/* * virhashcode.c: hash code generation * * Copyright (C) 2012 Red Hat, Inc. * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library. If not, see * . * * The hash code generation is based on the public domain MurmurHash3 from Austin Appleby: * http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp * * We use only the 32 bit variant because the 2 produce different results while * we need to produce the same result regardless of the architecture as * clients can be both 64 or 32 bit at the same time. */ #include #include "virhashcode.h" static uint32_t rotl32(uint32_t x, int8_t r) { return (x << r) | (x >> (32 - r)); } /* slower than original but handles platforms that do only aligned reads */ static inline uint32_t getblock(const uint8_t *p, int i) { uint32_t r; size_t size = sizeof(r); memcpy(&r, &p[i * size], size); return r; } /* * Finalization mix - force all bits of a hash block to avalanche */ static inline uint32_t fmix(uint32_t h) { h ^= h >> 16; h *= 0x85ebca6b; h ^= h >> 13; h *= 0xc2b2ae35; h ^= h >> 16; return h; } uint32_t virHashCodeGen(const void *key, size_t len, uint32_t seed) { const uint8_t *blocks; const uint8_t *tail; size_t nblocks; uint32_t h1; uint32_t k1; uint32_t c1; uint32_t c2; size_t i; blocks = (const uint8_t *)key; nblocks = len / 4; h1 = seed; c1 = 0xcc9e2d51; c2 = 0x1b873593; /* body */ for (i = 0; i < nblocks; i++) { k1 = getblock(blocks, i); k1 *= c1; k1 = rotl32(k1, 15); k1 *= c2; h1 ^= k1; h1 = rotl32(h1, 13); h1 = h1 * 5 + 0xe6546b64; } /* tail */ tail = (const uint8_t *)key + nblocks * 4; k1 = 0; switch (len & 3) { case 3: k1 ^= tail[2] << 16; ATTRIBUTE_FALLTHROUGH; case 2: k1 ^= tail[1] << 8; ATTRIBUTE_FALLTHROUGH; case 1: k1 ^= tail[0]; k1 *= c1; k1 = rotl32(k1, 15); k1 *= c2; h1 ^= k1; ATTRIBUTE_FALLTHROUGH; default: break; } /* finalization */ h1 ^= len; h1 = fmix(h1); return h1; }