1 /* 2 * Copyright 2024 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #pragma once 18 19 #include <cinttypes> 20 #include <optional> 21 #include <string_view> 22 23 #include <ftl/details/hash.h> 24 25 namespace android::ftl { 26 27 // Non-cryptographic hash function (namely CityHash64) for strings with at most 64 characters. 28 // Unlike std::hash, which returns std::size_t and is only required to produce the same result 29 // for the same input within a single execution of a program, this hash is stable. stable_hash(std::string_view view)30 inline std::optional<std::uint64_t> stable_hash(std::string_view view) { 31 const auto length = view.length(); 32 if (length <= 16) { 33 return details::hash_length_0_to_16(view.data(), length); 34 } 35 if (length <= 32) { 36 return details::hash_length_17_to_32(view.data(), length); 37 } 38 if (length <= 64) { 39 return details::hash_length_33_to_64(view.data(), length); 40 } 41 return {}; 42 } 43 44 } // namespace android::ftl 45