mosesdecoder/lm/trie.cc

#include "lm/trie.hh"

#include "lm/bhiksha.hh"
#include "lm/quantize.hh"
#include "util/bit_packing.hh"
#include "util/exception.hh"
#include "util/sorted_uniform.hh"

#include <assert.h>

namespace lm {
namespace ngram {
namespace trie {
namespace {

class KeyAccessor {
  public:
    KeyAccessor(const void *base, uint64_t key_mask, uint8_t key_bits, uint8_t total_bits) 
      : base_(reinterpret_cast<const uint8_t*>(base)), key_mask_(key_mask), key_bits_(key_bits), total_bits_(total_bits) {}

    typedef uint64_t Key;

    Key operator()(uint64_t index) const {
      return util::ReadInt57(base_, index * static_cast<uint64_t>(total_bits_), key_bits_, key_mask_);
    }

  private:
    const uint8_t *const base_;
    const WordIndex key_mask_;
    const uint8_t key_bits_, total_bits_;
};

bool FindBitPacked(const void *base, uint64_t key_mask, uint8_t key_bits, uint8_t total_bits, uint64_t begin_index, uint64_t end_index, const uint64_t max_vocab, const uint64_t key, uint64_t &at_index) {
  KeyAccessor accessor(base, key_mask, key_bits, total_bits);
  if (!util::BoundedSortedUniformFind<uint64_t, KeyAccessor, util::PivotSelect<sizeof(WordIndex)>::T>(accessor, begin_index - 1, (uint64_t)0, end_index, max_vocab, key, at_index)) return false;
  return true;
}
} // namespace

std::size_t BitPacked::BaseSize(uint64_t entries, uint64_t max_vocab, uint8_t remaining_bits) {
  uint8_t total_bits = util::RequiredBits(max_vocab) + remaining_bits;
  // Extra entry for next pointer at the end.  
  // +7 then / 8 to round up bits and convert to bytes
  // +sizeof(uint64_t) so that ReadInt57 etc don't go segfault.  
  // Note that this waste is O(order), not O(number of ngrams).
  return ((1 + entries) * total_bits + 7) / 8 + sizeof(uint64_t);
}

void BitPacked::BaseInit(void *base, uint64_t max_vocab, uint8_t remaining_bits) {
  util::BitPackingSanity();
  word_bits_ = util::RequiredBits(max_vocab);
  word_mask_ = (1ULL << word_bits_) - 1ULL;
  if (word_bits_ > 57) UTIL_THROW(util::Exception, "Sorry, word indices more than " << (1ULL << 57) << " are not implemented.  Edit util/bit_packing.hh and fix the bit packing functions.");
  total_bits_ = word_bits_ + remaining_bits;

  base_ = static_cast<uint8_t*>(base);
  insert_index_ = 0;
  max_vocab_ = max_vocab;
}

template <class Quant, class Bhiksha> std::size_t BitPackedMiddle<Quant, Bhiksha>::Size(uint8_t quant_bits, uint64_t entries, uint64_t max_vocab, uint64_t max_ptr, const Config &config) {
  return Bhiksha::Size(entries + 1, max_ptr, config) + BaseSize(entries, max_vocab, quant_bits + Bhiksha::InlineBits(entries + 1, max_ptr, config));
}

template <class Quant, class Bhiksha> BitPackedMiddle<Quant, Bhiksha>::BitPackedMiddle(void *base, const Quant &quant, uint64_t entries, uint64_t max_vocab, uint64_t max_next, const BitPacked &next_source, const Config &config) :
  BitPacked(),
  quant_(quant),
  // If the offset of the method changes, also change TrieSearch::UpdateConfigFromBinary.
  bhiksha_(base, entries + 1, max_next, config),
  next_source_(&next_source) {
  if (entries + 1 >= (1ULL << 57) || (max_next >= (1ULL << 57)))  UTIL_THROW(util::Exception, "Sorry, this does not support more than " << (1ULL << 57) << " n-grams of a particular order.  Edit util/bit_packing.hh and fix the bit packing functions.");
  BaseInit(reinterpret_cast<uint8_t*>(base) + Bhiksha::Size(entries + 1, max_next, config), max_vocab, quant.TotalBits() + bhiksha_.InlineBits());
}

