Make display unique id stable across x86 and x86_64 builds
... by using a minimal version of CityHash64 for the hash function.
std::hash differs between x86 and x86_64 and also:
"Hash functions are only required to produce the same result for the
same input within a single execution of a program;"
This is problematic for input device configuration files which
reference the display unique id.
Bug: b/186150820
Test: libsurfaceflinger_unittest
Change-Id: If15b66775fa48f14cc56bbd23536b61844b7ae37
diff --git a/services/surfaceflinger/DisplayHardware/Hash.h b/services/surfaceflinger/DisplayHardware/Hash.h
new file mode 100644
index 0000000..a7b6c71
--- /dev/null
+++ b/services/surfaceflinger/DisplayHardware/Hash.h
@@ -0,0 +1,27 @@
+/*
+ * Copyright 2021 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 <cstdint>
+#include <string_view>
+
+namespace android {
+
+// CityHash64 implementation that only hashes at most the first 16 characters of the given string.
+uint64_t cityHash64Len0To16(std::string_view sv);
+
+} // namespace android
\ No newline at end of file