From dce47b8a0cc0e90f93844e66651d68340ed2f940 Mon Sep 17 00:00:00 2001
From: Yedidya Feldblum <yfeldblum@fb.com>
Date: Thu, 19 Oct 2017 02:30:31 -0700
Subject: [PATCH] Revert D6050464: [Folly] Move folly/Hash.h to folly/hash/

Summary:
This reverts commit 64eb65aac8e3e7cd0126e65ca3998bfe167e2d73

bypass-lint

Differential Revision: D6050464

fbshipit-source-id: 1ed63f30837dc11ae57b316f1f7cb233a210894a
---
 folly/AtomicHashArray.h                       |   2 +-
 folly/AtomicHashMap.h                         |   2 +-
 folly/FBString.h                              |   2 +-
 folly/FixedString.h                           |   2 +-
 folly/Hash.h                                  | 502 ++++++++++++++++-
 folly/IPAddressV4.h                           |   2 +-
 folly/IPAddressV6.h                           |   2 +-
 folly/Makefile.am                             |   2 +-
 folly/Singleton.h                             |   2 +-
 folly/SocketAddress.cpp                       |   2 +-
 folly/Uri-inl.h                               |   2 +-
 folly/concurrency/CacheLocality.h             |   2 +-
 .../test/ConcurrentHashMapTest.cpp            |   2 +-
 folly/detail/Futex.cpp                        |   2 +-
 folly/detail/MemoryIdler.h                    |   2 +-
 folly/dynamic.cpp                             |   2 +-
 folly/experimental/FunctionScheduler.h        |   4 +-
 folly/experimental/StringKeyedUnorderedMap.h  |   2 +-
 folly/experimental/StringKeyedUnorderedSet.h  |   2 +-
 folly/experimental/symbolizer/ElfCache.h      |   2 +-
 folly/experimental/test/StringKeyedTest.cpp   |   2 +-
 folly/hash/Hash.h                             | 519 ------------------
 folly/hash/test/ChecksumTest.cpp              |   2 +-
 folly/io/test/CompressionTest.cpp             |   2 +-
 folly/test/AtomicHashArrayTest.cpp            |   2 +-
 folly/test/ConcurrentSkipListBenchmark.cpp    |   2 +-
 folly/{hash => }/test/HashBenchmark.cpp       |   2 +-
 folly/{hash => }/test/HashTest.cpp            |   2 +-
 folly/test/Makefile.am                        |   2 +-
 folly/test/ThreadCachedIntTest.cpp            |   2 +-
 30 files changed, 530 insertions(+), 549 deletions(-)
 delete mode 100644 folly/hash/Hash.h
 rename folly/{hash => }/test/HashBenchmark.cpp (99%)
 rename folly/{hash => }/test/HashTest.cpp (99%)

diff --git a/folly/AtomicHashArray.h b/folly/AtomicHashArray.h
index 654077b1..16b8dad0 100644
--- a/folly/AtomicHashArray.h
+++ b/folly/AtomicHashArray.h
@@ -37,9 +37,9 @@
 #include <boost/iterator/iterator_facade.hpp>
 #include <boost/noncopyable.hpp>
 
+#include <folly/Hash.h>
 #include <folly/ThreadCachedInt.h>
 #include <folly/Utility.h>
-#include <folly/hash/Hash.h>
 
 namespace folly {
 
diff --git a/folly/AtomicHashMap.h b/folly/AtomicHashMap.h
index a3f42c0b..af8aa633 100644
--- a/folly/AtomicHashMap.h
+++ b/folly/AtomicHashMap.h
@@ -92,9 +92,9 @@
 
 #include <folly/AtomicHashArray.h>
 #include <folly/Foreach.h>
+#include <folly/Hash.h>
 #include <folly/Likely.h>
 #include <folly/ThreadCachedInt.h>
-#include <folly/hash/Hash.h>
 
 namespace folly {
 
diff --git a/folly/FBString.h b/folly/FBString.h
index 4cdafcfb..b566d119 100644
--- a/folly/FBString.h
+++ b/folly/FBString.h
@@ -54,9 +54,9 @@
 #include <string>
 #include <utility>
 
+#include <folly/Hash.h>
 #include <folly/Malloc.h>
 #include <folly/Traits.h>
-#include <folly/hash/Hash.h>
 #include <folly/portability/BitsFunctexcept.h>
 
 // When used in folly, assertions are not disabled.
diff --git a/folly/FixedString.h b/folly/FixedString.h
index d94468c1..732ae6ac 100644
--- a/folly/FixedString.h
+++ b/folly/FixedString.h
@@ -409,7 +409,7 @@ struct ReverseIterator {
 } // namespace fixedstring
 } // namespace detail
 
-// Defined in folly/hash/Hash.h
+// Defined in folly/Hash.h
 std::uint32_t hsieh_hash32_buf(const void* buf, std::size_t len);
 
 /** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** *
diff --git a/folly/Hash.h b/folly/Hash.h
index 22b7f14f..410d2720 100644
--- a/folly/Hash.h
+++ b/folly/Hash.h
@@ -16,4 +16,504 @@
 
