mirror of https://gitee.com/bigwinds/arangodb
139 lines
3.8 KiB
C++
139 lines
3.8 KiB
C++
/* The MIT License
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Copyright (C) 2012 Zilong Tan (eric.zltan@gmail.com)
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Permission is hereby granted, free of charge, to any person
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obtaining a copy of this software and associated documentation
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files (the "Software"), to deal in the Software without
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restriction, including without limitation the rights to use, copy,
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modify, merge, publish, distribute, sublicense, and/or sell copies
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of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be
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included in all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.
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*/
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#include "fasthash.h"
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static constexpr uint64_t m = 0x880355f21e6d1965ULL;
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// Compression function for Merkle-Damgard construction.
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// This function is generated using the framework provided.
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static inline uint64_t mix(uint64_t h) {
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h ^= h >> 23;
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h *= 0x2127599bf4325c37ULL;
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h ^= h >> 47;
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return h;
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}
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uint64_t fasthash64_uint64(uint64_t value, uint64_t seed) {
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uint64_t h = seed ^ 4619197404915747624ULL; // this is h = seed ^ (sizeof(uint64_t) * m), but prevents VS warning C4307: integral constant overflow
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h ^= mix(value);
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h *= m;
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return mix(h);
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}
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uint64_t fasthash64(const void* buf, size_t len, uint64_t seed) {
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#ifndef TRI_UNALIGNED_ACCESS
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// byte-wise hashing to support platforms that don't permit
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// unaligned accesses of uint64_t values (which is the default
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// memory access strategy of fasthash64)
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uint8_t const* pos = (uint8_t const*)buf;
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uint8_t const* end = pos + len;
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uint64_t h = seed ^ (len * m);
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while (pos != end) {
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len = end - pos;
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if (len > 8) {
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len = 8;
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}
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uint64_t v = 0;
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switch (len) {
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case 8:
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v ^= (uint64_t)pos[7] << 56;
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case 7:
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v ^= (uint64_t)pos[6] << 48;
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case 6:
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v ^= (uint64_t)pos[5] << 40;
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case 5:
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v ^= (uint64_t)pos[4] << 32;
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case 4:
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v ^= (uint64_t)pos[3] << 24;
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case 3:
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v ^= (uint64_t)pos[2] << 16;
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case 2:
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v ^= (uint64_t)pos[1] << 8;
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case 1:
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v ^= (uint64_t)pos[0];
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h ^= mix(v);
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h *= m;
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}
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pos += len;
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}
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return mix(h);
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#else
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// uint64_t-wise hashing for platforms that allow dereferencing
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// unaligned pointers to uint64_t memory
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// this is the original version of fasthash64
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uint64_t const* pos = (uint64_t const*)buf;
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uint64_t const* end = pos + (len / 8);
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const unsigned char* pos2;
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uint64_t h = seed ^ (len * m);
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uint64_t v;
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while (pos != end) {
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v = *pos++;
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h ^= mix(v);
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h *= m;
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}
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pos2 = (const unsigned char*)pos;
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v = 0;
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switch (len & 7) {
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case 7:
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v ^= (uint64_t)pos2[6] << 48;
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case 6:
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v ^= (uint64_t)pos2[5] << 40;
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case 5:
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v ^= (uint64_t)pos2[4] << 32;
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case 4:
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v ^= (uint64_t)pos2[3] << 24;
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case 3:
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v ^= (uint64_t)pos2[2] << 16;
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case 2:
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v ^= (uint64_t)pos2[1] << 8;
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case 1:
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v ^= (uint64_t)pos2[0];
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h ^= mix(v);
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h *= m;
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}
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return mix(h);
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#endif
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}
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uint32_t fasthash32(const void* buf, size_t len, uint32_t seed) {
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// the following trick converts the 64-bit hashcode to Fermat
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// residue, which shall retain information from both the higher
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// and lower parts of hashcode.
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uint64_t h = fasthash64(buf, len, seed);
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return (uint32_t)(h - (h >> 32));
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}
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