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diff --git a/include/fud_hash.hpp b/include/fud_hash.hpp
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+/*
+ * libfud
+ * Copyright 2025 Dominick Allen
+ *
+ * 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.
+ */
+#ifndef FUD_HASH_HPP
+#define FUD_HASH_HPP
+
+#include "fud_string.hpp"
+#include "fud_string_view.hpp"
+#include "fud_utf8.hpp"
+
+#include <type_traits>
+
+/*
+namespace fud {
+template <typename Key>
+concept Hashable = requires(Key key) {
+    { sink.drain(source) } -> std::same_as<DrainResult>;
+};
+} // namespace fud
+*/
+
+namespace fud::detail {
+
+constexpr uint64_t roundToNearest2(uint64_t inputValue) noexcept
+{
+    uint64_t outputValue = inputValue - 1;
+    constexpr uint8_t max2PowerShift = 32;
+    for (uint8_t shift = 1; shift <= max2PowerShift; shift *= 2) {
+        outputValue |= outputValue >> shift;
+    }
+    outputValue++;
+    return outputValue;
+}
+
+/** \brief The djb2 algorithm by Dan Bernstein. See http://www.cse.yorku.ca/~oz/hash.html
+ *
+ * If passed a null pointer for data, returns the initial hash value.
+ */
+size_t djb2(const utf8* data, size_t length);
+
+template <typename T>
+struct DefaultHash {
+    static_assert(std::is_integral_v<T> || std::is_enum_v<T>);
+    size_t operator()(const T& value, size_t seed) const
+    {
+        static_cast<void>(seed);
+        // NOLINTNEXTLINE(cppcoreguidelines-pro-type-reinterpret-cast)
+        return djb2(reinterpret_cast<const utf8*>(&value), sizeof(value));
+    }
+};
+
+template <>
+struct DefaultHash<String> {
+    size_t operator()(const String& value, size_t seed) const;
+};
+
+template <>
+struct DefaultHash<StringView> {
+    size_t operator()(const StringView& value, size_t seed) const;
+};
+
+} // namespace fud::detail
+
+#endif