From 573c79fd56715b8f7350db4b6bcaa02b2dda16ee Mon Sep 17 00:00:00 2001
From: Zhe Weng <wengzhe@xiaomi.com>
Date: Tue, 20 Dec 2022 11:02:23 +0800
Subject: [PATCH] hashtable.h: Added a hashtable implementation

Signed-off-by: Zhe Weng <wengzhe@xiaomi.com>
---
 include/nuttx/hashtable.h | 100 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)
 create mode 100644 include/nuttx/hashtable.h

diff --git a/include/nuttx/hashtable.h b/include/nuttx/hashtable.h
new file mode 100644
index 0000000000..bf946ddd0a
--- /dev/null
+++ b/include/nuttx/hashtable.h
@@ -0,0 +1,100 @@
+/****************************************************************************
+ * include/nuttx/hashtable.h
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you 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 __INCLUDE_NUTTX_HASHTABLE_H
+#define __INCLUDE_NUTTX_HASHTABLE_H
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/lib/math32.h>
+#include <nuttx/nuttx.h>
+#include <nuttx/queue.h>
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+/* Hash function related definitions. */
+
+#define GOLDEN_RATIO_32 0x61C88647 /* Negative golden ratio, used by Linux. */
+#define HASH(val, bits) ((uint32_t)((val) * GOLDEN_RATIO_32) >> (32 - (bits)))
+
+/* Hashtable related definitions. */
+
+#define DECLARE_HASHTABLE(table, bits) hash_head_t table[1 << (bits)]
+
+#define hashtable_size(table) (sizeof(table) / sizeof((table)[0]))
+#define hashtable_bits(table) (LOG2_FLOOR(hashtable_size(table)))
+
+#define hashtable_init(table) \
+  do \
+    { \
+      int i; \
+      for (i = 0; i < hashtable_size(table); i++) \
+        { \
+          dq_init(&table[i]); \
+        } \
+    } \
+  while(0)
+
+#define hashtable_add(table, item, key) \
+  dq_addfirst(item, &table[HASH(key, hashtable_bits(table))])
+
+#define hashtable_delete(table, item, key) \
+  dq_rem(item, &table[HASH(key, hashtable_bits(table))])
+
+/* Iterate over whole hashtable. */
+
+#define hashtable_for_every(table, item, i)         \
+  for ((i) = 0; (i) < hashtable_size(table); (i)++) \
+    sq_for_every(&table[i], item)
+
+#define hashtable_for_every_safe(table, item, temp, i) \
+  for ((i) = 0; (i) < hashtable_size(table); (i)++)    \
+    sq_for_every_safe(&table[i], item, temp)
+
+/* Iterate over all possible objects hashing to the same bucket. */
+
+#define hashtable_for_every_possible(table, item, key) \
+  sq_for_every(&table[HASH(key, hashtable_bits(table))], item)
+
+#define hashtable_for_every_possible_safe(table, item, temp, key) \
+  sq_for_every_safe(&table[HASH(key, hashtable_bits(table))], item, temp)
+
+/****************************************************************************
+ * Public Types
+ ****************************************************************************/
+
+/* Note: Our `list` is not suitable for hashtable, because `list` will always
+ * access `head` when iterating by `for_every`, but `head` may sometimes be
+ * accessed by hash result, then hash function will be called on each
+ * iteration. So we use `dq` instead to avoid this.
+ *
+ * Note: There is an optimized type `hlist` on Linux, which saves one pointer
+ * in list head, we can do the same optimization to save memory (but only
+ * saves a little compares to the whole hashtable).
+ */
+
+typedef dq_queue_t hash_head_t;
+typedef dq_entry_t hash_node_t;
+
+#endif /* __INCLUDE_NUTTX_HASHTABLE_H */