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src/hash.c
84 строки
1 KB
Romain Geissler
hash: fix strict aliasing UB in MurMur hash implementation
18 мар 2025, 03:28
18 мар 2025, 03:28
614530b
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/** * Seccomp Library hash code * */ /* * This code is based on MurmurHash3.cpp from Austin Appleby and is placed in * the public domain. * * https://github.com/aappleby/smhasher * */ #include <stdlib.h> #include <string.h> #include <inttypes.h> #include "hash.h" static inline uint32_t rotl32(uint32_t x, int8_t r) { return (x << r) | (x >> (32 - r)); } static inline uint32_t fmix32(uint32_t h) { h ^= h >> 16; h *= 0x85ebca6b; h ^= h >> 13; h *= 0xc2b2ae35; h ^= h >> 16; return h; } /* NOTE: this is an implementation of MurmurHash3_x86_32 */ uint32_t hash(const void *key, size_t length) { const uint8_t *data = (const uint8_t *)key; const uint8_t *tail; const int nblocks = length / 4; const uint32_t c1 = 0xcc9e2d51; const uint32_t c2 = 0x1b873593; uint32_t k1; uint32_t k2 = 0; int i; /* NOTE: we always force a seed of 0 */ uint32_t h1 = 0; /* body */ for(i = -nblocks; i; i++) { memcpy(&k1, data + (nblocks + i) * sizeof(uint32_t), sizeof(uint32_t)); k1 *= c1; k1 = rotl32(k1, 15); k1 *= c2; h1 ^= k1; h1 = rotl32(h1, 13); h1 = h1 * 5 + 0xe6546b64; } /* tail */ tail = data + nblocks * sizeof(uint32_t); switch(length & 3) { case 3: k2 ^= tail[2] << 16; case 2: k2 ^= tail[1] << 8; case 1: k2 ^= tail[0]; k2 *= c1; k2 = rotl32(k2, 15); k2 *= c2; h1 ^= k2; }; /* finalization */ h1 ^= length; h1 = fmix32(h1); return h1; }