Added new tensorflow::gtl::FlatMap and tensorflow::gtl::FlatSet classes.

Mostly drop-in replacements for std::unordered_map and std::unordered_set,
but much faster (does not do an allocation per entry, and represents
entries in groups of 8 in a flat array, which is much more cache efficient).

Benchmarks not included in this cl show about 3X to 5X performance
improvements over the std::unordered_{set,map} for many kinds of
common maps e.g. std::unordered_mapmap<int64, int64> or
std::unordered_map<string, int64>.
Change: 137401863

1 files changed, 18 insertions, 0 deletions

diff --git a/tensorflow/core/lib/hash/hash.h b/tensorflow/core/lib/hash/hash.h
index 3c71e7d6cc..4e64c90d62 100644
--- a/tensorflow/core/lib/hash/hash.h
+++ b/tensorflow/core/lib/hash/hash.h
@@ -42,6 +42,24 @@ inline uint64 Hash64Combine(uint64 a, uint64 b) {
   return a ^ (b + 0x9e3779b97f4a7800ULL + (a << 10) + (a >> 4));
 }
 
+// Convenience Hash functors
+struct HashInt64 {
+  size_t operator()(int64 x) const { return static_cast<size_t>(x); }
+};
+struct HashStr {
+  size_t operator()(const string& s) const {
+    return static_cast<size_t>(Hash64(s));
+  }
+};
+template <typename PTR>
+struct HashPtr {
+  size_t operator()(const PTR p) const {
+    // Hash pointers as integers, but bring more entropy to the lower bits.
+    size_t k = static_cast<size_t>(reinterpret_cast<uintptr_t>(p));
+    return k + (k >> 6);
+  }
+};
+
 }  // namespace tensorflow
 
 #endif  // TENSORFLOW_LIB_HASH_HASH_H_