Now check during reduce phase whether there are no neighbors. For 64-…

…bit build.

src/Makevars

@@ -1,5 +1,5 @@
 PKG_CFLAGS = $(SHLIB_OPENMP_CFLAGS)
 PKG_LIBS = $(SHLIB_OPENMP_CXXFLAGS) $(SHLIB_OPENMP_CFLAGS) $(FLIBS) $(LAPACK_LIBS) $(BLAS_LIBS)
-PKG_CXXFLAGS = $(SHLIB_OPENMP_CXXFLAGS)
+PKG_CXXFLAGS = $(SHLIB_OPENMP_CXXFLAGS) -DARMA_64BIT_WORD
 CXX_STD=CXX11
 LDFLAGS = $(LDFLAGS)

src/distance.cpp

@@ -63,7 +63,7 @@ arma::vec fastDistance(const IntegerVector is,
 #ifdef _OPENMP
 #pragma omp parallel for shared (xs)
 #endif
-  for (vertexidxtype i=0; i < is.length(); i++) if (p.increment()) xs[i] =
+  for (arma::uword i=0; i < is.length(); i++) if (p.increment()) xs[i] =
     distanceFunction(data.col(is[i]), data.col(js[i]));
   return xs;
 };

src/neighbors.cpp

@@ -165,6 +165,7 @@ void AnnoySearch<M, V>::reduceOne(const vertexidxtype& i,
 	 */
 	auto continueWriting = std::transform(newNeighborhood.begin(), newNeighborhood.end(), knns.begin_col(i),
                                         [](const std::pair<distancetype, vertexidxtype>& input) {return input.second;});
+	if (continueWriting == knns.begin_col(i)) stop("At reduction, no neighbors for vertex " + std::to_string(i));
 	sort(knns.begin_col(i), continueWriting);
 	std::fill(continueWriting, knns.end_col(i), -1);
 
@@ -262,14 +263,14 @@ void AnnoySearch<M,V>::exploreOne(const vertexidxtype& i,
 
 	/*
 	* Before the last iteration, we keep the matrix sorted by vertexid, which makes the merge above
-	* more efficient.  In the last iteration, sort by distance.
+	* more efficient.
 	*
 	* We can't use std:copy because we're copying from a vector of pairs
 	*/
 	auto copyContinuation = std::transform(nodeHeap.begin(), nodeHeap.end(), knns.begin_col(i),
                                         [](const std::pair<distancetype, vertexidxtype>& input) {return input.second;});
+	if (copyContinuation == knns.begin_col(i)) stop("No neighbors after exploration - this is a bug. Vertex " + std::to_string(i));
 	sort(knns.begin_col(i), copyContinuation);
-	if (copyContinuation == knns.begin_col(i)) stop("Neighbor exploration failure.");
 	std::fill(copyContinuation, knns.end_col(i), -1);
 }