From cbca4be23757dfbdb54aa7177a1bce04f12364eb Mon Sep 17 00:00:00 2001
From: Kurt Sassenrath <kurt@sassenrath.me>
Date: Mon, 6 Nov 2023 22:56:35 -0800
Subject: [PATCH] Add hash test

---
 include/parselink/proto/session_id.h | 25 +++++++++++++++++++++----
 tests/proto/test_session_id.cpp      | 18 +++++++++++++-----
 2 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/include/parselink/proto/session_id.h b/include/parselink/proto/session_id.h
index 45ee1d0..0ef8f30 100644
--- a/include/parselink/proto/session_id.h
+++ b/include/parselink/proto/session_id.h
@@ -21,6 +21,8 @@
 
 #include <array>
 #include <cstddef>
+#include <cstdint>
+#include <functional>
 #include <span>
 
 namespace parselink {
@@ -55,12 +57,12 @@ public:
 
     [[nodiscard]] constexpr auto operator==(
             std::span<std::byte const> other) const noexcept {
-        return std::equal(bytes_.begin(), bytes_.end(), other.begin(), other.end());
+        return std::equal(
+                bytes_.begin(), bytes_.end(), other.begin(), other.end());
     }
 
-    constexpr std::span<std::byte const> raw() const noexcept {
-        return bytes_;
-    }
+    constexpr std::span<std::byte const> raw() const noexcept { return bytes_; }
+
 private:
     std::array<std::byte, 32> bytes_;
 };
@@ -68,4 +70,19 @@ private:
 } // namespace proto
 } // namespace parselink
 
+// Hashing support
+template <>
+struct std::hash<parselink::proto::session_id> {
+    constexpr static std::uint32_t seed_var = 0x811c9dc5;
+    constexpr static std::uint32_t factor = 0x01000193;
+
+    constexpr auto operator()(auto const& sid) const noexcept {
+        std::uint32_t digest = seed_var * factor;
+        for (auto byte : sid.raw()) {
+            digest = (digest ^ static_cast<std::uint32_t>(byte)) * factor;
+        }
+        return digest >> 8;
+    }
+};
+
 #endif // session_id_6598f9bae1cbb501
diff --git a/tests/proto/test_session_id.cpp b/tests/proto/test_session_id.cpp
index a1122f8..c2209a1 100644
--- a/tests/proto/test_session_id.cpp
+++ b/tests/proto/test_session_id.cpp
@@ -1,8 +1,9 @@
 #include <boost/ut.hpp>
 #include <parselink/proto/session_id.h>
-
 #include <set>
 
+#include <fmt/format.h>
+
 namespace {
 
 using namespace boost::ut;
@@ -14,8 +15,9 @@ constexpr std::array<std::byte, sizeof...(Bytes)> make_bytes(Bytes&&... bytes) {
 }
 
 constexpr std::array<std::byte, 32> null_id_bytes = {};
+constexpr std::size_t expected_null_hash = 0xd98558;
 
-}
+} // namespace
 
 suite session_id_tests = [] {
     "test explicitly generated session ids"_test = [] {
@@ -23,15 +25,21 @@ suite session_id_tests = [] {
         constexpr session_id sid2(null_id_bytes);
         expect(sid1 == sid2);
         expect(sid1 == null_id_bytes);
-        constexpr auto basic_id = make_bytes(
-                0x0, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
-                0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f);
+        constexpr auto basic_id = make_bytes(0x0, 0x01, 0x02, 0x03, 0x04, 0x05,
+                0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
+                0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19,
+                0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f);
         constexpr session_id sid3(basic_id);
         constexpr session_id sid4(basic_id);
         expect(sid3 == sid4);
         expect(sid3 == basic_id);
     };
 
+    "test hashing"_test = [] {
+        session_id sid(null_id_bytes);
+        expect(std::hash<decltype(sid)>{}(sid) == expected_null_hash);
+    };
+
     "test random generated"_test = [] {
         session_id sid1;
         session_id sid2;