From 353b31c7dae0cffb0d3bf82c2e4b5e715da33b83 Mon Sep 17 00:00:00 2001
From: Samuel Susla <samuelsusla@meta.com>
Date: Fri, 22 Sep 2023 05:53:13 -0700
Subject: [PATCH] introduce fnv1a hashing function (#39515)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/39515

changelog: [internal]

Implements FNV hashing algorithm: http://www.isthe.com/chongo/tech/comp/fnv/

Reviewed By: javache

Differential Revision: D49358327

fbshipit-source-id: b211da89ca7b6bea6ed1b0732e639bbc2de210f7
---
 .../react/renderer/core/PropsMacros.h         |  3 +-
 .../ReactCommon/react/utils/fnv1a.h           | 36 +++++++++++++++++++
 .../react/utils/tests/fnv1aTests.cpp          | 24 +++++++++++++
 3 files changed, 62 insertions(+), 1 deletion(-)
 create mode 100644 packages/react-native/ReactCommon/react/utils/fnv1a.h
 create mode 100644 packages/react-native/ReactCommon/react/utils/tests/fnv1aTests.cpp

diff --git a/packages/react-native/ReactCommon/react/renderer/core/PropsMacros.h b/packages/react-native/ReactCommon/react/renderer/core/PropsMacros.h
index d940fd6069c..3d2e5b221d9 100644
--- a/packages/react-native/ReactCommon/react/renderer/core/PropsMacros.h
+++ b/packages/react-native/ReactCommon/react/renderer/core/PropsMacros.h
@@ -8,6 +8,7 @@
 #pragma once
 
 #include <react/renderer/core/RawPropsPrimitives.h>
+#include <react/utils/fnv1a.h>
 #include <functional>
 
 // We need to use clang pragmas inside of a macro below,
@@ -23,7 +24,7 @@
   ([]() constexpr->RawPropsPropNameHash {                 \
     CLANG_PRAGMA("clang diagnostic push")                 \
     CLANG_PRAGMA("clang diagnostic ignored \"-Wshadow\"") \
-    return folly::hash::fnv32_buf(s, sizeof(s) - 1);      \
+    return facebook::react::fnv1a(s);                     \
     CLANG_PRAGMA("clang diagnostic pop")                  \
   }())
 
diff --git a/packages/react-native/ReactCommon/react/utils/fnv1a.h b/packages/react-native/ReactCommon/react/utils/fnv1a.h
new file mode 100644
index 00000000000..fe2721d4bc0
--- /dev/null
+++ b/packages/react-native/ReactCommon/react/utils/fnv1a.h
@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+namespace facebook::react {
+
+/**
+ * FNV-1a hash function implementation.
+ * Implemented as described in http://www.isthe.com/chongo/tech/comp/fnv/.
+ *
+ * Please use std::hash if possible. `fnv1a` should only be used in cases
+ * when std::hash does not provide the needed functionality. For example,
+ * constexpr.
+ */
+constexpr uint32_t fnv1a(std::string_view string) noexcept {
+  constexpr uint32_t offset_basis = 2166136261;
+
+  uint32_t hash = offset_basis;
+
+  for (auto const& c : string) {
+    hash ^= static_cast<int8_t>(c);
+    // Using shifts and adds instead of multiplication with a prime number.
+    // This is faster when compiled with optimizations.
+    hash +=
+        (hash << 1) + (hash << 4) + (hash << 7) + (hash << 8) + (hash << 24);
+  }
+
+  return hash;
+}
+
+} // namespace facebook::react
diff --git a/packages/react-native/ReactCommon/react/utils/tests/fnv1aTests.cpp b/packages/react-native/ReactCommon/react/utils/tests/fnv1aTests.cpp
new file mode 100644
index 00000000000..5c7b76d099a
--- /dev/null
+++ b/packages/react-native/ReactCommon/react/utils/tests/fnv1aTests.cpp
@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <gtest/gtest.h>
+#include <react/utils/fnv1a.h>
+
+namespace facebook::react {
+
+TEST(fnv1aTests, testBasicHashing) {
+  EXPECT_EQ(fnv1a("react"), fnv1a("react"));
+
+  EXPECT_NE(fnv1a("react"), fnv1a("tceat"));
+
+  auto string1 = "case 1";
+  auto string2 = "different string";
+  EXPECT_EQ(fnv1a(string1), fnv1a(string1));
+  EXPECT_NE(fnv1a(string1), fnv1a(string2));
+}
+
+} // namespace facebook::react