From 7c38f6b98774a917cc4c13cea9f02b3a18155ff5 Mon Sep 17 00:00:00 2001
From: lry22221111 <2247557140@qq.com>
Date: Fri, 17 Jan 2025 15:10:29 +0800
Subject: [PATCH] [feat]Add calculate hamming distance

---
 faiss/MetricType.h                |  1 +
 faiss/utils/extra_distances-inl.h | 14 ++++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/faiss/MetricType.h b/faiss/MetricType.h
index 8e889b1a03..7506a29713 100644
--- a/faiss/MetricType.h
+++ b/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
diff --git a/faiss/utils/extra_distances-inl.h b/faiss/utils/extra_distances-inl.h
index cf89c47629..fc267c44b5 100644
--- a/faiss/utils/extra_distances-inl.h
+++ b/faiss/utils/extra_distances-inl.h
@@ -13,6 +13,8 @@
 #include <faiss/utils/distances.h>
 #include <cmath>
 #include <type_traits>
+#include <cstddef> 
+#include <faiss/utils/hamming_distance/common.h>
 
 namespace faiss {
 
@@ -23,6 +25,7 @@ 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<
@@ -45,6 +48,17 @@ 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,