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Diffstat (limited to 'third_party/abseil_cpp/absl/hash/internal/city.h')
-rw-r--r-- | third_party/abseil_cpp/absl/hash/internal/city.h | 78 |
1 files changed, 78 insertions, 0 deletions
diff --git a/third_party/abseil_cpp/absl/hash/internal/city.h b/third_party/abseil_cpp/absl/hash/internal/city.h new file mode 100644 index 000000000000..393da0b95d9f --- /dev/null +++ b/third_party/abseil_cpp/absl/hash/internal/city.h @@ -0,0 +1,78 @@ +// Copyright 2018 The Abseil Authors. +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// https://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. +// +// https://code.google.com/p/cityhash/ +// +// This file provides a few functions for hashing strings. All of them are +// high-quality functions in the sense that they pass standard tests such +// as Austin Appleby's SMHasher. They are also fast. +// +// For 64-bit x86 code, on short strings, we don't know of anything faster than +// CityHash64 that is of comparable quality. We believe our nearest competitor +// is Murmur3. For 64-bit x86 code, CityHash64 is an excellent choice for hash +// tables and most other hashing (excluding cryptography). +// +// For 32-bit x86 code, we don't know of anything faster than CityHash32 that +// is of comparable quality. We believe our nearest competitor is Murmur3A. +// (On 64-bit CPUs, it is typically faster to use the other CityHash variants.) +// +// Functions in the CityHash family are not suitable for cryptography. +// +// Please see CityHash's README file for more details on our performance +// measurements and so on. +// +// WARNING: This code has been only lightly tested on big-endian platforms! +// It is known to work well on little-endian platforms that have a small penalty +// for unaligned reads, such as current Intel and AMD moderate-to-high-end CPUs. +// It should work on all 32-bit and 64-bit platforms that allow unaligned reads; +// bug reports are welcome. +// +// By the way, for some hash functions, given strings a and b, the hash +// of a+b is easily derived from the hashes of a and b. This property +// doesn't hold for any hash functions in this file. + +#ifndef ABSL_HASH_INTERNAL_CITY_H_ +#define ABSL_HASH_INTERNAL_CITY_H_ + +#include <stdint.h> +#include <stdlib.h> // for size_t. + +#include <utility> + +#include "absl/base/config.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace hash_internal { + +// Hash function for a byte array. +uint64_t CityHash64(const char *s, size_t len); + +// Hash function for a byte array. For convenience, a 64-bit seed is also +// hashed into the result. +uint64_t CityHash64WithSeed(const char *s, size_t len, uint64_t seed); + +// Hash function for a byte array. For convenience, two seeds are also +// hashed into the result. +uint64_t CityHash64WithSeeds(const char *s, size_t len, uint64_t seed0, + uint64_t seed1); + +// Hash function for a byte array. Most useful in 32-bit binaries. +uint32_t CityHash32(const char *s, size_t len); + +} // namespace hash_internal +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_HASH_INTERNAL_CITY_H_ |