From 217f0c33da62cb96e12873a8f80a673caefac4c3 Mon Sep 17 00:00:00 2001
From: Justus Winter <4winter@informatik.uni-hamburg.de>
Date: Tue, 24 Nov 2015 01:07:32 +0100
Subject: [PATCH hurd 3/5] libihash: add general purpose hash functions

* libihash/Makefile (SRCS): Add new file.
* libihash/fasthash.c: New file.
* libihash/ihash.h (hurd_ihash_fasthash{32,64}): New prototypes.
---
 libihash/Makefile   |  2 +-
 libihash/fasthash.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 libihash/ihash.h    | 14 ++++++++++
 3 files changed, 91 insertions(+), 1 deletion(-)
 create mode 100644 libihash/fasthash.c

diff --git a/libihash/Makefile b/libihash/Makefile
index 09bb136..eb5d87e 100644
--- a/libihash/Makefile
+++ b/libihash/Makefile
@@ -20,7 +20,7 @@ dir := libihash
 makemode := library
 
 libname := libihash
-SRCS = ihash.c
+SRCS = ihash.c fasthash.c
 installhdrs = ihash.h
 
 OBJS = $(SRCS:.c=.o)
diff --git a/libihash/fasthash.c b/libihash/fasthash.c
new file mode 100644
index 0000000..9295cf1
--- /dev/null
+++ b/libihash/fasthash.c
@@ -0,0 +1,76 @@
+/* The MIT License
+
+   Copyright (C) 2012 Zilong Tan (eric.zltan@gmail.com)
+
+   Permission is hereby granted, free of charge, to any person
+   obtaining a copy of this software and associated documentation
+   files (the "Software"), to deal in the Software without
+   restriction, including without limitation the rights to use, copy,
+   modify, merge, publish, distribute, sublicense, and/or sell copies
+   of the Software, and to permit persons to whom the Software is
+   furnished to do so, subject to the following conditions:
+
+   The above copyright notice and this permission notice shall be
+   included in all copies or substantial portions of the Software.
+
+   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+   MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+   NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+   BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+   ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+   CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+   SOFTWARE.
+*/
+
+#include <stdint.h>
+#include <stdio.h>
+
+// Compression function for Merkle-Damgard construction.
+// This function is generated using the framework provided.
+#define mix(h) ({					\
+			(h) ^= (h) >> 23;		\
+			(h) *= 0x2127599bf4325c37ULL;	\
+			(h) ^= (h) >> 47; })
+
+uint64_t hurd_ihash_fasthash64(const void *buf, size_t len, uint64_t seed)
+{
+	const uint64_t    m = 0x880355f21e6d1965ULL;
+	const uint64_t *pos = (const uint64_t *)buf;
+	const uint64_t *end = pos + (len / 8);
+	const unsigned char *pos2;
+	uint64_t h = seed ^ (len * m);
+	uint64_t v;
+
+	while (pos != end) {
+		v  = *pos++;
+		h ^= mix(v);
+		h *= m;
+	}
+
+	pos2 = (const unsigned char*)pos;
+	v = 0;
+
+	switch (len & 7) {
+	case 7: v ^= (uint64_t)pos2[6] << 48;
+	case 6: v ^= (uint64_t)pos2[5] << 40;
+	case 5: v ^= (uint64_t)pos2[4] << 32;
+	case 4: v ^= (uint64_t)pos2[3] << 24;
+	case 3: v ^= (uint64_t)pos2[2] << 16;
+	case 2: v ^= (uint64_t)pos2[1] << 8;
+	case 1: v ^= (uint64_t)pos2[0];
+		h ^= mix(v);
+		h *= m;
+	}
+
+	return mix(h);
+}
+
+uint32_t hurd_ihash_fasthash32(const void *buf, size_t len, uint32_t seed)
+{
+	// the following trick converts the 64-bit hashcode to Fermat
+	// residue, which shall retain information from both the higher
+	// and lower parts of hashcode.
+        uint64_t h = hurd_ihash_fasthash64(buf, len, seed);
+	return h - (h >> 32);
+}
diff --git a/libihash/ihash.h b/libihash/ihash.h
index 986291b..50676a6 100644
--- a/libihash/ihash.h
+++ b/libihash/ihash.h
@@ -136,6 +136,13 @@ typedef struct hurd_ihash *hurd_ihash_t;
     .max_load = HURD_IHASH_MAX_LOAD_DEFAULT,				\
     .locp_offset = (locp_offs)}
 
+#define HURD_IHASH_INITIALIZER_GKI(locp_offs, cleanup, hash, compare)   \
+  { .nr_items = 0, .size = 0, .cleanup = (cleanup),			\
+    .max_load = HURD_IHASH_MAX_LOAD_DEFAULT,				\
+    .locp_offset = (locp_offs),						\
+    .fct_hash = (hash),							\
+    .fct_cmp = (compare)}						\
+
 /* Initialize the hash table at address HT.  If LOCP_OFFSET is not
    HURD_IHASH_NO_LOCP, then this is an offset (in bytes) from the
    address of a hash value where a location pointer can be found.  The
@@ -339,5 +346,12 @@ int hurd_ihash_remove (hurd_ihash_t ht, hurd_ihash_key_t key);
    was provided to hurd_ihash_add().  This call is faster than
    hurd_ihash_remove().  */
 void hurd_ihash_locp_remove (hurd_ihash_t ht, hurd_ihash_locp_t locp);
+
+/* General purpose hash functions.  */
+
+/* Zilong Tans fast-hash.  Based on 'Marsaglia, George. "Xorshift
+   rngs."  Journal of Statistical Software 8.14 (2003): 1-6.'  */
+uint32_t hurd_ihash_fasthash32 (const void *buf, size_t len, uint32_t seed);
+uint64_t hurd_ihash_fasthash64 (const void *buf, size_t len, uint64_t seed);
 
 #endif	/* _HURD_IHASH_H */
-- 
2.1.4