template <class Quant, class Bhiksha> void BitPackedMiddle<Quant, Bhiksha>::Insert(WordIndex word, float prob, float backoff) {
  assert(word <= word_mask_);
  uint64_t at_pointer = insert_index_ * total_bits_;

  util::WriteInt57(base_, at_pointer, word_bits_, word);
  at_pointer += word_bits_;
  quant_.Write(base_, at_pointer, prob, backoff);
  at_pointer += quant_.TotalBits();
  uint64_t next = next_source_->InsertIndex();
  bhiksha_.WriteNext(base_, at_pointer, insert_index_, next);

  ++insert_index_;
}

template <class Quant, class Bhiksha> bool BitPackedMiddle<Quant, Bhiksha>::Find(WordIndex word, float &prob, float &backoff, NodeRange &range, uint64_t &pointer) const {
  uint64_t at_pointer;
  if (!FindBitPacked(base_, word_mask_, word_bits_, total_bits_, range.begin, range.end, max_vocab_, word, at_pointer)) {
    return false;
  }
  pointer = at_pointer;
  at_pointer *= total_bits_;
  at_pointer += word_bits_;

  quant_.Read(base_, at_pointer, prob, backoff);
  at_pointer += quant_.TotalBits();

  bhiksha_.ReadNext(base_, at_pointer, pointer, total_bits_, range);

  return true;
}

template <class Quant, class Bhiksha> bool BitPackedMiddle<Quant, Bhiksha>::FindNoProb(WordIndex word, float &backoff, NodeRange &range) const {
  uint64_t index;
  if (!FindBitPacked(base_, word_mask_, word_bits_, total_bits_, range.begin, range.end, max_vocab_, word, index)) return false;
  uint64_t at_pointer = index * total_bits_;
  at_pointer += word_bits_;
  quant_.ReadBackoff(base_, at_pointer, backoff);
  at_pointer += quant_.TotalBits();
  bhiksha_.ReadNext(base_, at_pointer, index, total_bits_, range);
  return true;
}

template <class Quant, class Bhiksha> void BitPackedMiddle<Quant, Bhiksha>::FinishedLoading(uint64_t next_end, const Config &config) {
  uint64_t last_next_write = (insert_index_ + 1) * total_bits_ - bhiksha_.InlineBits();
  bhiksha_.WriteNext(base_, last_next_write, insert_index_ + 1, next_end);
  bhiksha_.FinishedLoading(config);
}

template <class Quant> void BitPackedLongest<Quant>::Insert(WordIndex index, float prob) {
  assert(index <= word_mask_);
  uint64_t at_pointer = insert_index_ * total_bits_;
  util::WriteInt57(base_, at_pointer, word_bits_, index);
  at_pointer += word_bits_;
  quant_.Write(base_, at_pointer, prob);
  ++insert_index_;
}

template <class Quant> bool BitPackedLongest<Quant>::Find(WordIndex word, float &prob, const NodeRange &range) const {
  uint64_t at_pointer;
  if (!FindBitPacked(base_, word_mask_, word_bits_, total_bits_, range.begin, range.end, max_vocab_, word, at_pointer)) return false;
  at_pointer = at_pointer * total_bits_ + word_bits_;
  quant_.Read(base_, at_pointer, prob);
  return true;
}

template class BitPackedMiddle<DontQuantize::Middle, DontBhiksha>;
template class BitPackedMiddle<DontQuantize::Middle, ArrayBhiksha>;
template class BitPackedMiddle<SeparatelyQuantize::Middle, DontBhiksha>;
template class BitPackedMiddle<SeparatelyQuantize::Middle, ArrayBhiksha>;
template class BitPackedLongest<DontQuantize::Longest>;
template class BitPackedLongest<SeparatelyQuantize::Longest>;

} // namespace trie
} // namespace ngram
} // namespace lm