Add cpp tutorial for index factory refine index construction (facebookresearch#3494)

Summary:

This tasks focus on the refine index construction tutorial with different index refinement on fp16/sq8 quantization. The python version was added a while ago.

Differential Revision: D58161983

Author: Xiao Fu

tutorial/cpp/9-RefineComparison.cpp

@@ -0,0 +1,107 @@
+/**
+ * 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.
+ */
+
+#include <cassert>
+#include <cstdio>
+#include <cstdlib>
+#include <random>
+
+#include <faiss/IndexPQFastScan.h>
+#include <faiss/IndexRefine.h>
+#include <faiss/index_factory.h>
+using idx_t = faiss::idx_t;
+
+int main() {
+    int d = 64;      // dimension
+    int nb = 100000; // database size
+    int nq = 10000;  // nb of queries
+
+    std::mt19937 rng;
+    std::uniform_real_distribution<> distrib;
+
+    float* xb = new float[(int)(d * nb)];
+    float* xq = new float[(int)(d * nq)];
+
+    for (int i = 0; i < nb; i++) {
+        for (int j = 0; j < d; j++) {
+            xb[d * i + j] = distrib(rng);
+        }
+        xb[d * i] += i / 1000.;
+    }
+
+    for (int i = 0; i < nq; i++) {
+        for (int j = 0; j < d; j++) {
+            xq[d * i + j] = distrib(rng);
+        }
+        xq[d * i] += i / 1000.;
+    }
+
+    int m = 8;
+    int n_bit = 4;
+
+    // Constructing the refine PQ index with SQfp16 with index factory
+    faiss::Index* index_fp16;
+    index_fp16 = faiss::index_factory(
+            d, "PQ32x4fs,Refine(SQfp16)", faiss::METRIC_L2);
+    index_fp16->train(nb, xb);
+    index_fp16->add(nb, xb);
+
+    // Constructing the refine PQ index with SQ8
+    faiss::Index* index_sq8;
+    index_sq8 =
+            faiss::index_factory(d, "PQ32x4fs,Refine(SQ8)", faiss::METRIC_L2);
+    index_sq8->train(nb, xb);
+    index_sq8->add(nb, xb);
+
+    int k = 10;
+    { // search xq
+        idx_t* I_fp16 = new idx_t[(int)(k * nq)];
+        float* D_fp16 = new float[(int)(k * nq)];
+        idx_t* I_sq8 = new idx_t[(int)(k * nq)];
+        float* D_sq8 = new float[(int)(k * nq)];
+
+        // Parameterization on k factor while doing search for index refinement
+        float k_factor = 3;
+        faiss::IndexRefineSearchParameters* params =
+                new faiss::IndexRefineSearchParameters();
+        params->k_factor = k_factor;
+
+        // Perform index search using different index refinement
+        index_fp16->search(nq, xq, k, D_fp16, I_fp16, params);
+        index_sq8->search(nq, xq, k, D_sq8, I_sq8, params);
+
+        printf("I_fp16=\n");
+        for (int i = nq - 5; i < nq; i++) {
+            for (int j = 0; j < k; j++) {
+                printf("%5zd ", I_fp16[i * k + j]);
+            }
+            printf("\n");
+        }
+
+        printf("I_sq8=\n");
+        for (int i = nq - 5; i < nq; i++) {
+            for (int j = 0; j < k; j++) {
+                printf("%5zd ", I_sq8[i * k + j]);
+            }
+            printf("\n");
+        }
+
+        delete[] I_fp16;
+        delete[] D_fp16;
+        delete[] I_sq8;
+        delete[] D_sq8;
+        delete params;
+
+        delete index_fp16;
+        delete index_sq8;
+    }
+
+    delete[] xb;
+    delete[] xq;
+
+    return 0;
+}

tutorial/cpp/CMakeLists.txt

@@ -27,3 +27,6 @@ target_link_libraries(7-PQFastScan PRIVATE faiss)
 
 add_executable(8-PQFastScanRefine EXCLUDE_FROM_ALL 8-PQFastScanRefine.cpp)
 target_link_libraries(8-PQFastScanRefine PRIVATE faiss)
+
+add_executable(9-RefineComparison EXCLUDE_FROM_ALL 9-RefineComparison.cpp)
+target_link_libraries(9-RefineComparison PRIVATE faiss)