 #pragma once
 
-#include <folly/hash/Hash.h>
+#include <cstdint>
+#include <cstring>
+#include <limits>
+#include <string>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+
+#include <folly/ApplyTuple.h>
+#include <folly/Bits.h>
+#include <folly/hash/SpookyHashV1.h>
+#include <folly/hash/SpookyHashV2.h>
+
+/*
+ * Various hashing functions.
+ */
+
+namespace folly { namespace hash {
+
+// This is a general-purpose way to create a single hash from multiple
+// 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.
+
+
+// This is the Hash128to64 function from Google's cityhash (available
+// under the MIT License).  We use it to reduce multiple 64 bit hashes
+// into a single hash.
+inline uint64_t hash_128_to_64(const uint64_t upper, const uint64_t lower) {
+  // Murmur-inspired hashing.
+  const uint64_t kMul = 0x9ddfea08eb382d69ULL;
+  uint64_t a = (lower ^ upper) * kMul;
+  a ^= (a >> 47);
+  uint64_t b = (upper ^ a) * kMul;
+  b ^= (b >> 47);
+  b *= kMul;
+  return b;
+}
+
+// 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;
+}
+
+inline uint32_t twang_32from64(uint64_t key);
+
+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_generic<Hasher>(ts...);
+  /* static */ if (sizeof(size_t) == sizeof(uint32_t)) {
+    return twang_32from64((uint64_t(seed) << 32) | remainder);
+  } else {
+    return static_cast<size_t>(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...);
+}
+
+//////////////////////////////////////////////////////////////////////
+
+/*
+ * Thomas Wang 64 bit mix hash function
+ */
+
+inline uint64_t twang_mix64(uint64_t key) {
+  key = (~key) + (key << 21);  // key *= (1 << 21) - 1; key -= 1;
+  key = key ^ (key >> 24);
+  key = key + (key << 3) + (key << 8);  // key *= 1 + (1 << 3) + (1 << 8)
+  key = key ^ (key >> 14);
+  key = key + (key << 2) + (key << 4);  // key *= 1 + (1 << 2) + (1 << 4)
+  key = key ^ (key >> 28);
+  key = key + (key << 31);  // key *= 1 + (1 << 31)
+  return key;
+}
+
+/*
+ * Inverse of twang_mix64
+ *
+ * Note that twang_unmix64 is significantly slower than twang_mix64.
+ */
+
+inline uint64_t twang_unmix64(uint64_t key) {
+  // See the comments in jenkins_rev_unmix32 for an explanation as to how this
+  // was generated
+  key *= 4611686016279904257U;
+  key ^= (key >> 28) ^ (key >> 56);
+  key *= 14933078535860113213U;
+  key ^= (key >> 14) ^ (key >> 28) ^ (key >> 42) ^ (key >> 56);
+  key *= 15244667743933553977U;
+  key ^= (key >> 24) ^ (key >> 48);
+  key = (key + 1) * 9223367638806167551U;
+  return key;
+}
+
+/*
+ * Thomas Wang downscaling hash function
+ */
+
+inline uint32_t twang_32from64(uint64_t key) {
+  key = (~key) + (key << 18);
+  key = key ^ (key >> 31);
+  key = key * 21;
+  key = key ^ (key >> 11);
+  key = key + (key << 6);
+  key = key ^ (key >> 22);
+  return (uint32_t) key;
+}
+
+/*
+ * Robert Jenkins' reversible 32 bit mix hash function
+ */
+
+inline uint32_t jenkins_rev_mix32(uint32_t key) {
+  key += (key << 12);  // key *= (1 + (1 << 12))
+  key ^= (key >> 22);
+  key += (key << 4);   // key *= (1 + (1 << 4))
+  key ^= (key >> 9);
+  key += (key << 10);  // key *= (1 + (1 << 10))
+  key ^= (key >> 2);
+  // key *= (1 + (1 << 7)) * (1 + (1 << 12))
+  key += (key << 7);
+  key += (key << 12);
+  return key;
+}
+
+/*
+ * Inverse of jenkins_rev_mix32
+ *
+ * Note that jenkinks_rev_unmix32 is significantly slower than
+ * jenkins_rev_mix32.
+ */
+
+inline uint32_t jenkins_rev_unmix32(uint32_t key) {
+  // These are the modular multiplicative inverses (in Z_2^32) of the
+  // multiplication factors in jenkins_rev_mix32, in reverse order.  They were
+  // computed using the Extended Euclidean algorithm, see
+  // http://en.wikipedia.org/wiki/Modular_multiplicative_inverse
+  key *= 2364026753U;
+
+  // The inverse of a ^= (a >> n) is
+  // b = a
+  // for (int i = n; i < 32; i += n) {
+  //   b ^= (a >> i);
+  // }
+  key ^=
+    (key >> 2) ^ (key >> 4) ^ (key >> 6) ^ (key >> 8) ^
+    (key >> 10) ^ (key >> 12) ^ (key >> 14) ^ (key >> 16) ^
+    (key >> 18) ^ (key >> 20) ^ (key >> 22) ^ (key >> 24) ^
+    (key >> 26) ^ (key >> 28) ^ (key >> 30);
+  key *= 3222273025U;
+  key ^= (key >> 9) ^ (key >> 18) ^ (key >> 27);
+  key *= 4042322161U;
+  key ^= (key >> 22);
+  key *= 16773121U;
+  return key;
+}
+
+/*
+ * Fowler / Noll / Vo (FNV) Hash
+ *     http://www.isthe.com/chongo/tech/comp/fnv/
+ */
+
+const uint32_t FNV_32_HASH_START = 2166136261UL;
+const uint64_t FNV_64_HASH_START = 14695981039346656037ULL;
+const uint64_t FNVA_64_HASH_START = 14695981039346656037ULL;
+
+inline uint32_t fnv32(const char* buf, uint32_t hash = FNV_32_HASH_START) {
+  // forcing signed char, since other platforms can use unsigned
+  const signed char* s = reinterpret_cast<const signed char*>(buf);
+
+  for (; *s; ++s) {
+    hash += (hash << 1) + (hash << 4) + (hash << 7) +
+            (hash << 8) + (hash << 24);
+    hash ^= *s;
+  }
+  return hash;
+}
+
+inline uint32_t fnv32_buf(const void* buf,
+                          size_t n,
+                          uint32_t hash = FNV_32_HASH_START) {
+  // forcing signed char, since other platforms can use unsigned
+  const signed char* char_buf = reinterpret_cast<const signed char*>(buf);
+
+  for (size_t i = 0; i < n; ++i) {
+    hash += (hash << 1) + (hash << 4) + (hash << 7) +
+            (hash << 8) + (hash << 24);
+    hash ^= char_buf[i];
+  }
+
+  return hash;
+}
+
+inline uint32_t fnv32(const std::string& str,
+                      uint32_t hash = FNV_32_HASH_START) {
+  return fnv32_buf(str.data(), str.size(), hash);
+}
+
+inline uint64_t fnv64(const char* buf, uint64_t hash = FNV_64_HASH_START) {
+  // forcing signed char, since other platforms can use unsigned
+  const signed char* s = reinterpret_cast<const signed char*>(buf);
+
+  for (; *s; ++s) {
+    hash += (hash << 1) + (hash << 4) + (hash << 5) + (hash << 7) +
+      (hash << 8) + (hash << 40);
+    hash ^= *s;
+  }
+  return hash;
+}
+
+inline uint64_t fnv64_buf(const void* buf,
+                          size_t n,
+                          uint64_t hash = FNV_64_HASH_START) {
