Merge pull request #4 from LiuRuoyu01/main

[feat]Add calculate hamming distance

Author: yuhaijun999

faiss/MetricType.h

@@ -25,6 +25,7 @@ enum MetricType {
     METRIC_L1,                ///< L1 (aka cityblock)
     METRIC_Linf,              ///< infinity distance
     METRIC_Lp,                ///< L_p distance, p is given by a faiss::Index
+    METRIC_HAMMING,           ///< Hamming distance for binary vectors  
                               /// metric_arg
 
     /// some additional metrics defined in scipy.spatial.distance

faiss/utils/extra_distances-inl.h

@@ -10,7 +10,10 @@
 
 #include <faiss/MetricType.h>
 #include <faiss/utils/distances.h>
+#include <climits>
 #include <type_traits>
+#include <cstddef> 
+#include <faiss/utils/hamming_distance/common.h>
 
 namespace faiss {
 
@@ -21,6 +24,7 @@ struct VectorDistance {
     static constexpr bool is_similarity = is_similarity_metric(mt);
 
     inline float operator()(const float* x, const float* y) const;
+    inline size_t operator()(const uint8_t* x, const uint8_t* y) const;
 
     // heap template to use for this type of metric
     using C = typename std::conditional<
@@ -43,6 +47,17 @@ inline float VectorDistance<METRIC_INNER_PRODUCT>::operator()(
     return fvec_inner_product(x, y, d);
 }
 
+template<>
+inline size_t VectorDistance<METRIC_HAMMING>::operator()(
+        const uint8_t* x,
+        const uint8_t* y) const {
+    int h = 0;
+    for (size_t i = 0; i < d; i++) {
+        h += (int)hamdis_tab_ham_bytes[x[i] ^ y[i]];
+    }
+    return h;
+}
+
 template <>
 inline float VectorDistance<METRIC_L1>::operator()(
         const float* x,