X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=folly%2FHash.h;h=109b24e40e5478b1a2954c6b108376a02d76c9b5;hb=46e3ed2921bd4e5de81fbc36fcb6a82d30d1499f;hp=1cbeda6a81e5723786760c0d77a52b208d0b8ca1;hpb=148cba11ab1b0d20f17485bd80fcc7e7214f5cca;p=folly.git

diff --git a/folly/Hash.h b/folly/Hash.h
index 1cbeda6a..109b24e4 100644
--- a/folly/Hash.h
+++ b/folly/Hash.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012 Facebook, Inc.
+ * Copyright 2014 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,9 +21,10 @@
 #include <stdint.h>
 #include <string>
 #include <utility>
+#include <tuple>
 
-#include "folly/SpookyHashV1.h"
-#include "folly/SpookyHashV2.h"
+#include <folly/SpookyHashV1.h>
+#include <folly/SpookyHashV2.h>
 
 /*
  * Various hashing functions.
@@ -32,14 +33,11 @@
 namespace folly { namespace hash {
 
 // This is a general-purpose way to create a single hash from multiple
-// hashable objects. It relies on std::hash<T> being available for all
-// relevant types and combines those hashes in an order-dependent way
-// to yield a new hash.
+// hashable objects. hash_combine_generic takes a class Hasher implementing
+// hash<T>; hash_combine uses a default hasher StdHasher that uses std::hash.
+// hash_combine_generic hashes each argument and combines those hashes in
+// an order-dependent way to yield a new hash.
 
-// Never used, but gcc demands it.
-inline size_t hash_combine() {
-  return 0;
-}
 
 // This is the Hash128to64 function from Google's cityhash (available
 // under the MIT License).  We use it to reduce multiple 64 bit hashes
@@ -55,16 +53,52 @@ inline size_t hash_128_to_64(const size_t upper, const size_t lower) {
   return b;
 }
 
-template <typename T, typename... Ts>
-size_t hash_combine(const T& t, const Ts&... ts) {
-  size_t seed = std::hash<T>()(t);
+// Never used, but gcc demands it.
+template <class Hasher>
+inline size_t hash_combine_generic() {
+  return 0;
+}
+
+template <
+    class Iter,
+    class Hash = std::hash<typename std::iterator_traits<Iter>::value_type>>
+uint64_t hash_range(Iter begin,
+                    Iter end,
+                    uint64_t hash = 0,
+                    Hash hasher = Hash()) {
+  for (; begin != end; ++begin) {
+    hash = hash_128_to_64(hash, hasher(*begin));
+  }
+  return hash;
+}
+
+template <class Hasher, typename T, typename... Ts>
+size_t hash_combine_generic(const T& t, const Ts&... ts) {
+  size_t seed = Hasher::hash(t);
   if (sizeof...(ts) == 0) {
     return seed;
   }
-  size_t remainder = hash_combine(ts...);
+  size_t remainder = hash_combine_generic<Hasher>(ts...);
   return hash_128_to_64(seed, remainder);
 }
 
+// Simply uses std::hash to hash.  Note that std::hash is not guaranteed
+// to be a very good hash function; provided std::hash doesn't collide on
+// the individual inputs, you are fine, but that won't be true for, say,
+// strings or pairs
+class StdHasher {
+ public:
+  template <typename T>
+  static size_t hash(const T& t) {
+    return std::hash<T>()(t);
+  }
+};
+
+template <typename T, typename... Ts>
+size_t hash_combine(const T& t, const Ts&... ts) {
+  return hash_combine_generic<StdHasher>(t, ts...);
+}
+
 //////////////////////////////////////////////////////////////////////
 
 /*
@@ -169,7 +203,7 @@ inline uint32_t jenkins_rev_unmix32(uint32_t key) {
  *     http://www.isthe.com/chongo/tech/comp/fnv/
  */
 
-const uint32_t FNV_32_HASH_START = 216613626UL;
+const uint32_t FNV_32_HASH_START = 2166136261UL;
 const uint64_t FNV_64_HASH_START = 14695981039346656037ULL;
 
 inline uint32_t fnv32(const char* s,
@@ -197,7 +231,7 @@ inline uint32_t fnv32_buf(const void* buf,
 }
 
 inline uint32_t fnv32(const std::string& str,
-                      uint64_t hash = FNV_32_HASH_START) {
+                      uint32_t hash = FNV_32_HASH_START) {
   return fnv32_buf(str.data(), str.size(), hash);
 }
 
@@ -328,6 +362,26 @@ template<> struct hasher<uint64_t> {
   }
 };
 
+// recursion
+template <size_t index, typename... Ts>
+struct TupleHasher {
+  size_t operator()(std::tuple<Ts...> const& key) const {
+    return hash::hash_combine(
+      TupleHasher<index - 1, Ts...>()(key),
+      std::get<index>(key));
+  }
+};
+
+// base
+template <typename... Ts>
+struct TupleHasher<0, Ts...> {
+  size_t operator()(std::tuple<Ts...> const& key) const {
+    // we could do std::hash here directly, but hash_combine hides all the
+    // ugly templating implicitly
+    return hash::hash_combine(std::get<0>(key));
+  }
+};
+
 } // namespace folly
 
 // Custom hash functions.
@@ -341,6 +395,18 @@ namespace std {
       return folly::hash::hash_combine(x.first, x.second);
     }
   };
+
+  // Hash function for tuples. Requires default hash functions for all types.
+  template <typename... Ts>
+  struct hash<std::tuple<Ts...>> {
+    size_t operator()(std::tuple<Ts...> const& key) const {
+      folly::TupleHasher<
+        std::tuple_size<std::tuple<Ts...>>::value - 1, // start index
+        Ts...> hasher;
+
+      return hasher(key);
+    }
+  };
 } // namespace std
 
 #endif