+  // forcing signed char, since other platforms can use unsigned
+  const signed char* char_buf = reinterpret_cast<const signed char*>(buf);
+
+  for (size_t i = 0; i < n; ++i) {
+    hash += (hash << 1) + (hash << 4) + (hash << 5) + (hash << 7) +
+      (hash << 8) + (hash << 40);
+    hash ^= char_buf[i];
+  }
+  return hash;
+}
+
+inline uint64_t fnv64(const std::string& str,
+                      uint64_t hash = FNV_64_HASH_START) {
+  return fnv64_buf(str.data(), str.size(), hash);
+}
+
+inline uint64_t fnva64_buf(const void* buf,
+                           size_t n,
+                           uint64_t hash = FNVA_64_HASH_START) {
+  const uint8_t* char_buf = reinterpret_cast<const uint8_t*>(buf);
+
+  for (size_t i = 0; i < n; ++i) {
+    hash ^= char_buf[i];
+    hash += (hash << 1) + (hash << 4) + (hash << 5) + (hash << 7) +
+            (hash << 8) + (hash << 40);
+  }
+  return hash;
+}
+
+inline uint64_t fnva64(const std::string& str,
+                       uint64_t hash = FNVA_64_HASH_START) {
+  return fnva64_buf(str.data(), str.size(), hash);
+}
+
+/*
+ * Paul Hsieh: http://www.azillionmonkeys.com/qed/hash.html
+ */
+
+#define get16bits(d) folly::loadUnaligned<uint16_t>(d)
+
+inline uint32_t hsieh_hash32_buf(const void* buf, size_t len) {
+  // forcing signed char, since other platforms can use unsigned
+  const unsigned char* s = reinterpret_cast<const unsigned char*>(buf);
+  uint32_t hash = static_cast<uint32_t>(len);
+  uint32_t tmp;
+  size_t rem;
+
+  if (len <= 0 || buf == nullptr) {
+    return 0;
+  }
+
+  rem = len & 3;
+  len >>= 2;
+
+  /* Main loop */
+  for (;len > 0; len--) {
+    hash  += get16bits (s);
+    tmp    = (get16bits (s+2) << 11) ^ hash;
+    hash   = (hash << 16) ^ tmp;
+    s  += 2*sizeof (uint16_t);
+    hash  += hash >> 11;
+  }
+
+  /* Handle end cases */
+  switch (rem) {
+  case 3:
+    hash += get16bits(s);
+    hash ^= hash << 16;
+    hash ^= s[sizeof (uint16_t)] << 18;
+    hash += hash >> 11;
+    break;
+  case 2:
+    hash += get16bits(s);
+    hash ^= hash << 11;
+    hash += hash >> 17;
+    break;
+  case 1:
+    hash += *s;
+    hash ^= hash << 10;
+    hash += hash >> 1;
+  }
+
+  /* Force "avalanching" of final 127 bits */
+  hash ^= hash << 3;
+  hash += hash >> 5;
+  hash ^= hash << 4;
+  hash += hash >> 17;
+  hash ^= hash << 25;
+  hash += hash >> 6;
+
+  return hash;
+};
+
+#undef get16bits
+
+inline uint32_t hsieh_hash32(const char* s) {
+  return hsieh_hash32_buf(s, std::strlen(s));
+}
+
+inline uint32_t hsieh_hash32_str(const std::string& str) {
+  return hsieh_hash32_buf(str.data(), str.size());
+}
+
+//////////////////////////////////////////////////////////////////////
+
+} // namespace hash
+
+namespace detail {
+struct integral_hasher {
+  template <typename I>
+  size_t operator()(I const& i) const {
+    static_assert(sizeof(I) <= 8, "input type is too wide");
+    if (sizeof(I) <= 4) { // the branch taken is known at compile time
+      auto const i32 = static_cast<int32_t>(i); // impl accident: sign-extends
+      auto const u32 = static_cast<uint32_t>(i32);
+      return static_cast<size_t>(hash::jenkins_rev_mix32(u32));
+    } else {
+      auto const u64 = static_cast<uint64_t>(i);
+      return static_cast<size_t>(hash::twang_mix64(u64));
+    }
+  }
+};
+} // namespace detail
+
+template <class Key, class Enable = void>
+struct hasher;
+
+struct Hash {
+  template <class T>
+  size_t operator()(const T& v) const {
+    return hasher<T>()(v);
+  }
+
+  template <class T, class... Ts>
+  size_t operator()(const T& t, const Ts&... ts) const {
+    return hash::hash_128_to_64((*this)(t), (*this)(ts...));
+  }
+};
+
+template <>
+struct hasher<bool> {
+  size_t operator()(bool key) const {
+    // Make sure that all the output bits depend on the input.
+    return key ? std::numeric_limits<size_t>::max() : 0;
+  }
+};
+
+template <>
+struct hasher<unsigned long long> : detail::integral_hasher {};
+
+template <>
+struct hasher<signed long long> : detail::integral_hasher {};
+
+template <>
+struct hasher<unsigned long> : detail::integral_hasher {};
+
+template <>
+struct hasher<signed long> : detail::integral_hasher {};
+
+template <>
+struct hasher<unsigned int> : detail::integral_hasher {};
+
+template <>
+struct hasher<signed int> : detail::integral_hasher {};
+
+template <>
+struct hasher<unsigned short> : detail::integral_hasher {};
+
+template <>
+struct hasher<signed short> : detail::integral_hasher {};
+
+template <>
+struct hasher<unsigned char> : detail::integral_hasher {};
+
+template <>
+struct hasher<signed char> : detail::integral_hasher {};
+
+template <> // char is a different type from both signed char and unsigned char
+struct hasher<char> : detail::integral_hasher {};
+
+template <> struct hasher<std::string> {
+  size_t operator()(const std::string& key) const {
+    return static_cast<size_t>(
+        hash::SpookyHashV2::Hash64(key.data(), key.size(), 0));
+  }
+};
+
+template <class T>
+struct hasher<T, typename std::enable_if<std::is_enum<T>::value, void>::type> {
+  size_t operator()(T key) const {
+    return Hash()(static_cast<typename std::underlying_type<T>::type>(key));
+  }
+};
+
+template <class T1, class T2>
+struct hasher<std::pair<T1, T2>> {
+  size_t operator()(const std::pair<T1, T2>& key) const {
+    return Hash()(key.first, key.second);
+  }
+};
+
+template <typename... Ts>
+struct hasher<std::tuple<Ts...>> {
+  size_t operator() (const std::tuple<Ts...>& key) const {
+    return applyTuple(Hash(), key);
+  }
+};
+
+// 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.
+namespace std {
+  // Hash function for pairs. Requires default hash functions for both
+  // items in the pair.
+  template <typename T1, typename T2>
+  struct hash<std::pair<T1, T2> > {
+   public:
+    size_t operator()(const std::pair<T1, T2>& x) const {
+      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
diff --git a/folly/IPAddressV4.h b/folly/IPAddressV4.h
index 76534add..96de8add 100644
--- a/folly/IPAddressV4.h
+++ b/folly/IPAddressV4.h
@@ -23,9 +23,9 @@
 #include <iosfwd>
 
