/* * Copyright (C) 2012, 2013, 2014 * Dale Weiler * * Permission is hereby granted, free of charge, to any person obtaining a copy of * this software and associated documentation files (the "Software"), to deal in * the Software without restriction, including without limitation the rights to * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies * of the Software, and to permit persons to whom the Software is furnished to do * so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in all * copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE * SOFTWARE. */ #include "gmqcc.h" #include #if defined(_MSC_VER) # define HASH_ROTL32(X, Y) _rotl((X), (Y)) #elif defined (__GNUC__) && (defined(__i386__) || defined(__amd64__)) static GMQCC_FORCEINLINE uint32_t hash_rotl32(volatile uint32_t x, int8_t r) { __asm__ __volatile__ ("roll %1,%0" : "+r"(x) : "c"(r)); return x; } # define HASH_ROTL32(X, Y) hash_rotl32((volatile uint32_t)(X), (Y)) #else # define HASH_ROTL32(X, Y) (((X) << (Y)) | ((X) >> (32 - (Y)))) #endif /* * This is a version of the Murmur3 hashing function optimized for various * compilers/architectures. It uses the traditional Murmur2 mix staging * but fixes the mix staging inner loops. * * Murmur 2 contains an inner loop such as: * while (l >= 4) { * u32 k = *(u32*)d; * k *= m; * k ^= k >> r; * k *= m; * * h *= m; * h ^= k; * d += 4; * l -= 4; * } * * The two u32s that form the key are the same value for x * this premix stage will perform the same results for both values. Unrolled * this produces just: * x *= m; * x ^= x >> r; * x *= m; * * h *= m; * h ^= x; * h *= m; * h ^= x; * * This appears to be fine, except what happens when m == 1? well x * cancels out entierly, leaving just: * x ^= x >> r; * h ^= x; * h ^= x; * * So all keys hash to the same value, but how often does m == 1? * well, it turns out testing x for all possible values yeilds only * 172,013,942 unique results instead of 2^32. So nearly ~4.6 bits * are cancelled out on average! * * This means we have a 14.5% higher chance of collision. This is where * Murmur3 comes in to save the day. */ static GMQCC_FORCEINLINE uint32_t hash_murmur_mix32(uint32_t hash) { hash ^= hash >> 16; hash *= 0x85EBCA6B; hash ^= hash >> 13; hash *= 0xC2B2AE35; hash ^= hash >> 16; return hash; } /* * These constants were calculated with SMHasher to determine the best * case senario for Murmur3: * http://code.google.com/p/smhasher/ */ #define HASH_MURMUR_MASK1 0xCC9E2D51 #define HASH_MURMUR_MASK2 0x1B873593 #define HASH_MURMUR_SEED 0x9747B28C #if PLATFORM_BYTE_ORDER == GMQCC_BYTE_ORDER_LITTLE # define HASH_MURMUR_SAFEREAD(PTR) (*((uint32_t*)(PTR))) #elif PLATFORM_BYTE_ORDER == GMQCC_BYTE_ORDER_BIG # if defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR >= 3)) # define HASH_MURMUR_SAFEREAD(PTR) (__builtin_bswap32(*((uint32_t*)(PTR)))) # endif #endif /* Process individual bytes at this point since the endianess isn't known. */ #ifndef HASH_MURMUR_SAFEREAD # define HASH_MURMUR_SAFEREAD(PTR) ((PTR)[0] | (PTR)[1] << 8 | (PTR)[2] << 16 | (PTR)[3] << 24) #endif #define