From 9907b61c574baf0747747f1c512f7cdd88ebed25 Mon Sep 17 00:00:00 2001
From: KunoiSayami <i@leanhe.dev>
Date: Tue, 9 Nov 2021 22:00:01 +0800
Subject: init

---
 util/hash.cc | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 util/hash.cc

(limited to 'util/hash.cc')

diff --git a/util/hash.cc b/util/hash.cc
new file mode 100644
index 0000000..8122fa8
--- /dev/null
+++ b/util/hash.cc
@@ -0,0 +1,55 @@
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+#include "util/hash.h"
+
+#include <cstring>
+
+#include "util/coding.h"
+
+// The FALLTHROUGH_INTENDED macro can be used to annotate implicit fall-through
+// between switch labels. The real definition should be provided externally.
+// This one is a fallback version for unsupported compilers.
+#ifndef FALLTHROUGH_INTENDED
+#define FALLTHROUGH_INTENDED \
+  do {                       \
+  } while (0)
+#endif
+
+namespace leveldb {
+
+uint32_t Hash(const char* data, size_t n, uint32_t seed) {
+  // Similar to murmur hash
+  const uint32_t m = 0xc6a4a793;
+  const uint32_t r = 24;
+  const char* limit = data + n;
+  uint32_t h = seed ^ (n * m);
+
+  // Pick up four bytes at a time
+  while (data + 4 <= limit) {
+    uint32_t w = DecodeFixed32(data);
+    data += 4;
+    h += w;
+    h *= m;
+    h ^= (h >> 16);
+  }
+
+  // Pick up remaining bytes
+  switch (limit - data) {
+    case 3:
+      h += static_cast<uint8_t>(data[2]) << 16;
+      FALLTHROUGH_INTENDED;
+    case 2:
+      h += static_cast<uint8_t>(data[1]) << 8;
+      FALLTHROUGH_INTENDED;
+    case 1:
+      h += static_cast<uint8_t>(data[0]);
+      h *= m;
+      h ^= (h >> r);
+      break;
+  }
+  return h;
+}
+
+}  // namespace leveldb
-- 
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