 #include <folly/FBString.h>
+#include <folly/Hash.h>
 #include <folly/Range.h>
 #include <folly/detail/IPAddress.h>
-#include <folly/hash/Hash.h>
 
 namespace folly {
 
diff --git a/folly/IPAddressV6.h b/folly/IPAddressV6.h
index 78ec4c76..f641bdcd 100644
--- a/folly/IPAddressV6.h
+++ b/folly/IPAddressV6.h
@@ -25,10 +25,10 @@
 #include <stdexcept>
 
 #include <folly/FBString.h>
+#include <folly/Hash.h>
 #include <folly/Optional.h>
 #include <folly/Range.h>
 #include <folly/detail/IPAddress.h>
-#include <folly/hash/Hash.h>
 
 namespace folly {
 
diff --git a/folly/Makefile.am b/folly/Makefile.am
index 439ea6b8..ce29ac05 100644
--- a/folly/Makefile.am
+++ b/folly/Makefile.am
@@ -229,7 +229,6 @@ nobase_follyinclude_HEADERS = \
 	futures/test/TestExecutor.h \
 	hash/Checksum.h \
 	hash/detail/ChecksumDetail.h \
-	hash/Hash.h \
 	hash/SpookyHashV1.h \
 	hash/SpookyHashV2.h \
 	gen/Base.h \
@@ -247,6 +246,7 @@ nobase_follyinclude_HEADERS = \
 	gen/String.h \
 	gen/String-inl.h \
 	GroupVarint.h \
+	Hash.h \
 	IPAddress.h \
 	IPAddressV4.h \
 	IPAddressV6.h \
diff --git a/folly/Singleton.h b/folly/Singleton.h
index 413b51f8..028cf7f1 100644
--- a/folly/Singleton.h
+++ b/folly/Singleton.h
@@ -125,12 +125,12 @@
 #include <folly/Demangle.h>
 #include <folly/Exception.h>
 #include <folly/Executor.h>
+#include <folly/Hash.h>
 #include <folly/Memory.h>
 #include <folly/RWSpinLock.h>
 #include <folly/Synchronized.h>
 #include <folly/detail/StaticSingletonManager.h>
 #include <folly/experimental/ReadMostlySharedPtr.h>
-#include <folly/hash/Hash.h>
 
 #include <algorithm>
 #include <atomic>
diff --git a/folly/SocketAddress.cpp b/folly/SocketAddress.cpp
index af6cd77f..6cb5a7a0 100644
--- a/folly/SocketAddress.cpp
+++ b/folly/SocketAddress.cpp
@@ -32,7 +32,7 @@
 #include <folly/CppAttributes.h>
 #include <folly/Exception.h>
 #include <folly/Format.h>
-#include <folly/hash/Hash.h>
+#include <folly/Hash.h>
 
 namespace {
 
diff --git a/folly/Uri-inl.h b/folly/Uri-inl.h
index 50d57c2e..6445eef3 100644
--- a/folly/Uri-inl.h
+++ b/folly/Uri-inl.h
@@ -22,7 +22,7 @@
 #include <tuple>
 
 #include <folly/Conv.h>
-#include <folly/hash/Hash.h>
+#include <folly/Hash.h>
 
 namespace folly {
 
diff --git a/folly/concurrency/CacheLocality.h b/folly/concurrency/CacheLocality.h
index ecbed1ef..38f5557c 100644
--- a/folly/concurrency/CacheLocality.h
+++ b/folly/concurrency/CacheLocality.h
@@ -28,12 +28,12 @@
 #include <unordered_map>
 #include <vector>
 
+#include <folly/Hash.h>
 #include <folly/Indestructible.h>
 #include <folly/Likely.h>
 #include <folly/Memory.h>
 #include <folly/Portability.h>
 #include <folly/ThreadId.h>
-#include <folly/hash/Hash.h>
 #include <folly/portability/BitsFunctexcept.h>
 #include <folly/portability/Memory.h>
 
diff --git a/folly/concurrency/test/ConcurrentHashMapTest.cpp b/folly/concurrency/test/ConcurrentHashMapTest.cpp
index 32b3d8ae..cf283c41 100644
--- a/folly/concurrency/test/ConcurrentHashMapTest.cpp
+++ b/folly/concurrency/test/ConcurrentHashMapTest.cpp
@@ -17,8 +17,8 @@
 #include <memory>
 #include <thread>
 
+#include <folly/Hash.h>
 #include <folly/concurrency/ConcurrentHashMap.h>
-#include <folly/hash/Hash.h>
 #include <folly/portability/GTest.h>
 #include <folly/test/DeterministicSchedule.h>
 
diff --git a/folly/detail/Futex.cpp b/folly/detail/Futex.cpp
index da7a04dc..8604a745 100644
--- a/folly/detail/Futex.cpp
+++ b/folly/detail/Futex.cpp
@@ -16,8 +16,8 @@
 
