From 635aebeb6646d5845ba24b1aa27d58762dfecebb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Bylica?= <chfast@gmail.com>
Date: Mon, 22 Jul 2019 13:40:14 +0200
Subject: [PATCH] cpp: Add std::hash specializations for basic types

---
 include/evmc/evmc.hpp       | 49 +++++++++++++++++++++++++++++++++++++
 test/unittests/test_cpp.cpp | 26 ++++++++++++++++++++
 2 files changed, 75 insertions(+)

diff --git a/include/evmc/evmc.hpp b/include/evmc/evmc.hpp
index 9975ecd..e38cc20 100644
--- a/include/evmc/evmc.hpp
+++ b/include/evmc/evmc.hpp
@@ -7,6 +7,7 @@
 #include <evmc/evmc.h>
 #include <evmc/helpers.h>
 
+#include <functional>
 #include <initializer_list>
 #include <utility>
 
@@ -52,6 +53,18 @@ constexpr inline uint32_t load32be(const uint8_t* bytes) noexcept
            uint32_t{bytes[3]};
 }
 
+namespace fnv
+{
+constexpr auto prime = 0x100000001b3;              ///< The 64-bit FNV prime number.
+constexpr auto offset_basis = 0xcbf29ce484222325;  ///< The 64-bit FNV offset basis.
+
+/// The hashing transformation for 64-bit inputs based on the FNV-1a formula.
+constexpr inline uint64_t fnv1a_by64(uint64_t h, uint64_t x) noexcept
+{
+    return (h ^ x) * prime;
+}
+}  // namespace fnv
+
 
 /// The "equal" comparison operator for the evmc::address type.
 constexpr bool operator==(const address& a, const address& b) noexcept
@@ -479,3 +492,39 @@ constexpr evmc_host_interface interface{
 inline Host::Host() noexcept : evmc_context{&internal::interface} {}
 
 }  // namespace evmc
+
+
+namespace std
+{
+/// Hash operator template specialization for evmc::address. Needed for unordered containers.
+template <>
+struct hash<evmc::address>
+{
+    /// Hash operator using FNV1a-based folding.
+    constexpr size_t operator()(const evmc::address& s) const noexcept
+    {
+        using namespace evmc;
+        using namespace fnv;
+        return static_cast<size_t>(fnv1a_by64(
+            fnv1a_by64(fnv1a_by64(fnv::offset_basis, load64be(&s.bytes[0])), load64be(&s.bytes[8])),
+            load32be(&s.bytes[16])));
+    }
+};
+
+/// Hash operator template specialization for evmc::bytes32. Needed for unordered containers.
+template <>
+struct hash<evmc::bytes32>
+{
+    /// Hash operator using FNV1a-based folding.
+    constexpr size_t operator()(const evmc::bytes32& s) const noexcept
+    {
+        using namespace evmc;
+        using namespace fnv;
+        return static_cast<size_t>(
+            fnv1a_by64(fnv1a_by64(fnv1a_by64(fnv1a_by64(fnv::offset_basis, load64be(&s.bytes[0])),
+                                             load64be(&s.bytes[8])),
+                                  load64be(&s.bytes[16])),
+                       load64be(&s.bytes[24])));
+    }
+};
+}  // namespace std
diff --git a/test/unittests/test_cpp.cpp b/test/unittests/test_cpp.cpp
index 469be2a..74c02dd 100644
--- a/test/unittests/test_cpp.cpp
+++ b/test/unittests/test_cpp.cpp
@@ -16,6 +16,7 @@
 
 #include <cstring>
 
+
 TEST(cpp, address)
 {
     evmc::address a;
@@ -46,6 +47,31 @@ TEST(cpp, bytes32)
     EXPECT_TRUE(std::equal(std::begin(b.bytes), std::end(b.bytes), std::begin(other.bytes)));
 }
 
+TEST(cpp, std_hash)
+{
+#pragma warning(push)
+#pragma warning(disable : 4307 /* integral constant overflow */)
+#pragma warning(disable : 4309 /* 'static_cast': truncation of constant value */)
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1910 /* Only for Visual Studio 2017+ */)
+    static_assert(std::hash<evmc::address>{}({}) == static_cast<size_t>(0xd94d12186c0f2fb7), "");
+    static_assert(std::hash<evmc::bytes32>{}({}) == static_cast<size_t>(0x4d25767f9dce13f5), "");
+#endif
+
+    EXPECT_EQ(std::hash<evmc::address>{}({}), static_cast<size_t>(0xd94d12186c0f2fb7));
+    EXPECT_EQ(std::hash<evmc::bytes32>{}({}), static_cast<size_t>(0x4d25767f9dce13f5));
+
+    auto ea = evmc::address{};
+    std::fill_n(ea.bytes, sizeof(ea), uint8_t{0xee});
+    EXPECT_EQ(std::hash<evmc::address>{}(ea), static_cast<size_t>(0x41dc0178e01b7cd9));
+
+    auto eb = evmc::bytes32{};
+    std::fill_n(eb.bytes, sizeof(eb), uint8_t{0xee});
+    EXPECT_EQ(std::hash<evmc::bytes32>{}(eb), static_cast<size_t>(0xbb14e5c56b477375));
+
+#pragma warning(pop)
+}
+
 TEST(cpp, address_comparison)
 {
     const auto zero = evmc::address{};