Fix OPQ dimension parsing (#2147)

Summary:
Pull Request resolved: #2147

There was a bug in the OPQ string parsing. This diff adds a test and fixes the error.

Reviewed By: aijanai

Differential Revision: D33020167

fbshipit-source-id: 32e43653849b258a3b6d0cfdc44a6c637433f2c8

Author: mdouze

faiss/index_factory.cpp

@@ -203,7 +203,7 @@ VectorTransform* parse_VectorTransform(const std::string& description, int d) {
     }
     if (match("OPQ([0-9]+)(_[0-9]+)?")) {
         int M = std::stoi(sm[1].str());
-        int d_out = mres_to_int(sm[2], d);
+        int d_out = mres_to_int(sm[2], d, 1);
         return new OPQMatrix(d, M, d_out);
     }
     if (match("Pad([0-9]+)")) {

tests/test_factory.py

@@ -39,6 +39,7 @@ def test_factory_2(self):
         index = faiss.index_factory(12, "SQ8")
         assert index.code_size == 12
 
+
     def test_factory_3(self):
 
         index = faiss.index_factory(12, "IVF10,PQ4")
@@ -53,6 +54,13 @@ def test_factory_4(self):
         index = faiss.index_factory(12, "IVF10,FlatDedup")
         assert index.instances is not None
 
+    def test_factory_5(self):
+        index = faiss.index_factory(128, "OPQ16,Flat")
+        assert index.sa_code_size() == 128 * 4
+        index = faiss.index_factory(128, "OPQ16_64,Flat")
+        assert index.sa_code_size() == 64 * 4
+        assert index.chain.at(0).d_out == 64
+
     def test_factory_HNSW(self):
         index = faiss.index_factory(12, "HNSW32")
         assert index.storage.sa_code_size() == 12 * 4
@@ -61,7 +69,6 @@ def test_factory_HNSW(self):
         index = faiss.index_factory(12, "HNSW32_PQ4")
         assert index.storage.sa_code_size() == 4
 
-
     def test_factory_HNSW_newstyle(self):
         index = faiss.index_factory(12, "HNSW32,Flat")
         assert index.storage.sa_code_size() == 12 * 4