 #include <folly/detail/Futex.h>
 #include <boost/intrusive/list.hpp>
+#include <folly/Hash.h>
 #include <folly/ScopeGuard.h>
-#include <folly/hash/Hash.h>
 #include <folly/portability/SysSyscall.h>
 #include <stdint.h>
 #include <string.h>
diff --git a/folly/detail/MemoryIdler.h b/folly/detail/MemoryIdler.h
index fc7c8b7e..fcbde002 100644
--- a/folly/detail/MemoryIdler.h
+++ b/folly/detail/MemoryIdler.h
@@ -20,10 +20,10 @@
 #include <chrono>
 
 #include <folly/AtomicStruct.h>
+#include <folly/Hash.h>
 #include <folly/ThreadId.h>
 #include <folly/Traits.h>
 #include <folly/detail/Futex.h>
-#include <folly/hash/Hash.h>
 
 namespace folly {
 
diff --git a/folly/dynamic.cpp b/folly/dynamic.cpp
index 3ac1173b..08e97472 100644
--- a/folly/dynamic.cpp
+++ b/folly/dynamic.cpp
@@ -18,7 +18,7 @@
 
 #include <folly/Assume.h>
 #include <folly/Format.h>
-#include <folly/hash/Hash.h>
+#include <folly/Hash.h>
 #include <folly/portability/BitsFunctexcept.h>
 
 namespace folly {
diff --git a/folly/experimental/FunctionScheduler.h b/folly/experimental/FunctionScheduler.h
index e8765fab..fbc73993 100644
--- a/folly/experimental/FunctionScheduler.h
+++ b/folly/experimental/FunctionScheduler.h
@@ -18,13 +18,13 @@
 
 #include <folly/Function.h>
 #include <folly/Range.h>
-#include <folly/hash/Hash.h>
+#include <folly/Hash.h>
 #include <chrono>
 #include <condition_variable>
 #include <mutex>
 #include <thread>
-#include <unordered_map>
 #include <vector>
+#include <unordered_map>
 
 namespace folly {
 
diff --git a/folly/experimental/StringKeyedUnorderedMap.h b/folly/experimental/StringKeyedUnorderedMap.h
index 4cf33b43..41180cb7 100644
--- a/folly/experimental/StringKeyedUnorderedMap.h
+++ b/folly/experimental/StringKeyedUnorderedMap.h
@@ -24,9 +24,9 @@
 #include <unordered_map>
 #include <utility>
 
+#include <folly/Hash.h>
 #include <folly/Range.h>
 #include <folly/experimental/StringKeyedCommon.h>
-#include <folly/hash/Hash.h>
 
 namespace folly {
 
diff --git a/folly/experimental/StringKeyedUnorderedSet.h b/folly/experimental/StringKeyedUnorderedSet.h
index 269d2e6d..11317ede 100644
--- a/folly/experimental/StringKeyedUnorderedSet.h
+++ b/folly/experimental/StringKeyedUnorderedSet.h
@@ -24,9 +24,9 @@
 #include <unordered_set>
 #include <utility>
 
+#include <folly/Hash.h>
 #include <folly/Range.h>
 #include <folly/experimental/StringKeyedCommon.h>
-#include <folly/hash/Hash.h>
 
 namespace folly {
 
diff --git a/folly/experimental/symbolizer/ElfCache.h b/folly/experimental/symbolizer/ElfCache.h
index 57a36cf7..b9d7d966 100644
--- a/folly/experimental/symbolizer/ElfCache.h
+++ b/folly/experimental/symbolizer/ElfCache.h
@@ -29,9 +29,9 @@
 #include <boost/operators.hpp>
 #include <glog/logging.h>
 
+#include <folly/Hash.h>
 #include <folly/Range.h>
 #include <folly/experimental/symbolizer/Elf.h>
-#include <folly/hash/Hash.h>
 
 namespace folly {
 namespace symbolizer {
diff --git a/folly/experimental/test/StringKeyedTest.cpp b/folly/experimental/test/StringKeyedTest.cpp
index 072500b5..b6744459 100644
--- a/folly/experimental/test/StringKeyedTest.cpp
+++ b/folly/experimental/test/StringKeyedTest.cpp
@@ -25,8 +25,8 @@
 
 #include <glog/logging.h>
 
+#include <folly/Hash.h>
 #include <folly/Range.h>
-#include <folly/hash/Hash.h>
 #include <folly/portability/GFlags.h>
 #include <folly/portability/GTest.h>
 
