From: Jesper Dangaard Brouer <brouer@redhat.com>
Date: Thu, 25 Jan 2018 19:24:33 +0000 (+0100)
Subject: ebpf: add Paul Hsieh's (LGPL 2.1) hash function SuperFastHash
X-Git-Tag: suricata-4.1.0-beta1~178
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=460a0a6977614a521ebb17cc8e531c6528ff8c69;p=thirdparty%2Fsuricata.git

ebpf: add Paul Hsieh's (LGPL 2.1) hash function SuperFastHash

Adjusted function call API to take an initval. This allow the API
user to set the initial value, as a seed. This could also be used for
inputting the previous hash.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---

diff --git a/ebpf/hash_func01.h b/ebpf/hash_func01.h
new file mode 100644
index 0000000000..060346f67a
--- /dev/null
+++ b/ebpf/hash_func01.h
@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: LGPL-2.1
+ *
+ * Based on Paul Hsieh's (LGPG 2.1) hash function
+ * From: http://www.azillionmonkeys.com/qed/hash.html
+ */
+
+#define get16bits(d) (*((const uint16_t *) (d)))
+
+static __always_inline
+uint32_t SuperFastHash (const char *data, int len, uint32_t initval) {
+	uint32_t hash = initval;
+	uint32_t tmp;
+	int rem;
+
+	if (len <= 0 || data == NULL) return 0;
+
+	rem = len & 3;
+	len >>= 2;
+
+	/* Main loop */
+#pragma clang loop unroll(full)
+	for (;len > 0; len--) {
+		hash  += get16bits (data);
+		tmp    = (get16bits (data+2) << 11) ^ hash;
+		hash   = (hash << 16) ^ tmp;
+		data  += 2*sizeof (uint16_t);
+		hash  += hash >> 11;
+	}
+
+	/* Handle end cases */
+	switch (rem) {
+        case 3: hash += get16bits (data);
+                hash ^= hash << 16;
+                hash ^= ((signed char)data[sizeof (uint16_t)]) << 18;
+                hash += hash >> 11;
+                break;
+        case 2: hash += get16bits (data);
+                hash ^= hash << 11;
+                hash += hash >> 17;
+                break;
+        case 1: hash += (signed char)*data;
+                hash ^= hash << 10;
+                hash += hash >> 1;
+	}
+
+	/* Force "avalanching" of final 127 bits */
+	hash ^= hash << 3;
+	hash += hash >> 5;
+	hash ^= hash << 4;
+	hash += hash >> 17;
+	hash ^= hash << 25;
+	hash += hash >> 6;
+
+	return hash;
+}