Move static functions to header file (#3757)

Summary:
Pull Request resolved: #3757

In the telemetry wrapper, we need to wrap read_index to return wrapped index structs. D61049751

This read_index wrapper calls several static functions. These are not callable outside a C++ file. Thus this diff changes them to non static and declares them in the header file. Then the wrapper is able to call them.

Differential Revision: D61282004

Author: Michael Norris

faiss/impl/index_read.cpp

@@ -61,7 +61,7 @@ namespace faiss {
  * Read
  **************************************************************/
 
-static void read_index_header(Index* idx, IOReader* f) {
+void read_index_header(Index* idx, IOReader* f) {
     READ1(idx->d);
     READ1(idx->ntotal);
     idx_t dummy;
@@ -230,7 +230,7 @@ InvertedLists* read_InvertedLists(IOReader* f, int io_flags) {
     }
 }
 
-static void read_InvertedLists(IndexIVF* ivf, IOReader* f, int io_flags) {
+void read_InvertedLists(IndexIVF* ivf, IOReader* f, int io_flags) {
     InvertedLists* ils = read_InvertedLists(f, io_flags);
     if (ils) {
         FAISS_THROW_IF_NOT(ils->nlist == ivf->nlist);
@@ -438,7 +438,7 @@ ProductQuantizer* read_ProductQuantizer(IOReader* reader) {
     return pq;
 }
 
-static void read_direct_map(DirectMap* dm, IOReader* f) {
+void read_direct_map(DirectMap* dm, IOReader* f) {
     char maintain_direct_map;
     READ1(maintain_direct_map);
     dm->type = (DirectMap::Type)maintain_direct_map;
@@ -454,10 +454,10 @@ static void read_direct_map(DirectMap* dm, IOReader* f) {
     }
 }
 
-static void read_ivf_header(
+void read_ivf_header(
         IndexIVF* ivf,
         IOReader* f,
-        std::vector<std::vector<idx_t>>* ids = nullptr) {
+        std::vector<std::vector<idx_t>>* ids) {
     read_index_header(ivf, f);
     READ1(ivf->nlist);
     READ1(ivf->nprobe);

faiss/index_io.h

@@ -10,6 +10,7 @@
 #ifndef FAISS_INDEX_IO_H
 #define FAISS_INDEX_IO_H
 
+#include <faiss/IndexIVF.h>
 #include <cstdio>
 #include <string>
 #include <typeinfo>
@@ -86,6 +87,14 @@ void write_ProductQuantizer(const ProductQuantizer* pq, IOWriter* f);
 void write_InvertedLists(const InvertedLists* ils, IOWriter* f);
 InvertedLists* read_InvertedLists(IOReader* reader, int io_flags = 0);
 
+void read_index_header(Index* idx, IOReader* f);
+void read_direct_map(DirectMap* dm, IOReader* f);
+void read_ivf_header(
+        IndexIVF* ivf,
+        IOReader* f,
+        std::vector<std::vector<idx_t>>* ids = nullptr);
+void read_InvertedLists(IndexIVF* ivf, IOReader* f, int io_flags);
+
 } // namespace faiss
 
 #endif