diff --git a/folly/hash/Hash.h b/folly/hash/Hash.h
deleted file mode 100644
index 410d2720..00000000
--- a/folly/hash/Hash.h
+++ /dev/null
@@ -1,519 +0,0 @@
-/*
- * Copyright 2017 Facebook, Inc.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *   http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#pragma once
-
-#include <cstdint>
-#include <cstring>
-#include <limits>
-#include <string>
-#include <tuple>
-#include <type_traits>
-#include <utility>
-
-#include <folly/ApplyTuple.h>
-#include <folly/Bits.h>
-#include <folly/hash/SpookyHashV1.h>
-#include <folly/hash/SpookyHashV2.h>
-
-/*
- * Various hashing functions.
- */
-
-namespace folly { namespace hash {
-
-// This is a general-purpose way to create a single hash from multiple
-// 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.
-
-
-// This is the Hash128to64 function from Google's cityhash (available
-// under the MIT License).  We use it to reduce multiple 64 bit hashes
-// into a single hash.
-inline uint64_t hash_128_to_64(const uint64_t upper, const uint64_t lower) {
-  // Murmur-inspired hashing.
-  const uint64_t kMul = 0x9ddfea08eb382d69ULL;
-  uint64_t a = (lower ^ upper) * kMul;
-  a ^= (a >> 47);
-  uint64_t b = (upper ^ a) * kMul;
-  b ^= (b >> 47);
-  b *= kMul;
-  return b;
-}
-
-// 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;
-}
-
-inline uint32_t twang_32from64(uint64_t key);
-
-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_generic<Hasher>(ts...);
-  /* static */ if (sizeof(size_t) == sizeof(uint32_t)) {
-    return twang_32from64((uint64_t(seed) << 32) | remainder);
-  } else {
-    return static_cast<size_t>(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...);
-}
-
-//////////////////////////////////////////////////////////////////////
-
-/*
- * Thomas Wang 64 bit mix hash function
- */
-
-inline uint64_t twang_mix64(uint64_t key) {
-  key = (~key) + (key << 21);  // key *= (1 << 21) - 1; key -= 1;
-  key = key ^ (key >> 24);
-  key = key + (key << 3) + (key << 8);  // key *= 1 + (1 << 3) + (1 << 8)
-  key = key ^ (key >> 14);
-  key = key + (key << 2) + (key << 4);  // key *= 1 + (1 << 2) + (1 << 4)
-  key = key ^ (key >> 28);
-  key = key + (key << 31);  // key *= 1 + (1 << 31)
-  return key;
-}
-
-/*
- * Inverse of twang_mix64
- *
- * Note that twang_unmix64 is significantly slower than twang_mix64.
- */
-
-inline uint64_t twang_unmix64(uint64_t key) {
-  // See the comments in jenkins_rev_unmix32 for an explanation as to how this
-  // was generated
-  key *= 4611686016279904257U;
-  key ^= (key >> 28) ^ (key >> 56);
-  key *= 14933078535860113213U;
-  key ^= (key >> 14) ^ (key >> 28) ^ (key >> 42) ^ (key >> 56);
-  key *= 15244667743933553977U;
-  key ^= (key >> 24) ^ (key >> 48);
-  key = (key + 1) * 9223367638806167551U;
-  return key;
-}
-
-/*
- * Thomas Wang downscaling hash function
- */
-
-inline uint32_t twang_32from64(uint64_t key) {
-  key = (~key) + (key << 18);
-  key = key ^ (key >> 31);
-  key = key * 21;
-  key = key ^ (key >> 11);
-  key = key + (key << 6);
-  key = key ^ (key >> 22);
-  return (uint32_t) key;
-}
-
-/*
- * Robert Jenkins' reversible 32 bit mix hash function
- */
-
-inline uint32_t jenkins_rev_mix32(uint32_t key) {
-  key += (key << 12);  // key *= (1 + (1 << 12))
-  key ^= (key >> 22);
-  key += (key << 4);   // key *= (1 + (1 << 4))
-  key ^= (key >> 9);
-  key += (key << 10);  // key *= (1 + (1 << 10))
-  key ^= (key >> 2);
-  // key *= (1 + (1 << 7)) * (1 + (1 << 12))
-  key += (key << 7);
-  key += (key << 12);
-  return key;
-}
-
-/*
- * Inverse of jenkins_rev_mix32
- *
- * Note that jenkinks_rev_unmix32 is significantly slower than
- * jenkins_rev_mix32.
- */
-
-inline uint32_t jenkins_rev_unmix32(uint32_t key) {
-  // These are the modular multiplicative inverses (in Z_2^32) of the
-  // multiplication factors in jenkins_rev_mix32, in reverse order.  They were
-  // computed using the Extended Euclidean algorithm, see
-  // http://en.wikipedia.org/wiki/Modular_multiplicative_inverse
-  key *= 2364026753U;
-
-  // The inverse of a ^= (a >> n) is
-  // b = a
-  // for (int i = n; i < 32; i += n) {
-  //   b ^= (a >> i);
-  // }
-  key ^=
-    (key >> 2) ^ (key >> 4) ^ (key >> 6) ^ (key >> 8) ^
-    (key >> 10) ^ (key >> 12) ^ (key >> 14) ^ (key >> 16) ^
-    (key >> 18) ^ (key >> 20) ^ (key >> 22) ^ (key >> 24) ^
-    (key >> 26) ^ (key >> 28) ^ (key >> 30);
-  key *= 3222273025U;
-  key ^= (key >> 9) ^ (key >> 18) ^ (key >> 27);
-  key *= 4042322161U;
-  key ^= (key >> 22);
-  key *= 16773121U;
-  return key;
-}
-
-/*
- * Fowler / Noll / Vo (FNV) Hash
- *     http://www.isthe.com/chongo/tech/comp/fnv/
- */
-
-const uint32_t FNV_32_HASH_START = 2166136261UL;
-const uint64_t FNV_64_HASH_START = 14695981039346656037ULL;
-const uint64_t FNVA_64_HASH_START = 14695981039346656037ULL;
-
-inline uint32_t fnv32(const char* buf, uint32_t hash = FNV_32_HASH_START) {
-  // forcing signed char, since other platforms can use unsigned
-  const signed char* s = reinterpret_cast<const signed char*>(buf);
-
-  for (; *s; ++s) {
-    hash += (hash << 1) + (hash << 4) + (hash << 7) +
-            (hash << 8) + (hash << 24);
-    hash ^= *s;
-  }
-  return hash;
-}
-
-inline uint32_t fnv32_buf(const void* buf,
-                          size_t n,
-                          uint32_t hash = FNV_32_HASH_START) {
-  // forcing signed char, since other platforms can use unsigned
-  const signed char* char_buf = reinterpret_cast<const signed char*>(buf);
-
-  for (size_t i = 0; i < n; ++i) {
-    hash += (hash << 1) + (hash << 4) + (hash << 7) +
-            (hash << 8) + (hash << 24);
-    hash ^= char_buf[i];
-  }
-
-  return hash;
-}
-
-inline uint32_t fnv32(const std::string& str,
-                      uint32_t hash = FNV_32_HASH_START) {
-  return fnv32_buf(str.data(), str.size(), hash);
-}
-
-inline uint64_t fnv64(const char* buf, uint64_t hash = FNV_64_HASH_START) {
-  // forcing signed char, since other platforms can use unsigned
-  const signed char* s = reinterpret_cast<const signed char*>(buf);
-
-  for (; *s; ++s) {
-    hash += (hash << 1) + (hash << 4) + (hash << 5) + (hash << 7) +
-      (hash << 8) + (hash << 40);
-    hash ^= *s;
-  }
-  return hash;
-}
-
-inline uint64_t fnv64_buf(const void* buf,
