From b3fb6bd99041ad26768800f0e624e23b85add362 Mon Sep 17 00:00:00 2001
From: Chocobo1 <Chocobo1@users.noreply.github.com>
Date: Sat, 12 Mar 2022 21:40:58 +0800
Subject: [PATCH] Avoid redundant hashing

The return type of `std::hash()` is larger (or equal) than what
`qHash()` requires so we can omit hashing it again.
---
 src/base/bittorrent/infohash.cpp |  2 +-
 src/base/bittorrent/ltqhash.h    | 12 ++++--------
 src/base/digest32.h              | 14 +++++++++-----
 3 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/src/base/bittorrent/infohash.cpp b/src/base/bittorrent/infohash.cpp
index 2f5943fe8..7fa78b233 100644
--- a/src/base/bittorrent/infohash.cpp
+++ b/src/base/bittorrent/infohash.cpp
@@ -96,7 +96,7 @@ std::size_t BitTorrent::qHash(const BitTorrent::TorrentID &key, const std::size_
 uint BitTorrent::qHash(const BitTorrent::TorrentID &key, const uint seed)
 #endif
 {
-    return ::qHash(std::hash<TorrentID::UnderlyingType>()(key), seed);
+    return ::qHash(static_cast<TorrentID::BaseType>(key), seed);
 }
 
 bool BitTorrent::operator==(const BitTorrent::InfoHash &left, const BitTorrent::InfoHash &right)
diff --git a/src/base/bittorrent/ltqhash.h b/src/base/bittorrent/ltqhash.h
index a86da8a6a..b8a929b32 100644
--- a/src/base/bittorrent/ltqhash.h
+++ b/src/base/bittorrent/ltqhash.h
@@ -28,28 +28,24 @@
 
 #pragma once
 
+#include <QtGlobal>
+
+#if (QT_VERSION < QT_VERSION_CHECK(6, 0, 0))
 #include <functional>
 
 #include <libtorrent/units.hpp>
 
-#include <QtGlobal>
 #include <QHash>
 
-// From https://doc.qt.io/qt-6/qhash.html#the-hashing-function:
-// A hashing function for a key type K may be provided in two different ways.
-// The first way is by having an overload of qHash() in K's namespace.
 namespace libtorrent
 {
     namespace aux
     {
         template <typename T, typename Tag>
-#if (QT_VERSION >= QT_VERSION_CHECK(6, 0, 0))
-        std::size_t qHash(const strong_typedef<T, Tag> &key, const std::size_t seed = 0)
-#else
         uint qHash(const strong_typedef<T, Tag> &key, const uint seed = 0)
-#endif
         {
             return ::qHash((std::hash<strong_typedef<T, Tag>> {})(key), seed);
         }
     }
 }
+#endif
diff --git a/src/base/digest32.h b/src/base/digest32.h
index ae67458eb..111f82e60 100644
--- a/src/base/digest32.h
+++ b/src/base/digest32.h
@@ -131,12 +131,16 @@ bool operator<(const Digest32<N> &left, const Digest32<N> &right)
             < static_cast<typename Digest32<N>::UnderlyingType>(right);
 }
 
-template <int N>
 #if (QT_VERSION >= QT_VERSION_CHECK(6, 0, 0))
+template <int N>
 std::size_t qHash(const Digest32<N> &key, const std::size_t seed = 0)
-#else
-uint qHash(const Digest32<N> &key, const uint seed = 0)
-#endif
 {
-    return ::qHash(std::hash<typename Digest32<N>::UnderlyingType>()(key), seed);
+    return ::qHash(static_cast<typename Digest32<N>::UnderlyingType>(key), seed);
 }
+#else
+template <int N>
+uint qHash(const Digest32<N> &key, const uint seed = 0)
+{
+    return static_cast<uint>((std::hash<typename Digest32<N>::UnderlyingType> {})(key)) ^ seed;
+}
+#endif