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+// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
+// This source code is licensed under both the GPLv2 (found in the
+// COPYING file in the root directory) and Apache 2.0 License
+// (found in the LICENSE.Apache file in the root directory).
+//
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+#include "util/hash.h"
+
+#include <string>
+
+#include "port/lang.h"
+#include "util/coding.h"
+#include "util/hash128.h"
+#include "util/math128.h"
+#include "util/xxhash.h"
+#include "util/xxph3.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+uint64_t (*kGetSliceNPHash64UnseededFnPtr)(const Slice&) = &GetSliceHash64;
+
+uint32_t Hash(const char* data, size_t n, uint32_t seed) {
+ // MurmurHash1 - fast but mediocre quality
+ // https://github.com/aappleby/smhasher/wiki/MurmurHash1
+ //
+ const uint32_t m = 0xc6a4a793;
+ const uint32_t r = 24;
+ const char* limit = data + n;
+ uint32_t h = static_cast<uint32_t>(seed ^ (n * m));
+
+ // Pick up four bytes at a time
+ while (data + 4 <= limit) {
+ uint32_t w = DecodeFixed32(data);
+ data += 4;
+ h += w;
+ h *= m;
+ h ^= (h >> 16);
+ }
+
+ // Pick up remaining bytes
+ switch (limit - data) {
+ // Note: The original hash implementation used data[i] << shift, which
+ // promotes the char to int and then performs the shift. If the char is
+ // negative, the shift is undefined behavior in C++. The hash algorithm is
+ // part of the format definition, so we cannot change it; to obtain the same
+ // behavior in a legal way we just cast to uint32_t, which will do
+ // sign-extension. To guarantee compatibility with architectures where chars
+ // are unsigned we first cast the char to int8_t.
+ case 3:
+ h += static_cast<uint32_t>(static_cast<int8_t>(data[2])) << 16;
+ FALLTHROUGH_INTENDED;
+ case 2:
+ h += static_cast<uint32_t>(static_cast<int8_t>(data[1])) << 8;
+ FALLTHROUGH_INTENDED;
+ case 1:
+ h += static_cast<uint32_t>(static_cast<int8_t>(data[0]));
+ h *= m;
+ h ^= (h >> r);
+ break;
+ }
+ return h;
+}
+
+// We are standardizing on a preview release of XXH3, because that's
+// the best available at time of standardizing.
+//
+// In testing (mostly Intel Skylake), this hash function is much more
+// thorough than Hash32 and is almost universally faster. Hash() only
+// seems faster when passing runtime-sized keys of the same small size
+// (less than about 24 bytes) thousands of times in a row; this seems
+// to allow the branch predictor to work some magic. XXH3's speed is
+// much less dependent on branch prediction.
+//
+// Hashing with a prefix extractor is potentially a common case of
+// hashing objects of small, predictable size. We could consider
+// bundling hash functions specialized for particular lengths with
+// the prefix extractors.
+uint64_t Hash64(const char* data, size_t n, uint64_t seed) {
+ return XXPH3_64bits_withSeed(data, n, seed);
+}
+
+uint64_t Hash64(const char* data, size_t n) {
+ // Same as seed = 0
+ return XXPH3_64bits(data, n);
+}
+
+uint64_t GetSlicePartsNPHash64(const SliceParts& data, uint64_t seed) {
+ // TODO(ajkr): use XXH3 streaming APIs to avoid the copy/allocation.
