v6-0001-Vendor-fasthash.patch

From eca956b55c71a11f39497b60469f13642819c349 Mon Sep 17 00:00:00 2001
From: John Naylor <john.naylor@postgresql.org>
Date: Mon, 27 Nov 2023 17:03:38 +0700
Subject: [PATCH v6 01/13] Vendor fasthash

MIT licensed
---
 src/include/common/hashfn_unstable.h | 80 ++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)
 create mode 100644 src/include/common/hashfn_unstable.h

diff --git a/src/include/common/hashfn_unstable.h b/src/include/common/hashfn_unstable.h
new file mode 100644
index 0000000000..76ed27c0a0
--- /dev/null
+++ b/src/include/common/hashfn_unstable.h
@@ -0,0 +1,80 @@
+/* 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 "fasthash.h"
+
+// Compression function for Merkle-Damgard construction.
+// This function is generated using the framework provided.
+static inline uint64_t mix(uint64_t h) {				
+	h ^= h >> 23;		
+	h *= 0x2127599bf4325c37ULL;
+	h ^= h >> 47;
+	return h;
+}
+
+// security: if the system allows empty keys (len=3) the seed is exposed, the reverse of mix.
+// objsize: 0-1fd: 509
+uint64_t 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);
+} 
+
+// objsize: 0-236: 566
+uint32_t 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 = fasthash64(buf, len, seed);
+	return h - (h >> 32);
+}
-- 
2.43.0