std::size_t Size(std::size_t entries, float multiplier) {
return std::max(entries + 1, static_cast<std::size_t>(multiplier * static_cast<float>(entries))) * Packing::kBytes;
}
// Must be assigned to later.
ProbingHashTable() : entries_(0)
#ifdef DEBUG
, initialized_(false)
#endif
{}
ProbingHashTable(void *start, std::size_t allocated, const Key &invalid = Key(), const Hash &hash_func = Hash(), const Equal &equal_func = Equal())
: begin_(Packing::FromVoid(start)),
buckets_(allocated / Packing::kBytes),
end_(begin_ + (allocated / Packing::kBytes)),
invalid_(invalid),
hash_(hash_func),
equal_(equal_func),
entries_(0)
#ifdef DEBUG
, initialized_(true),
#endif
{}
template <class T> void Insert(const T &t) {
if (++entries_ >= buckets_)
UTIL_THROW(ProbingSizeException, "Hash table with " << buckets_ << " buckets is full.");
#ifdef DEBUG
assert(initialized_);
#endif
for (MutableIterator i(begin_ + (hash_(t.GetKey()) % buckets_));;) {
if (equal_(i->GetKey(), invalid_)) { *i = t; return; }
if (++i == end_) { i = begin_; }
}
}
void FinishedInserting() {}
void LoadedBinary() {}
template <class Key> bool Find(const Key key, ConstIterator &out) const {
#ifdef DEBUG
assert(initialized_);
#endif
for (ConstIterator i(begin_ + (hash_(key) % buckets_));;) {
Key got(i->GetKey());
if (equal_(got, key)) { out = i; return true; }
if (equal_(got, invalid_)) { return false; }
if (++i == end_) { i = begin_; }
}
}
private:
MutableIterator begin_;
std::size_t buckets_;
MutableIterator end_;
Key invalid_;
Hash hash_;
Equal equal_;
std::size_t entries_;
#ifdef DEBUG
bool initialized_;
#endif
};
} // namespace util
#endif // UTIL_PROBING_HASH_TABLE__
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