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samples/bpf: add Paul Hsieh's (LGPL 2.1) hash function SuperFastHash

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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>
This commit is contained in:
Jesper Dangaard Brouer 2018-08-10 14:02:57 +02:00 committed by Daniel Borkmann
parent eb91e4d4db
commit 1139568658
1 changed files with 55 additions and 0 deletions
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samples/bpf/hash_func01.h Normal file
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/* 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;
}