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+// Copyright 2020 The Abseil Authors
+//
+// 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
+//
+//     https://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.
+//
+// This file provides the Google-internal implementation of the Wyhash
+// algorithm.
+//
+// Wyhash is a fast hash function for hash tables, the fastest we've currently
+// (late 2020) found that passes the SMHasher tests. The algorithm relies on
+// intrinsic 128-bit multiplication for speed. This is not meant to be secure -
+// just fast.
+
+#ifndef ABSL_HASH_INTERNAL_WYHASH_H_
+#define ABSL_HASH_INTERNAL_WYHASH_H_
+
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace hash_internal {
+
+// Hash function for a byte array. A 64-bit seed and a set of five 64-bit
+// integers are hashed into the result.
+//
+// To allow all hashable types (including string_view and Span) to depend on
+// this algoritm, we keep the API low-level, with as few dependencies as
+// possible.
+uint64_t Wyhash(const void* data, size_t len, uint64_t seed,
+                const uint64_t salt[5]);
+
+}  // namespace hash_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_HASH_INTERNAL_WYHASH_H_