-                          size_t n,
-                          uint64_t hash = FNV_64_HASH_START) {
-  // forcing signed char, since other platforms can use unsigned
-  const signed char* char_buf = reinterpret_cast<const signed char*>(buf);
-
-  for (size_t i = 0; i < n; ++i) {
-    hash += (hash << 1) + (hash << 4) + (hash << 5) + (hash << 7) +
-      (hash << 8) + (hash << 40);
-    hash ^= char_buf[i];
-  }
-  return hash;
-}
-
-inline uint64_t fnv64(const std::string& str,
-                      uint64_t hash = FNV_64_HASH_START) {
-  return fnv64_buf(str.data(), str.size(), hash);
-}
-
-inline uint64_t fnva64_buf(const void* buf,
-                           size_t n,
-                           uint64_t hash = FNVA_64_HASH_START) {
-  const uint8_t* char_buf = reinterpret_cast<const uint8_t*>(buf);
-
-  for (size_t i = 0; i < n; ++i) {
-    hash ^= char_buf[i];
-    hash += (hash << 1) + (hash << 4) + (hash << 5) + (hash << 7) +
-            (hash << 8) + (hash << 40);
-  }
-  return hash;
-}
-
-inline uint64_t fnva64(const std::string& str,
-                       uint64_t hash = FNVA_64_HASH_START) {
-  return fnva64_buf(str.data(), str.size(), hash);
-}
-
-/*
- * Paul Hsieh: http://www.azillionmonkeys.com/qed/hash.html
- */
-
-#define get16bits(d) folly::loadUnaligned<uint16_t>(d)
-
-inline uint32_t hsieh_hash32_buf(const void* buf, size_t len) {
-  // forcing signed char, since other platforms can use unsigned
-  const unsigned char* s = reinterpret_cast<const unsigned char*>(buf);
-  uint32_t hash = static_cast<uint32_t>(len);
-  uint32_t tmp;
-  size_t rem;
-
-  if (len <= 0 || buf == nullptr) {
-    return 0;
-  }
-
-  rem = len & 3;
-  len >>= 2;
-
-  /* Main loop */
-  for (;len > 0; len--) {
-    hash  += get16bits (s);
-    tmp    = (get16bits (s+2) << 11) ^ hash;
-    hash   = (hash << 16) ^ tmp;
-    s  += 2*sizeof (uint16_t);
-    hash  += hash >> 11;
-  }
-
-  /* Handle end cases */
-  switch (rem) {
-  case 3:
-    hash += get16bits(s);
-    hash ^= hash << 16;
-    hash ^= s[sizeof (uint16_t)] << 18;
-    hash += hash >> 11;
-    break;
-  case 2:
-    hash += get16bits(s);
-    hash ^= hash << 11;
-    hash += hash >> 17;
-    break;
-  case 1:
-    hash += *s;
-    hash ^= hash << 10;
-    hash += hash >> 1;
-  }
-
-  /* Force "avalanching" of final 127 bits */
-  hash ^= hash << 3;
-  hash += hash >> 5;
-  hash ^= hash << 4;
-  hash += hash >> 17;
-  hash ^= hash << 25;
-  hash += hash >> 6;
-
-  return hash;
-};
-
-#undef get16bits
-
-inline uint32_t hsieh_hash32(const char* s) {
-  return hsieh_hash32_buf(s, std::strlen(s));
-}
-
-inline uint32_t hsieh_hash32_str(const std::string& str) {
-  return hsieh_hash32_buf(str.data(), str.size());
-}
-
-//////////////////////////////////////////////////////////////////////
-
-} // namespace hash
-
-namespace detail {
-struct integral_hasher {
-  template <typename I>
-  size_t operator()(I const& i) const {
-    static_assert(sizeof(I) <= 8, "input type is too wide");
-    if (sizeof(I) <= 4) { // the branch taken is known at compile time
-      auto const i32 = static_cast<int32_t>(i); // impl accident: sign-extends
-      auto const u32 = static_cast<uint32_t>(i32);
-      return static_cast<size_t>(hash::jenkins_rev_mix32(u32));
-    } else {
-      auto const u64 = static_cast<uint64_t>(i);
-      return static_cast<size_t>(hash::twang_mix64(u64));
-    }
-  }
-};
-} // namespace detail
-
-template <class Key, class Enable = void>
-struct hasher;
-
-struct Hash {
-  template <class T>
-  size_t operator()(const T& v) const {
-    return hasher<T>()(v);
-  }
-
-  template <class T, class... Ts>
-  size_t operator()(const T& t, const Ts&... ts) const {
-    return hash::hash_128_to_64((*this)(t), (*this)(ts...));
-  }
-};
-
-template <>
-struct hasher<bool> {
-  size_t operator()(bool key) const {
-    // Make sure that all the output bits depend on the input.
-    return key ? std::numeric_limits<size_t>::max() : 0;
-  }
-};
-
-template <>
-struct hasher<unsigned long long> : detail::integral_hasher {};
-
-template <>
-struct hasher<signed long long> : detail::integral_hasher {};
-
-template <>
-struct hasher<unsigned long> : detail::integral_hasher {};
-
-template <>
-struct hasher<signed long> : detail::integral_hasher {};
-
-template <>
-struct hasher<unsigned int> : detail::integral_hasher {};
-
-template <>
-struct hasher<signed int> : detail::integral_hasher {};
-
-template <>
-struct hasher<unsigned short> : detail::integral_hasher {};
-
-template <>
-struct hasher<signed short> : detail::integral_hasher {};
-
-template <>
-struct hasher<unsigned char> : detail::integral_hasher {};
-
-template <>
-struct hasher<signed char> : detail::integral_hasher {};
-
-template <> // char is a different type from both signed char and unsigned char
-struct hasher<char> : detail::integral_hasher {};
-
-template <> struct hasher<std::string> {
-  size_t operator()(const std::string& key) const {
-    return static_cast<size_t>(
-        hash::SpookyHashV2::Hash64(key.data(), key.size(), 0));
-  }
-};
-
-template <class T>
-struct hasher<T, typename std::enable_if<std::is_enum<T>::value, void>::type> {
-  size_t operator()(T key) const {
-    return Hash()(static_cast<typename std::underlying_type<T>::type>(key));
-  }
-};
-
-template <class T1, class T2>
-struct hasher<std::pair<T1, T2>> {
-  size_t operator()(const std::pair<T1, T2>& key) const {
-    return Hash()(key.first, key.second);
-  }
-};
-
-template <typename... Ts>
-struct hasher<std::tuple<Ts...>> {
-  size_t operator() (const std::tuple<Ts...>& key) const {
-    return applyTuple(Hash(), key);
-  }
-};
-
-// 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.
-namespace std {
-  // Hash function for pairs. Requires default hash functions for both
-  // items in the pair.
-  template <typename T1, typename T2>
-  struct hash<std::pair<T1, T2> > {
-   public:
-    size_t operator()(const std::pair<T1, T2>& x) const {
-      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
diff --git a/folly/hash/test/ChecksumTest.cpp b/folly/hash/test/ChecksumTest.cpp
index 05ac6e59..e5e613c6 100644
--- a/folly/hash/test/ChecksumTest.cpp
+++ b/folly/hash/test/ChecksumTest.cpp
@@ -19,7 +19,7 @@
 #include <boost/crc.hpp>
 