HASH_MURMUR_BLOCK(H, K) \ do { \ K *= HASH_MURMUR_MASK1; \ K = HASH_ROTL32(K, 15); \ K *= HASH_MURMUR_MASK2; \ H ^= K; \ H = HASH_ROTL32(H, 13); \ H = H * 5 + 0xE6546B64; \ } while (0) #define HASH_MURMUR_BYTES(COUNT, H, C, N, PTR, LENGTH) \ do { \ int i = COUNT; \ while (i--) { \ C = C >> 8 | *PTR++ << 24; \ N++; \ LENGTH--; \ if (N == 4) { \ HASH_MURMUR_BLOCK(H, C); \ N = 0; \ } \ } \ } while (0) #define HASH_MURMUR_TAIL(P, Z, H, C, N, PTR, LEN) \ do { \ LEN -= LEN/4*4; \ HASH_MURMUR_BYTES(LEN, H, C, N, PTR, LEN); \ *P = H; \ *Z = ((C) & ~0xFF) | (N); \ } while (0) #if PLATFORM_BYTE_ORDER == GMQCC_BYTE_ORDER_LITTLE static GMQCC_FORCEINLINE void hash_murmur_process(uint32_t *ph1, uint32_t *carry, const void *key, int length) { uint32_t h1 = *ph1; uint32_t c = *carry; const uint8_t *ptr = (uint8_t*)key; const uint8_t *end; int n = c & 3; int it = (4 - n) & 3; if (it && it <= length) HASH_MURMUR_BYTES(it, h1, c, n, ptr, length); end = ptr + length/4*4; for (; ptr < end; ptr += 4) { uint32_t k1 = HASH_MURMUR_SAFEREAD(ptr); HASH_MURMUR_BLOCK(h1, k1); } HASH_MURMUR_TAIL(ph1, carry, h1, c, n, ptr, length); } #else static GMQCC_FORCEINLINE void hash_murmur_process(uint32_t *ph1, uint32_t *carry, const void *key, int length) { uint32_t k1; uint32_t h1 = *ph1; uint32_t c = *carry; const uint8_t *ptr = (uint8_t*)key; const uint8_t *end; int n = c & 3; int it = -(long)ptr & 3; if (it && it <= length) HASH_MURMUR_BYTES(it, h1, c, n, ptr, length); end = ptr + length / 4 * 4; switch (n) { case 0: for (; ptr < end; ptr += 4) { k1 = HASH_MURMUR_SAFEREAD(ptr); HASH_MURMUR_BLOCK(h1, k1); } break; # define NEXT(N, RIGHT, LEFT) \ case N: \ for (; ptr < end; ptr += 4) { \ k1 = c >> RIGHT; \ c = HASH_MURMUR_SAFEREAD(ptr); \ k1 |= c << LEFT; \ HASH_MURMUR_BLOCK(h1, k1); \ } \ break NEXT(1, 24, 8); NEXT(2, 16, 16); NEXT(3, 8, 24); #undef NEXT } HASH_MURMUR_TAIL(ph1, carry, h1, c, n, ptr, length); } #endif static GMQCC_FORCEINLINE uint32_t hash_murmur_result(uint32_t hash, uint32_t carry, size_t length) { uint32_t k1; int n = carry & 3; if (GMQCC_LIKELY(n)) { k1 = carry >> (4 - n) * 8; k1 *= HASH_MURMUR_MASK1; k1 = HASH_ROTL32(k1, 15); k1 *= HASH_MURMUR_MASK2; hash ^= k1; } hash ^= length; hash = hash_murmur_mix32(hash); return hash; } static GMQCC_FORCEINLINE uint32_t hash_murmur(const void *GMQCC_RESTRICT key, size_t length) { uint32_t hash = HASH_MURMUR_SEED; uint32_t carry = 0; hash_murmur_process(&hash, &carry, key, length); return hash_murmur_result(hash, carry, length); } size_t hash(const char *key) { const char *s = key; const char *a = s; const size_t *w; for (; (uintptr_t)s % sizeof(size_t); s++) if (!*s) return hash_murmur((const void *)key, s-a); for (w = (const size_t*)s; !((*w-(size_t)-1/UCHAR_MAX) & ~*w & ((size_t)-1/UCHAR_MAX) * (UCHAR_MAX / 2 + 1)); w++); for (s = (const char *)w; *s; s++); return hash_murmur((const void *)key, s-a); } #undef HASH_ROTL32 #undef HASH_MURMUR_MASK1 #undef HASH_MURMUR_MASK2 #undef HASH_MURMUR_SEED #undef HASH_MURMUR_SAFEREAD #undef HASH_MURMUR_BLOCK #undef HASH_MURMUR_BYTES #undef HASH_MURMUR_TAIL