IndexVectorHasher Struct Reference

#include <nnet-common.h>

Public Member Functions
size_t	operator() (const std::vector< Index > &index_vector) const noexcept

Detailed Description

Definition at line 131 of file nnet-common.h.

Member Function Documentation

operator()()

size_t operator() ( const std::vector< Index > &  index_vector ) const

noexcept

Definition at line 388 of file nnet-common.cc.

                                                         {
  size_t n1 = 15, n2 = 10;  // n1 and n2 are used to extract only a subset of
                            // elements to hash; this makes the hasher faster by
                            // skipping over more elements.  Setting n1 large or
                            // n2 to 1 would make the hasher consider all
                            // elements.
  size_t len = index_vector.size();
  // all long-ish numbers appearing below are randomly chosen primes.
  size_t ans = 1433 + 34949 * len;
  std::vector<Index>::const_iterator iter = index_vector.begin(),
      end = index_vector.end(), med = end;
  if (n1 < len)
    med = iter + n1;

  for (; iter != med; ++iter) {
    ans += iter->n * 1619;
    ans += iter->t * 15649;
    ans += iter->x * 89809;
  }
  // after the first n1 values, look only at every n2'th value.  this makes the
  // hashing much faster, and in the kinds of structures that we actually deal
  // with, we shouldn't get unnecessary hash collisions as a result of this
  // optimization.
  for (; iter < end; iter += n2) {
    ans += iter->n * 1619;
    ans += iter->t * 15649;
    ans += iter->x * 89809;
    // The following if-statement was introduced in order to fix an
    // out-of-range iterator problem on Windows.
    if (n2 > len || iter >= end - n2) 
        break;
  }
  return ans;
}

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The documentation for this struct was generated from the following files:

• nnet3/nnet-common.h
• nnet3/nnet-common.cc