commit 4afe85760a0c49461122b4c00ca8140df66e7609
author Jason Macnak <natsu@google.com> Fri Jul 16 13:57:41 2021 -0700
committer Jason Macnak <natsu@google.com> Wed Jul 21 10:43:43 2021 -0700
tree 8345d698853688198ca0a5264f2d5526679ef736
parent 620fd684f5ee3329a31d801f096eab6f9d14d2d5

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

services/surfaceflinger/tests/unittests/DisplayIdentificationTest.cpp

diff --git a/services/surfaceflinger/tests/unittests/DisplayIdentificationTest.cpp b/services/surfaceflinger/tests/unittests/DisplayIdentificationTest.cpp
index dc04b6d..cd4a5c9 100644
--- a/services/surfaceflinger/tests/unittests/DisplayIdentificationTest.cpp
+++ b/services/surfaceflinger/tests/unittests/DisplayIdentificationTest.cpp
@@ -25,6 +25,7 @@
 #include <gtest/gtest.h>
 
 #include "DisplayHardware/DisplayIdentification.h"
+#include "DisplayHardware/Hash.h"
 
 using ::testing::ElementsAre;
 
@@ -134,7 +135,7 @@
 }
 
 uint32_t hash(const char* str) {
-    return static_cast<uint32_t>(std::hash<std::string_view>()(str));
+    return static_cast<uint32_t>(cityHash64Len0To16(str));
 }
 
 } // namespace
@@ -309,9 +310,9 @@
     ASSERT_TRUE(tertiaryInfo);
 
     // Display IDs should be unique.
-    EXPECT_NE(primaryInfo->id, secondaryInfo->id);
-    EXPECT_NE(primaryInfo->id, tertiaryInfo->id);
-    EXPECT_NE(secondaryInfo->id, tertiaryInfo->id);
+    EXPECT_EQ(4633257497453176576, primaryInfo->id.value);
+    EXPECT_EQ(4621520285560261121, secondaryInfo->id.value);
+    EXPECT_EQ(4633127902230889474, tertiaryInfo->id.value);
 }
 
 TEST(DisplayIdentificationTest, deviceProductInfo) {