Add fp32 distance computation option in NN Descent

c/include/cuvs/neighbors/nn_descent.h

@@ -34,6 +34,10 @@ extern "C" {
  * `max_iterations`: The number of iterations that nn-descent will refine
  * the graph for. More iterations produce a better quality graph at cost of performance
  * `termination_threshold`: The delta at which nn-descent will terminate its iterations
+ * `return_distances`: Boolean to decide whether to return distances array
+ * `fp32_dist_computation`: Boolean to decide whether to use fp32 distance computation for better
+ * precision at the cost of performance and memory usage. We recommend using this for smaller
+ * dimensions or if the distances array is needed for precision-sensitive workloads.
  */
 struct cuvsNNDescentIndexParams {
   cuvsDistanceType metric;
@@ -43,6 +47,7 @@ struct cuvsNNDescentIndexParams {
   size_t max_iterations;
   float termination_threshold;
   bool return_distances;
+  bool fp32_dist_computation;
 };
 
 typedef struct cuvsNNDescentIndexParams* cuvsNNDescentIndexParams_t;

c/src/neighbors/nn_descent.cpp

@@ -43,6 +43,7 @@ void* _build(cuvsResources_t res,
   build_params.max_iterations            = params.max_iterations;
   build_params.termination_threshold     = params.termination_threshold;
   build_params.return_distances          = params.return_distances;
+  build_params.fp32_dist_computation      = params.fp32_dist_computation;
 
   using graph_type = raft::host_matrix_view<IdxT, int64_t, raft::row_major>;
   std::optional<graph_type> graph;
@@ -177,7 +178,8 @@ extern "C" cuvsError_t cuvsNNDescentIndexParamsCreate(cuvsNNDescentIndexParams_t
       .intermediate_graph_degree = cpp_params.intermediate_graph_degree,
       .max_iterations            = cpp_params.max_iterations,
       .termination_threshold     = cpp_params.termination_threshold,
-      .return_distances          = cpp_params.return_distances};
+      .return_distances          = cpp_params.return_distances,
+    .fp32_dist_computation      = cpp_params.fp32_dist_computation};
   });
 }
 

cpp/include/cuvs/neighbors/nn_descent.hpp

@@ -37,13 +37,17 @@ namespace cuvs::neighbors::nn_descent {
  * the graph for. More iterations produce a better quality graph at cost of performance
  * - `termination_threshold`: The delta at which nn-descent will terminate its iterations
  * - `return_distances`: Boolean to decide whether to return distances array
+ * - `fp32_dist_computation`: Boolean to decide whether to use fp32 distance computation for better
+ * precision at the cost of performance and memory usage. We recommend using this for smaller
+ * dimensions or if the distances array is needed for precision-sensitive workloads.
  */
 struct index_params : cuvs::neighbors::index_params {
   size_t graph_degree              = 64;
   size_t intermediate_graph_degree = 128;
   size_t max_iterations            = 20;
   float termination_threshold      = 0.0001;
   bool return_distances            = true;
+  bool fp32_dist_computation       = false;
 
   /** @brief Construct NN descent parameters for a specific kNN graph degree
    *