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#ifndef LM_BUILDER_SORT_H
#define LM_BUILDER_SORT_H
#include "lm/builder/ngram_stream.hh"
#include "lm/builder/ngram.hh"
#include "lm/word_index.hh"
#include "util/stream/sort.hh"
#include "util/stream/timer.hh"
#include <functional>
#include <string>
namespace lm {
namespace builder {
/**
* Abstract parent class for defining custom n-gram comparators.
*/
template <class Child> class Comparator : public std::binary_function<const void *, const void *, bool> {
public:
/**
* Constructs a comparator capable of comparing two n-grams.
*
* @param order Number of words in each n-gram
*/
explicit Comparator(std::size_t order) : order_(order) {}
/**
* Applies the comparator using the Compare method that must be defined in any class that inherits from this class.
*
* @param lhs A pointer to the n-gram on the left-hand side of the comparison
* @param rhs A pointer to the n-gram on the right-hand side of the comparison
*
* @see ContextOrder::Compare
* @see PrefixOrder::Compare
* @see SuffixOrder::Compare
*/
inline bool operator()(const void *lhs, const void *rhs) const {
return static_cast<const Child*>(this)->Compare(static_cast<const WordIndex*>(lhs), static_cast<const WordIndex*>(rhs));
}
/** Gets the n-gram order defined for this comparator. */
std::size_t Order() const { return order_; }
protected:
std::size_t order_;
};
/**
* N-gram comparator that compares n-grams according to their reverse (suffix) order.
*
* This comparator compares n-grams lexicographically, one word at a time,
* beginning with the last word of each n-gram and ending with the first word of each n-gram.
*
* Some examples of n-gram comparisons as defined by this comparator:
* - a b c == a b c
* - a b c < a b d
* - a b c > a d b
* - a b c > a b b
* - a b c > x a c
* - a b c < x y z
*/
class SuffixOrder : public Comparator<SuffixOrder> {
public:
/**
* Constructs a comparator capable of comparing two n-grams.
*
* @param order Number of words in each n-gram
*/
explicit SuffixOrder(std::size_t order) : Comparator<SuffixOrder>(order) {}
/**
* Compares two n-grams lexicographically, one word at a time,
* beginning with the last word of each n-gram and ending with the first word of each n-gram.
*
* @param lhs A pointer to the n-gram on the left-hand side of the comparison
* @param rhs A pointer to the n-gram on the right-hand side of the comparison
*/
inline bool Compare(const WordIndex *lhs, const WordIndex *rhs) const {
for (std::size_t i = order_ - 1; i != 0; --i) {
if (lhs[i] != rhs[i])
return lhs[i] < rhs[i];
}
return lhs[0] < rhs[0];
}
static const unsigned kMatchOffset = 1;
};
/**
* N-gram comparator that compares n-grams according to the reverse (suffix) order of the n-gram context.
*
* This comparator compares n-grams lexicographically, one word at a time,
* beginning with the penultimate word of each n-gram and ending with the first word of each n-gram;
* finally, this comparator compares the last word of each n-gram.
*
* Some examples of n-gram comparisons as defined by this comparator:
* - a b c == a b c
* - a b c < a b d
* - a b c < a d b
* - a b c > a b b
* - a b c > x a c
* - a b c < x y z
*/
class ContextOrder : public Comparator<ContextOrder> {
public:
/**
* Constructs a comparator capable of comparing two n-grams.
*
* @param order Number of words in each n-gram
*/
explicit ContextOrder(std::size_t order) : Comparator<ContextOrder>(order) {}
/**
* Compares two n-grams lexicographically, one word at a time,
* beginning with the penultimate word of each n-gram and ending with the first word of each n-gram;
* finally, this comparator compares the last word of each n-gram.
*
* @param lhs A pointer to the n-gram on the left-hand side of the comparison
* @param rhs A pointer to the n-gram on the right-hand side of the comparison
*/
inline bool Compare(const WordIndex *lhs, const WordIndex *rhs) const {
for (int i = order_ - 2; i >= 0; --i) {
if (lhs[i] != rhs[i])
return lhs[i] < rhs[i];
}
return lhs[order_ - 1] < rhs[order_ - 1];
}
};
/**
* N-gram comparator that compares n-grams according to their natural (prefix) order.