 #include <folly/Benchmark.h>
-#include <folly/hash/Hash.h>
+#include <folly/Hash.h>
 #include <folly/hash/detail/ChecksumDetail.h>
 #include <folly/portability/GFlags.h>
 #include <folly/portability/GTest.h>
diff --git a/folly/io/test/CompressionTest.cpp b/folly/io/test/CompressionTest.cpp
index 69069c82..69a037d8 100644
--- a/folly/io/test/CompressionTest.cpp
+++ b/folly/io/test/CompressionTest.cpp
@@ -27,10 +27,10 @@
 #include <glog/logging.h>
 
 #include <folly/Benchmark.h>
+#include <folly/Hash.h>
 #include <folly/Memory.h>
 #include <folly/Random.h>
 #include <folly/Varint.h>
-#include <folly/hash/Hash.h>
 #include <folly/io/IOBufQueue.h>
 #include <folly/portability/GTest.h>
 
diff --git a/folly/test/AtomicHashArrayTest.cpp b/folly/test/AtomicHashArrayTest.cpp
index 531732c4..780076a1 100644
--- a/folly/test/AtomicHashArrayTest.cpp
+++ b/folly/test/AtomicHashArrayTest.cpp
@@ -20,8 +20,8 @@
 
 #include <folly/AtomicHashArray.h>
 #include <folly/Conv.h>
+#include <folly/Hash.h>
 #include <folly/Memory.h>
-#include <folly/hash/Hash.h>
 #include <folly/portability/GTest.h>
 #include <folly/portability/SysMman.h>
 
diff --git a/folly/test/ConcurrentSkipListBenchmark.cpp b/folly/test/ConcurrentSkipListBenchmark.cpp
index 97c27620..cfe9aa98 100644
--- a/folly/test/ConcurrentSkipListBenchmark.cpp
+++ b/folly/test/ConcurrentSkipListBenchmark.cpp
@@ -23,8 +23,8 @@
 
 #include <folly/Benchmark.h>
 #include <folly/ConcurrentSkipList.h>
+#include <folly/Hash.h>
 #include <folly/RWSpinLock.h>
-#include <folly/hash/Hash.h>
 #include <folly/portability/GFlags.h>
 #include <glog/logging.h>
 
diff --git a/folly/hash/test/HashBenchmark.cpp b/folly/test/HashBenchmark.cpp
similarity index 99%
rename from folly/hash/test/HashBenchmark.cpp
rename to folly/test/HashBenchmark.cpp
index f387f5a7..4595a6e6 100644
--- a/folly/hash/test/HashBenchmark.cpp
+++ b/folly/test/HashBenchmark.cpp
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#include <folly/hash/Hash.h>
+#include <folly/Hash.h>
 
 #include <stdint.h>
 #include <deque>
diff --git a/folly/hash/test/HashTest.cpp b/folly/test/HashTest.cpp
similarity index 99%
rename from folly/hash/test/HashTest.cpp
rename to folly/test/HashTest.cpp
index fe7a8042..759f9975 100644
--- a/folly/hash/test/HashTest.cpp
+++ b/folly/test/HashTest.cpp
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#include <folly/hash/Hash.h>
+#include <folly/Hash.h>
 #include <folly/MapUtil.h>
 #include <folly/portability/GTest.h>
 #include <stdint.h>
diff --git a/folly/test/Makefile.am b/folly/test/Makefile.am
index 22c1127e..a2f58830 100644
--- a/folly/test/Makefile.am
+++ b/folly/test/Makefile.am
@@ -89,7 +89,7 @@ foreach_benchmark_SOURCES = ForeachBenchmark.cpp
 foreach_benchmark_LDADD = libfollytestmain.la $(top_builddir)/libfollybenchmark.la
 check_PROGRAMS += foreach_benchmark
 
-hash_test_SOURCES = ../hash/test/HashTest.cpp
+hash_test_SOURCES = HashTest.cpp
 hash_test_LDADD = libfollytestmain.la
 
 invoke_test_SOURCES = ../functional/test/InvokeTest.cpp
diff --git a/folly/test/ThreadCachedIntTest.cpp b/folly/test/ThreadCachedIntTest.cpp
index 588aa52e..e09c780f 100644
--- a/folly/test/ThreadCachedIntTest.cpp
+++ b/folly/test/ThreadCachedIntTest.cpp
@@ -23,8 +23,8 @@
 #include <glog/logging.h>
 
 #include <folly/Benchmark.h>
+#include <folly/Hash.h>
 #include <folly/ThreadId.h>
-#include <folly/hash/Hash.h>
 #include <folly/portability/GFlags.h>
 #include <folly/portability/GTest.h>
 
-- 
2.34.1