A small bit of coverage cleanup (#38)

* Small fix for that weird Win32 VM line coverage

* More better

* Switch to a fast return layout

* And the partials reveal themselves

* I have a sneaking suspicion

* And the fix

Engine/Platform/System/Win32/CYBWin32VirtualMemory.cpp

@@ -7,6 +7,8 @@ unsigned int CYB::Platform::System::Implementation::VirtualMemory::SystemPageSiz
 }
 
 void* CYB::Platform::System::Implementation::VirtualMemory::PageAlignedUpperBound(void* AMemory, const unsigned int APageSize) noexcept {
+	if ((reinterpret_cast<unsigned long long>(AMemory) % APageSize) == 0)
+		return AMemory;
 	return reinterpret_cast<void*>(reinterpret_cast<unsigned long long>(AMemory) + (APageSize - (reinterpret_cast<unsigned long long>(AMemory) % APageSize)));
 }
 
@@ -68,16 +70,25 @@ void CYB::Platform::System::VirtualMemory::Discard(void* const AMemory, const un
 	API::Assert::LessThanOrEqual(static_cast<byte*>(FReservation), static_cast<byte*>(AMemory));
 	API::Assert::LessThanOrEqual(static_cast<byte*>(AMemory), static_cast<byte*>(FReservation) + FCommitSize);
 	API::Assert::LessThanOrEqual(static_cast<byte*>(AMemory) + ANumBytes, static_cast<byte*>(FReservation) + FCommitSize);
+
+	if (!Core().FModuleManager.FK32Extended.Loaded<Modules::Kernel32Extended::DiscardVirtualMemory>())
+		return;
+
 	const auto PageSize(Implementation::VirtualMemory::SystemPageSize());
-	if (ANumBytes >= PageSize) {
-		auto const AlignedMemory(Implementation::VirtualMemory::PageAlignedUpperBound(AMemory, PageSize));
-		const auto Difference(reinterpret_cast<unsigned long long>(AlignedMemory) - reinterpret_cast<unsigned long long>(AMemory));
-		if (Difference < ANumBytes) {
-			const auto BytesAvailableToDiscard(ANumBytes - Difference);
-			const auto TrueDiscardSize(BytesAvailableToDiscard - (BytesAvailableToDiscard % PageSize));
-			if(TrueDiscardSize >= PageSize
-				&& Core().FModuleManager.FK32Extended.Loaded<Modules::Kernel32Extended::DiscardVirtualMemory>())
-					Core().FModuleManager.FK32Extended.Call<Modules::Kernel32Extended::DiscardVirtualMemory>(AlignedMemory, TrueDiscardSize);
-		}
-	}
+	if (ANumBytes < PageSize)
+		return;
+
+	auto const AlignedMemory(Implementation::VirtualMemory::PageAlignedUpperBound(AMemory, PageSize));
+	const auto Difference(reinterpret_cast<unsigned long long>(AlignedMemory) - reinterpret_cast<unsigned long long>(AMemory));
+
+	//Difference is inherently < PageSize
+
+	const auto BytesAvailableToDiscard(ANumBytes - Difference);
+
+	if (BytesAvailableToDiscard < PageSize)
+		return;
+
+	const auto TrueDiscardSize(BytesAvailableToDiscard - (BytesAvailableToDiscard % PageSize));
+
+	Core().FModuleManager.FK32Extended.Call<Modules::Kernel32Extended::DiscardVirtualMemory>(AlignedMemory, TrueDiscardSize);
 }

Engine/Platform/System/Win32/CYBWin32VirtualMemory.hpp

@@ -15,7 +15,7 @@ namespace CYB {
 					*/
 					static unsigned int SystemPageSize(void) noexcept;
 					/*!
-						@brief Get the base address of a page given an address
+						@brief Get the base address of a page on or after a given address
 						@param AMemory The address to reference
 						@param APageSize The system page size
 						@return The base address of the page @p AMemory lies on

Tests/Platform/System/VirtualMemory.cpp

@@ -92,19 +92,51 @@ SCENARIO("VirtualMemory reservation protection levels can be changed", "[Platfor
 		}
 	}
 }
+REDIRECTED_FUNCTION(BadDiscardVirtualMemory, void* const, const unsigned long long) {
+	return 0;
+}
 SCENARIO("VirtualMemory can be discarded and reused","[Platform][System][VirtualMemory][Unit]") {
 	ModuleDependancy<CYB::API::Platform::Identifier::WINDOWS, CYB::Platform::Modules::AMKernel32> K32(CYB::Core().FModuleManager.FK32);
 	ModuleDependancy<CYB::API::Platform::Identifier::WINDOWS, CYB::Platform::Modules::AMKernel32Extended> K32E(CYB::Core().FModuleManager.FK32Extended);
 	ModuleDependancy<CYB::API::Platform::POSIX, CYB::Platform::Modules::AMLibC> LibC(CYB::Core().FModuleManager.FC);
+#ifdef TARGET_OS_WINDOWS
+	//For testing purposes, assume it's not there
+	auto Thing(K32E.Redirect<CYB::Platform::Modules::Kernel32Extended::DiscardVirtualMemory, BadDiscardVirtualMemory>());
+#endif
 	GIVEN("A standard reservation and commit which has some data written to it") {
 		CYB::Platform::System::VirtualMemory Reservation(1000000);
 		Reservation.Commit(500000);
 		*static_cast<unsigned long long*>(Reservation()) = 1234;
 		WHEN("The memory is discarded") {
-			REQUIRE_NOTHROW(Reservation.Discard(Reservation(), 500000));
-			THEN("No errors occur and pages can be reused but data may differ") {
-				CHECK_NOTHROW(*static_cast<unsigned long long*>(Reservation()) = 5678);
-			}
+			auto DiscardSize(250000U);
+			auto DiscardPoint(Reservation());
+			const auto Then([&]() {
+				REQUIRE_NOTHROW(Reservation.Discard(DiscardPoint, DiscardSize));
+				THEN("No errors occur and pages can be reused but data may differ") {
+					CHECK_NOTHROW(*static_cast<unsigned long long*>(Reservation()) = 5678);
+				}
+			});
+			Then();
+			AND_WHEN("The discard size is low") {
+				DiscardSize = 12;
+				Then();
+			}
+			AND_WHEN("The discard point is close the end of the a page") {
+				DiscardPoint = static_cast<char*>(DiscardPoint) + 4090;
+				Then();
+			}
+			AND_WHEN("The discard size is okay but crosses a page boundary") {
+				DiscardSize = 5000;
+				DiscardPoint = static_cast<char*>(DiscardPoint) + 1500;
+				Then();
+			}
+#ifdef TARGET_OS_WINDOWS
+			AND_WHEN("The discard function does not exist") {
+				using RedirectType = CallRedirect<CYB::Platform::Modules::AMKernel32Extended, CYB::Platform::Modules::Kernel32Extended::DiscardVirtualMemory>;
+				RedirectType DoIt(CYB::Core().FModuleManager.FK32Extended, static_cast<RedirectType::FCallable*>(nullptr));
+				Then();
+			}
+#endif
 		}
 	}
 }