+ size_t concat_len = 0;
+ for (int i = 0; i < data.num_parts; ++i) {
+ concat_len += data.parts[i].size();
+ }
+ std::string concat_data;
+ concat_data.reserve(concat_len);
+ for (int i = 0; i < data.num_parts; ++i) {
+ concat_data.append(data.parts[i].data(), data.parts[i].size());
+ }
+ assert(concat_data.size() == concat_len);
+ return NPHash64(concat_data.data(), concat_len, seed);
+}
+
+Unsigned128 Hash128(const char* data, size_t n, uint64_t seed) {
+ auto h = XXH3_128bits_withSeed(data, n, seed);
+ return (Unsigned128{h.high64} << 64) | (h.low64);
+}
+
+Unsigned128 Hash128(const char* data, size_t n) {
+ // Same as seed = 0
+ auto h = XXH3_128bits(data, n);
+ return (Unsigned128{h.high64} << 64) | (h.low64);
+}
+
+void Hash2x64(const char* data, size_t n, uint64_t* high64, uint64_t* low64) {
+ // Same as seed = 0
+ auto h = XXH3_128bits(data, n);
+ *high64 = h.high64;
+ *low64 = h.low64;
+}
+
+void Hash2x64(const char* data, size_t n, uint64_t seed, uint64_t* high64,
+ uint64_t* low64) {
+ auto h = XXH3_128bits_withSeed(data, n, seed);
+ *high64 = h.high64;
+ *low64 = h.low64;
+}
+
+namespace {
+
+inline uint64_t XXH3_avalanche(uint64_t h64) {
+ h64 ^= h64 >> 37;
+ h64 *= 0x165667919E3779F9U;
+ h64 ^= h64 >> 32;
+ return h64;
+}
+
+inline uint64_t XXH3_unavalanche(uint64_t h64) {
+ h64 ^= h64 >> 32;
+ h64 *= 0x8da8ee41d6df849U; // inverse of 0x165667919E3779F9U
+ h64 ^= h64 >> 37;
+ return h64;
+}
+
+} // namespace
+
+void BijectiveHash2x64(uint64_t in_high64, uint64_t in_low64, uint64_t seed,
+ uint64_t* out_high64, uint64_t* out_low64) {
+ // Adapted from XXH3_len_9to16_128b
+ const uint64_t bitflipl = /*secret part*/ 0x59973f0033362349U - seed;
+ const uint64_t bitfliph = /*secret part*/ 0xc202797692d63d58U + seed;
+ Unsigned128 tmp128 =
+ Multiply64to128(in_low64 ^ in_high64 ^ bitflipl, 0x9E3779B185EBCA87U);
+ uint64_t lo = Lower64of128(tmp128);
+ uint64_t hi = Upper64of128(tmp128);
+ lo += 0x3c0000000000000U; // (len - 1) << 54
+ in_high64 ^= bitfliph;
+ hi += in_high64 + (Lower32of64(in_high64) * uint64_t{0x85EBCA76});
+ lo ^= EndianSwapValue(hi);
+ tmp128 = Multiply64to128(lo, 0xC2B2AE3D27D4EB4FU);
+ lo = Lower64of128(tmp128);
+ hi = Upper64of128(tmp128) + (hi * 0xC2B2AE3D27D4EB4FU);
+ *out_low64 = XXH3_avalanche(lo);
+ *out_high64 = XXH3_avalanche(hi);
+}
+
+void BijectiveUnhash2x64(uint64_t in_high64, uint64_t in_low64, uint64_t seed,
+ uint64_t* out_high64, uint64_t* out_low64) {
+ // Inverted above (also consulting XXH3_len_9to16_128b)
+ const uint64_t bitflipl = /*secret part*/ 0x59973f0033362349U - seed;
+ const uint64_t bitfliph = /*secret part*/ 0xc202797692d63d58U + seed;
+ uint64_t lo = XXH3_unavalanche(in_low64);
+ uint64_t hi = XXH3_unavalanche(in_high64);
+ lo *= 0xba79078168d4baf; // inverse of 0xC2B2AE3D27D4EB4FU
+ hi -= Upper64of128(Multiply64to128(lo, 0xC2B2AE3D27D4EB4FU));
+ hi *= 0xba79078168d4baf; // inverse of 0xC2B2AE3D27D4EB4FU
+ lo ^= EndianSwapValue(hi);
+ lo -= 0x3c0000000000000U;
+ lo *= 0x887493432badb37U; // inverse of 0x9E3779B185EBCA87U
+ hi -= Upper64of128(Multiply64to128(lo, 0x9E3779B185EBCA87U));
+ uint32_t tmp32 = Lower32of64(hi) * 0xb6c92f47; // inverse of 0x85EBCA77
+ hi -= tmp32;
+ hi = (hi & 0xFFFFFFFF00000000U) -
+ ((tmp32 * uint64_t{0x85EBCA76}) & 0xFFFFFFFF00000000U) + tmp32;
+ hi ^= bitfliph;
+ lo ^= hi ^ bitflipl;
+ *out_high64 = hi;
+ *out_low64 = lo;
+}
+
+void BijectiveHash2x64(uint64_t in_high64, uint64_t in_low64,
+ uint64_t* out_high64, uint64_t* out_low64) {
+ BijectiveHash2x64(in_high64, in_low64, /*seed*/ 0, out_high64, out_low64);
+}
+
+void BijectiveUnhash2x64(uint64_t in_high64, uint64_t in_low64,
+ uint64_t* out_high64, uint64_t* out_low64) {
+ BijectiveUnhash2x64(in_high64, in_low64, /*seed*/ 0, out_high64, out_low64);
+}
+} // namespace ROCKSDB_NAMESPACE