| // 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_ |
