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adf846d3c9
Use ATTRIBUTE_FALLTHROUGH, introduced by commit
5d84f5961b, instead of comments to
indicate that the fall through is an intentional behavior.
Signed-off-by: Marc Hartmayer <mhartmay@linux.vnet.ibm.com>
Reviewed-by: Boris Fiuczynski <fiuczy@linux.vnet.ibm.com>
Reviewed-by: Bjoern Walk <bwalk@linux.vnet.ibm.com>
122 lines
2.7 KiB
C
122 lines
2.7 KiB
C
/*
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* virhashcode.c: hash code generation
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*
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* Copyright (C) 2012 Red Hat, Inc.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library. If not, see
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* <http://www.gnu.org/licenses/>.
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*
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* The hash code generation is based on the public domain MurmurHash3 from Austin Appleby:
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* http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp
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*
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* We use only the 32 bit variant because the 2 produce different results while
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* we need to produce the same result regardless of the architecture as
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* clients can be both 64 or 32 bit at the same time.
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*/
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#include <config.h>
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#include "virhashcode.h"
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#include "bitrotate.h"
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/* slower than original but handles platforms that do only aligned reads */
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static inline uint32_t getblock(const uint8_t *p, int i)
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{
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uint32_t r;
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size_t size = sizeof(r);
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memcpy(&r, &p[i * size], size);
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return r;
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}
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/*
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* Finalization mix - force all bits of a hash block to avalanche
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*/
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static inline uint32_t fmix(uint32_t h)
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{
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h ^= h >> 16;
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h *= 0x85ebca6b;
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h ^= h >> 13;
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h *= 0xc2b2ae35;
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h ^= h >> 16;
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return h;
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}
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uint32_t virHashCodeGen(const void *key, size_t len, uint32_t seed)
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{
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const uint8_t *blocks;
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const uint8_t *tail;
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size_t nblocks;
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uint32_t h1;
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uint32_t k1;
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uint32_t c1;
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uint32_t c2;
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size_t i;
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blocks = (const uint8_t *)key;
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nblocks = len / 4;
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h1 = seed;
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c1 = 0xcc9e2d51;
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c2 = 0x1b873593;
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/* body */
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for (i = 0; i < nblocks; i++) {
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k1 = getblock(blocks, i);
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k1 *= c1;
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k1 = rotl32(k1, 15);
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k1 *= c2;
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h1 ^= k1;
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h1 = rotl32(h1, 13);
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h1 = h1 * 5 + 0xe6546b64;
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}
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/* tail */
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tail = (const uint8_t *)key + nblocks * 4;
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k1 = 0;
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switch (len & 3) {
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case 3:
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k1 ^= tail[2] << 16;
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ATTRIBUTE_FALLTHROUGH;
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case 2:
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k1 ^= tail[1] << 8;
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ATTRIBUTE_FALLTHROUGH;
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case 1:
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k1 ^= tail[0];
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k1 *= c1;
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k1 = rotl32(k1, 15);
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k1 *= c2;
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h1 ^= k1;
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ATTRIBUTE_FALLTHROUGH;
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default:
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break;
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}
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/* finalization */
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h1 ^= len;
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h1 = fmix(h1);
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return h1;
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}
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