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.cpp b/services/surfaceflinger/DisplayHardware/Hash.cpp
new file mode 100644
index 0000000..6056c8d
--- /dev/null
+++ b/services/surfaceflinger/DisplayHardware/Hash.cpp
@@ -0,0 +1,93 @@
+/*
+ * 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.
+ */
+
+#undef LOG_TAG
+#define LOG_TAG "DisplayIdentification"
+
+#include <cstring>
+#include <type_traits>
+
+#include <log/log.h>
+
+#include "Hash.h"
+
+namespace android {
+namespace {
+
+template <class T>
+inline T load(const void* p) {
+ static_assert(std::is_integral<T>::value, "T must be integral");
+
+ T r;
+ std::memcpy(&r, p, sizeof(r));
+ return r;
+}
+
+uint64_t rotateByAtLeast1(uint64_t val, uint8_t shift) {
+ return (val >> shift) | (val << (64 - shift));
+}
+
+uint64_t shiftMix(uint64_t val) {
+ return val ^ (val >> 47);
+}
+
+uint64_t hash64Len16(uint64_t u, uint64_t v) {
+ constexpr uint64_t kMul = 0x9ddfea08eb382d69;
+ uint64_t a = (u ^ v) * kMul;
+ a ^= (a >> 47);
+ uint64_t b = (v ^ a) * kMul;
+ b ^= (b >> 47);
+ b *= kMul;
+ return b;
+}
+
+uint64_t hash64Len0To16(const char* s, uint64_t len) {
+ constexpr uint64_t k2 = 0x9ae16a3b2f90404f;
+ constexpr uint64_t k3 = 0xc949d7c7509e6557;
+
+ if (len > 8) {
+ const uint64_t a = load<uint64_t>(s);
+ const uint64_t b = load<uint64_t>(s + len - 8);
+ return hash64Len16(a, rotateByAtLeast1(b + len, static_cast<uint8_t>(len))) ^ b;
+ }
+ if (len >= 4) {
+ const uint32_t a = load<uint32_t>(s);
+ const uint32_t b = load<uint32_t>(s + len - 4);
+ return hash64Len16(len + (a << 3), b);
+ }
+ if (len > 0) {
+ const unsigned char a = static_cast<unsigned char>(s[0]);
+ const unsigned char b = static_cast<unsigned char>(s[len >> 1]);
+ const unsigned char c = static_cast<unsigned char>(s[len - 1]);
+ const uint32_t y = static_cast<uint32_t>(a) + (static_cast<uint32_t>(b) << 8);
+ const uint32_t z = static_cast<uint32_t>(len) + (static_cast<uint32_t>(c) << 2);
+ return shiftMix(y * k2 ^ z * k3) * k2;
+ }
+ return k2;
+}
+
+} // namespace
+
+uint64_t cityHash64Len0To16(std::string_view sv) {
+ auto len = sv.length();
+ if (len > 16) {
+ ALOGE("%s called with length %zu. Only hashing the first 16 chars", __FUNCTION__, len);
+ len = 16;
+ }
+ return hash64Len0To16(sv.data(), len);
+}
+
+} // namespace android
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