Move static functions to header file (facebookresearch#3757)

Summary:
Pull Request resolved: facebookresearch#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

@@ -5,6 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#include <faiss/impl/index_read_utils.h>
 #include <faiss/index_io.h>
 
 #include <faiss/impl/io_macros.h>
@@ -61,7 +62,7 @@ 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 +231,7 @@ 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 +439,7 @@ 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 +455,10 @@ 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/impl/index_read_utils.h

@@ -0,0 +1,30 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// Utils for index_read
+
+#ifndef FAISS_INDEX_READ_UTILS_H
+#define FAISS_INDEX_READ_UTILS_H
+
+#include <faiss/IndexIVF.h>
+#include <faiss/impl/io.h>
+
+#pragma once
+
+namespace faiss {
+
+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