FTL: Support ftl::stable_hash based on CityHash64
Extends stable hash from libui by increasing maximum string length
supported from 16 to 64 bytes (CityHash64 v1.0.1 - please see
http://code.google.com/p/cityhash/).
Bug: 185536303
Bug: 194863377
Test: ftl_test
Test: Compare with 64-bit std::hash<std::string_view>
Change-Id: Ib123d0690a0d2150aa51c91526784dcf77a65d46
diff --git a/include/ftl/hash.h b/include/ftl/hash.h
new file mode 100644
index 0000000..29a6f71
--- /dev/null
+++ b/include/ftl/hash.h
@@ -0,0 +1,44 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * 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
+ *
+ * http://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.
+ */
+
+#pragma once
+
+#include <cinttypes>
+#include <optional>
+#include <string_view>
+
+#include <ftl/details/hash.h>
+
+namespace android::ftl {
+
+// Non-cryptographic hash function (namely CityHash64) for strings with at most 64 characters.
+// Unlike std::hash, which returns std::size_t and is only required to produce the same result
+// for the same input within a single execution of a program, this hash is stable.
+inline std::optional<std::uint64_t> stable_hash(std::string_view view) {
+ const auto length = view.length();
+ if (length <= 16) {
+ return details::hash_length_0_to_16(view.data(), length);
+ }
+ if (length <= 32) {
+ return details::hash_length_17_to_32(view.data(), length);
+ }
+ if (length <= 64) {
+ return details::hash_length_33_to_64(view.data(), length);
+ }
+ return {};
+}
+
+} // namespace android::ftl