samples/bpf: 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>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/samples/bpf/hash_func01.h b/samples/bpf/hash_func01.h
new file mode 100644 (file)
index 0000000..3825581
--- /dev/null
+++ b/samples/bpf/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 __u16 *) (d)))
+
+static __always_inline
+__u32 SuperFastHash (const char *data, int len, __u32 initval) {
+       __u32 hash = initval;
+       __u32 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 (__u16);
+               hash  += hash >> 11;
+       }
+
+       /* Handle end cases */
+       switch (rem) {
+        case 3: hash += get16bits (data);
+                hash ^= hash << 16;
+                hash ^= ((signed char)data[sizeof (__u16)]) << 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;
+}