From 47bb023092521d74b80122f54c15ff2e96dce878 Mon Sep 17 00:00:00 2001
From: Anthony Pesch <inolen@gmail.com>
Date: Tue, 8 Aug 2017 21:32:44 -0400
Subject: [PATCH] initial hashtable implementation

---
 src/core/hash.h | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)
 create mode 100644 src/core/hash.h

diff --git a/src/core/hash.h b/src/core/hash.h
new file mode 100644
index 00000000..aa531998
--- /dev/null
+++ b/src/core/hash.h
@@ -0,0 +1,35 @@
+#ifndef REDREAM_HASH_H
+#define REDREAM_HASH_H
+
+#include "core/list.h"
+#include "core/math.h"
+
+#define DECLARE_HASHTABLE(name, bits) struct list name[1 << bits]
+
+#define HASH_SIZE(name) ARRAY_SIZE(name)
+#define HASH_BITS(name) ctz64(HASH_SIZE(name))
+
+/*
+ * hash method taken from Chuck Lever's paper:
+ * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
+ *
+ * the general idea is to multiply the input by -phi, and since multiplication
+ * propagates changes towards the high order bits, shifting off the low order
+ * bits when less bits are needed
+ *
+ * 2^64 / -PHI = -11400714819323198485.95 = 0x61c8864680b583eb
+ */
+#define GOLDEN_RATIO_64 UINT64_C(0x61c8864680b583eb)
+
+#define hash_key(x, bits) (((uint64_t)(x)*GOLDEN_RATIO_64) >> (64 - bits))
+
+#define hash_bkt(table, key) &table[hash_key((key), HASH_BITS(table))]
+
+#define hash_add(bkt, node) list_add((bkt), (node))
+
+#define hash_del(bkt, node) list_remove((bkt), (node))
+
+#define hash_bkt_for_each_entry(it, bkt, type, member) \
+  list_for_each_entry(it, bkt, type, member)
+
+#endif