From cb9fa588ba8144fcdd52ba4b83d69d93fb18066f Mon Sep 17 00:00:00 2001
From: Dominick Allen <djallen@librehumanitas.org>
Date: Sun, 30 Mar 2025 23:08:43 -0500
Subject: Add hash map.

---
 source/fud_hash.cpp | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 source/fud_hash.cpp

(limited to 'source/fud_hash.cpp')

diff --git a/source/fud_hash.cpp b/source/fud_hash.cpp
new file mode 100644
index 0000000..faa62ff
--- /dev/null
+++ b/source/fud_hash.cpp
@@ -0,0 +1,53 @@
+/*
+ * 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.
+ */
+
+#include "fud_hash.hpp"
+
+namespace fud::detail {
+
+size_t djb2(const utf8* data, size_t length)
+{
+    /* Allegedly djb chose 5381 after testing showed fewer collisions and better avalanching: see
+     * https://stackoverflow.com/questions/10696223/reason-for-the-number-5381-in-the-djb-hash-function */
+    constexpr size_t hashInit = 5381;
+    constexpr size_t mulBy = 33;
+    size_t hash = hashInit;
+    if (data == nullptr) {
+        return hash;
+    }
+
+    for (size_t index = 0; index < length; ++index) {
+        hash = (hash * mulBy) ^ data[index];
+    }
+
+    return hash;
+}
+
+
+size_t DefaultHash<String>::operator()(const String& value, size_t seed) const
+{
+        static_cast<void>(seed);
+        return djb2(value.data(), value.length());
+}
+
+size_t DefaultHash<StringView>::operator()(const StringView& value, size_t seed) const
+{
+        static_cast<void>(seed);
+        return djb2(value.data(), value.length());
+}
+
+}
-- 
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