// 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.
//
-// Simple hash function used for internal data structures
+// Common hash functions with convenient interfaces. If hashing a
+// statically-sized input in a performance-critical context, consider
+// calling a specific hash implementation directly, such as
+// XXH3p_64bits from xxhash.h.
+//
+// Since this is a very common header, implementation details are kept
+// out-of-line. Out-of-lining also aids in tracking the time spent in
+// hashing functions. Inlining is of limited benefit for runtime-sized
+// hash inputs.
#pragma once
#include <stddef.h>
#include <stdint.h>
#include "rocksdb/slice.h"
-#include "util/murmurhash.h"
-namespace rocksdb {
+namespace ROCKSDB_NAMESPACE {
+
+// Stable/persistent 64-bit hash. Higher quality and generally faster than
+// Hash(), especially for inputs > 24 bytes.
+extern uint64_t Hash64(const char* data, size_t n, uint64_t seed);
-// Non-persistent hash. Only used for in-memory data structure
-// The hash results are applicable to change.
-extern uint64_t NPHash64(const char* data, size_t n, uint32_t seed);
+// Specific optimization without seed (same as seed = 0)
+extern uint64_t Hash64(const char* data, size_t n);
+
+// Non-persistent hash. Must only used for in-memory data structure.
+// The hash results are thus applicable to change. (Thus, it rarely makes
+// sense to specify a seed for this function.)
+inline uint64_t NPHash64(const char* data, size_t n, uint32_t seed) {
+ // Currently same as Hash64
+ return Hash64(data, n, seed);
+}
+
+// Specific optimization without seed (same as seed = 0)
+inline uint64_t NPHash64(const char* data, size_t n) {
+ // Currently same as Hash64
+ return Hash64(data, n);
+}
+// Stable/persistent 32-bit hash. Moderate quality and high speed on
+// small inputs.
+// TODO: consider rename to Hash32
extern uint32_t Hash(const char* data, size_t n, uint32_t seed);
+// TODO: consider rename to LegacyBloomHash32
inline uint32_t BloomHash(const Slice& key) {
return Hash(key.data(), key.size(), 0xbc9f1d34);
}
+inline uint64_t GetSliceHash64(const Slice& key) {
+ return Hash64(key.data(), key.size());
+}
+
inline uint64_t GetSliceNPHash64(const Slice& s) {
- return NPHash64(s.data(), s.size(), 0);
+ return NPHash64(s.data(), s.size());
}
+// TODO: consider rename to GetSliceHash32
inline uint32_t GetSliceHash(const Slice& s) {
return Hash(s.data(), s.size(), 397);
}
-inline uint64_t NPHash64(const char* data, size_t n, uint32_t seed) {
- // Right now murmurhash2B is used. It should able to be freely
- // changed to a better hash, without worrying about backward
- // compatibility issue.
- return MURMUR_HASH(data, static_cast<int>(n),
- static_cast<unsigned int>(seed));
+// Useful for splitting up a 64-bit hash
+inline uint32_t Upper32of64(uint64_t v) {
+ return static_cast<uint32_t>(v >> 32);
}
+inline uint32_t Lower32of64(uint64_t v) { return static_cast<uint32_t>(v); }
// std::hash compatible interface.
+// TODO: consider rename to SliceHasher32
struct SliceHasher {
uint32_t operator()(const Slice& s) const { return GetSliceHash(s); }
};
-} // namespace rocksdb
+// An alternative to % for mapping a hash value to an arbitrary range. See
+// https://github.com/lemire/fastrange
+inline uint32_t fastrange32(uint32_t hash, uint32_t range) {
+ uint64_t product = uint64_t{range} * hash;
+ return static_cast<uint32_t>(product >> 32);
+}
+
+// An alternative to % for mapping a 64-bit hash value to an arbitrary range
+// that fits in size_t. See https://github.com/lemire/fastrange
+// We find size_t more convenient than uint64_t for the range, with side
+// benefit of better optimization on 32-bit platforms.
+inline size_t fastrange64(uint64_t hash, size_t range) {
+#if defined(HAVE_UINT128_EXTENSION)
+ // Can use compiler's 128-bit type. Trust it to do the right thing.
+ __uint128_t wide = __uint128_t{range} * hash;
+ return static_cast<size_t>(wide >> 64);
+#else
+ // Fall back: full decomposition.
+ // NOTE: GCC seems to fully understand this code as 64-bit x {32 or 64}-bit
+ // -> {96 or 128}-bit multiplication and optimize it down to a single
+ // wide-result multiplication (64-bit platform) or two wide-result
+ // multiplications (32-bit platforms, where range64 >> 32 is zero).
+ uint64_t range64 = range; // ok to shift by 32, even if size_t is 32-bit
+ uint64_t tmp = uint64_t{range64 & 0xffffFFFF} * uint64_t{hash & 0xffffFFFF};
+ tmp >>= 32;
+ tmp += uint64_t{range64 & 0xffffFFFF} * uint64_t{hash >> 32};
+ // Avoid overflow: first add lower 32 of tmp2, and later upper 32
+ uint64_t tmp2 = uint64_t{range64 >> 32} * uint64_t{hash & 0xffffFFFF};
+ tmp += static_cast<uint32_t>(tmp2);
+ tmp >>= 32;
+ tmp += (tmp2 >> 32);
+ tmp += uint64_t{range64 >> 32} * uint64_t{hash >> 32};
+ return static_cast<size_t>(tmp);
+#endif
+}
+
+} // namespace ROCKSDB_NAMESPACE
projects / ceph.git / blobdiff