The interface addPoint is changed from

addPoint(void*, args...) to addPoint(const void*, args...).

The changes include the interface in bruteforce.h, and all interfaces
related to addPoint in hnswlib.

I test the code using 1 million sift data, the result is ok.

Author: orrorcol

hnswlib/bruteforce.h

@@ -40,7 +40,7 @@ namespace hnswlib {
 
         std::unordered_map<labeltype,size_t > dict_external_to_internal;
 
-        void addPoint(void *datapoint, labeltype label) {
+        void addPoint(const void *datapoint, labeltype label) {
 
             int idx;
             {

hnswlib/hnswalg.h

@@ -150,7 +150,7 @@ namespace hnswlib {
         }
 
         std::priority_queue<std::pair<dist_t, tableint>, std::vector<std::pair<dist_t, tableint>>, CompareByFirst>
-        searchBaseLayer(tableint ep_id, void *data_point, int layer) {
+        searchBaseLayer(tableint ep_id, const void *data_point, int layer) {
             VisitedList *vl = visited_list_pool_->getFreeVisitedList();
             vl_type *visited_array = vl->mass;
             vl_type visited_array_tag = vl->curV;
@@ -371,7 +371,7 @@ namespace hnswlib {
             return (linklistsizeint *) (linkLists_[internal_id] + (level - 1) * size_links_per_element_);
         };
 
-        void mutuallyConnectNewElement(void *data_point, tableint cur_c,
+        void mutuallyConnectNewElement(const void *data_point, tableint cur_c,
                                        std::priority_queue<std::pair<dist_t, tableint>, std::vector<std::pair<dist_t, tableint>>, CompareByFirst> top_candidates,
                                        int level) {
 
@@ -779,11 +779,11 @@ namespace hnswlib {
             *((unsigned short int*)(ptr))=*((unsigned short int *)&size);
         }
 
-        void addPoint(void *data_point, labeltype label) {
+        void addPoint(const void *data_point, labeltype label) {
             addPoint(data_point, label,-1);
         }
 
-        tableint addPoint(void *data_point, labeltype label, int level) {
+        tableint addPoint(const void *data_point, labeltype label, int level) {
             tableint cur_c = 0;
             {
                 std::unique_lock <std::mutex> lock(cur_element_count_guard_);

hnswlib/hnswlib.h

@@ -60,7 +60,7 @@ namespace hnswlib {
     template<typename dist_t>
     class AlgorithmInterface {
     public:
-        virtual void addPoint(void *datapoint, labeltype label)=0;
+        virtual void addPoint(const void *datapoint, labeltype label)=0;
         virtual std::priority_queue<std::pair<dist_t, labeltype >> searchKnn(const void *, size_t) const = 0;
         virtual void saveIndex(const std::string &location)=0;
         virtual ~AlgorithmInterface(){