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9879b94f43
Murmurhash is generally superior to the Jenkins lookup3 hash according to the available figures. Perhaps we should generally replace our current hashes by murmurhash. For now, I'm introducing a parallel implementation to allow it to be used in cases where an incremental one-word-at-a-time hash is desirable. The first user will be added in an upcoming commit. Signed-off-by: Ben Pfaff <blp@nicira.com> Acked-by: Ethan Jackson <ethan@nicira.com>
120 lines
2.7 KiB
C
120 lines
2.7 KiB
C
/*
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* Copyright (c) 2008, 2009, 2010, 2012 Nicira, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <config.h>
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#include "hash.h"
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#include <string.h>
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#include "unaligned.h"
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/* Returns the hash of the 'n' 32-bit words at 'p', starting from 'basis'.
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* 'p' must be properly aligned. */
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uint32_t
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hash_words(const uint32_t *p, size_t n, uint32_t basis)
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{
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uint32_t a, b, c;
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a = b = c = 0xdeadbeef + (((uint32_t) n) << 2) + basis;
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while (n > 3) {
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a += p[0];
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b += p[1];
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c += p[2];
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hash_mix(&a, &b, &c);
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n -= 3;
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p += 3;
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}
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switch (n) {
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case 3:
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c += p[2];
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/* fall through */
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case 2:
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b += p[1];
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/* fall through */
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case 1:
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a += p[0];
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hash_final(&a, &b, &c);
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/* fall through */
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case 0:
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break;
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}
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return c;
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}
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/* Returns the hash of 'a', 'b', and 'c'. */
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uint32_t
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hash_3words(uint32_t a, uint32_t b, uint32_t c)
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{
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a += 0xdeadbeef;
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b += 0xdeadbeef;
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c += 0xdeadbeef;
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hash_final(&a, &b, &c);
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return c;
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}
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/* Returns the hash of 'a' and 'b'. */
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uint32_t
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hash_2words(uint32_t a, uint32_t b)
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{
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return hash_3words(a, b, 0);
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}
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/* Returns the hash of the 'n' bytes at 'p', starting from 'basis'. */
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uint32_t
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hash_bytes(const void *p_, size_t n, uint32_t basis)
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{
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const uint8_t *p = p_;
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uint32_t a, b, c;
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a = b = c = 0xdeadbeef + n + basis;
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while (n >= 12) {
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a += get_unaligned_u32((uint32_t *) p);
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b += get_unaligned_u32((uint32_t *) (p + 4));
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c += get_unaligned_u32((uint32_t *) (p + 8));
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hash_mix(&a, &b, &c);
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n -= 12;
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p += 12;
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}
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if (n) {
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uint32_t tmp[3];
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tmp[0] = tmp[1] = tmp[2] = 0;
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memcpy(tmp, p, n);
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a += tmp[0];
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b += tmp[1];
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c += tmp[2];
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hash_final(&a, &b, &c);
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}
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return c;
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}
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/* Returns the hash of the 'n' 32-bit words at 'p', starting from 'basis'.
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* 'p' must be properly aligned. */
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uint32_t
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mhash_words(const uint32_t p[], size_t n_words, uint32_t basis)
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{
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uint32_t hash;
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size_t i;
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hash = basis;
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for (i = 0; i < n_words; i++) {
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hash = mhash_add(hash, p[i]);
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}
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return mhash_finish(hash, n_words);
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}
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