*
* This comparator compares n-grams lexicographically, one word at a time,
* beginning with the first word of each n-gram and ending with the last word of each n-gram.
*
* Some examples of n-gram comparisons as defined by this comparator:
* - a b c == a b c
* - a b c < a b d
* - a b c < a d b
* - a b c > a b b
* - a b c < x a c
* - a b c < x y z
*/
class PrefixOrder : public Comparator<PrefixOrder> {
public:
/**
* Constructs a comparator capable of comparing two n-grams.
*
* @param order Number of words in each n-gram
*/
explicit PrefixOrder(std::size_t order) : Comparator<PrefixOrder>(order) {}
/**
* Compares two n-grams lexicographically, one word at a time,
* beginning with the first word of each n-gram and ending with the last word of each n-gram.
*
* @param lhs A pointer to the n-gram on the left-hand side of the comparison
* @param rhs A pointer to the n-gram on the right-hand side of the comparison
*/
inline bool Compare(const WordIndex *lhs, const WordIndex *rhs) const {
for (std::size_t i = 0; i < order_; ++i) {
if (lhs[i] != rhs[i])
return lhs[i] < rhs[i];
}
return false;
}
static const unsigned kMatchOffset = 0;
};
// Sum counts for the same n-gram.
struct AddCombiner {
bool operator()(void *first_void, const void *second_void, const SuffixOrder &compare) const {
NGram first(first_void, compare.Order());
// There isn't a const version of NGram.
NGram second(const_cast<void*>(second_void), compare.Order());
if (memcmp(first.begin(), second.begin(), sizeof(WordIndex) * compare.Order())) return false;
first.Count() += second.Count();
return true;
}
};
// The combiner is only used on a single chain, so I didn't bother to allow
// that template.
/**
* Represents an @ref util::FixedArray "array" capable of storing @ref util::stream::Sort "Sort" objects.
*
* In the anticipated use case, an instance of this class will maintain one @ref util::stream::Sort "Sort" object
* for each n-gram order (ranging from 1 up to the maximum n-gram order being processed).
* Use in this manner would enable the n-grams each n-gram order to be sorted, in parallel.
*
* @tparam Compare An @ref Comparator "ngram comparator" to use during sorting.
*/
template <class Compare> class Sorts : public util::FixedArray<util::stream::Sort<Compare> > {
private:
typedef util::stream::Sort<Compare> S;
typedef util::FixedArray<S> P;
public:
/**
* Constructs, but does not initialize.
*
* @ref util::FixedArray::Init() "Init" must be called before use.
*
* @see util::FixedArray::Init()
*/
Sorts() {}
/**
* Constructs an @ref util::FixedArray "array" capable of storing a fixed number of @ref util::stream::Sort "Sort" objects.
*
* @param number The maximum number of @ref util::stream::Sort "sorters" that can be held by this @ref util::FixedArray "array"
* @see util::FixedArray::FixedArray()
*/
explicit Sorts(std::size_t number) : util::FixedArray<util::stream::Sort<Compare> >(number) {}
/**
* Constructs a new @ref util::stream::Sort "Sort" object which is stored in this @ref util::FixedArray "array".
*
* The new @ref util::stream::Sort "Sort" object is constructed using the provided @ref util::stream::SortConfig "SortConfig" and @ref Comparator "ngram comparator";
* once constructed, a new worker @ref util::stream::Thread "thread" (owned by the @ref util::stream::Chain "chain") will sort the n-gram data stored
* in the @ref util::stream::Block "blocks" of the provided @ref util::stream::Chain "chain".
*
* @see util::stream::Sort::Sort()
* @see util::stream::Chain::operator>>()
*/
void push_back(util::stream::Chain &chain, const util::stream::SortConfig &config, const Compare &compare) {
new (P::end()) S(chain, config, compare); // use "placement new" syntax to initalize S in an already-allocated memory location
P::Constructed();
}
};
} // namespace builder
} // namespace lm
#endif // LM_BUILDER_SORT_H
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