SERVER-23990 add ValueComparator::Hasher for collation-aware Value hashing

3 files changed, 19 insertions, 9 deletions

diff --git a/src/mongo/base/simple_string_data_comparator.cpp b/src/mongo/base/simple_string_data_comparator.cpp
index e52539744fc..f9077f942b2 100644
--- a/src/mongo/base/simple_string_data_comparator.cpp
+++ b/src/mongo/base/simple_string_data_comparator.cpp
@@ -40,19 +40,19 @@ namespace mongo {
 namespace {
 
 template <int SizeofSizeT>
-size_t murmur3(StringData str);
+size_t murmur3(StringData str, size_t seed);
 
 template <>
-size_t murmur3<4>(StringData str) {
+size_t murmur3<4>(StringData str, size_t seed) {
     char hash[4];
-    MurmurHash3_x86_32(str.rawData(), str.size(), 0, &hash);
+    MurmurHash3_x86_32(str.rawData(), str.size(), seed, &hash);
     return ConstDataView(hash).read<LittleEndian<std::uint32_t>>();
 }
 
 template <>
-size_t murmur3<8>(StringData str) {
+size_t murmur3<8>(StringData str, size_t seed) {
     char hash[16];
-    MurmurHash3_x64_128(str.rawData(), str.size(), 0, hash);
+    MurmurHash3_x64_128(str.rawData(), str.size(), seed, hash);
     return static_cast<size_t>(ConstDataView(hash).read<LittleEndian<std::uint64_t>>());
 }
 
@@ -64,8 +64,8 @@ int SimpleStringDataComparator::compare(StringData left, StringData right) const
     return left.compare(right);
 }
 
-size_t SimpleStringDataComparator::hash(StringData stringToHash) const {
-    return murmur3<sizeof(size_t)>(stringToHash);
+void SimpleStringDataComparator::hash_combine(size_t& seed, StringData stringToHash) const {
+    seed = murmur3<sizeof(size_t)>(stringToHash, seed);
 }
 
 }  // namespace mongo
diff --git a/src/mongo/base/simple_string_data_comparator.h b/src/mongo/base/simple_string_data_comparator.h
index c494a034726..77a8d0e1ef7 100644
--- a/src/mongo/base/simple_string_data_comparator.h
+++ b/src/mongo/base/simple_string_data_comparator.h
@@ -45,7 +45,7 @@ public:
 
     int compare(StringData left, StringData right) const override;
 
-    size_t hash(StringData stringToHash) const override;
+    void hash_combine(size_t& seed, StringData stringToHash) const override;
 };
 
 }  // namespace mongo
diff --git a/src/mongo/base/string_data_comparator_interface.h b/src/mongo/base/string_data_comparator_interface.h
index ac4654a479a..c5e730bc1c0 100644
--- a/src/mongo/base/string_data_comparator_interface.h
+++ b/src/mongo/base/string_data_comparator_interface.h
@@ -94,7 +94,17 @@ public:
     /**
      * Hash a StringData in a way that respects this comparator.
      */
-    virtual size_t hash(StringData stringToHash) const = 0;
+    size_t hash(StringData stringToHash) const {
+        size_t seed = 0;
+        hash_combine(seed, stringToHash);
+        return seed;
+    }
+
+    /**
+     * Hash a StringData in a way that respects this comparator, and return the result in the 'seed'
+     * in-out parameter.
+     */
+    virtual void hash_combine(size_t& seed, StringData stringToHash) const = 0;
 
     /**
      * Returns a function object which can evaluate string equality according to this comparator.