1 files changed, 162 insertions, 0 deletions
diff --git a/Source/UnitTests/Common/LazyMemoryRegionBitSetTest.cpp b/Source/UnitTests/Common/LazyMemoryRegionBitSetTest.cpp
new file mode 100644
index 0000000000..e9b9a12716
--- /dev/null
+++ b/Source/UnitTests/Common/LazyMemoryRegionBitSetTest.cpp
@@ -0,0 +1,162 @@
+// Copyright 2026 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <fmt/format.h>
+#include <gtest/gtest.h>
+
+#include "Common/LazyMemoryRegionBitSet.h"
+#include "Common/MemArena.h"
+
+// Intentionally not divisible by 8
+static constexpr size_t BIT_COUNT = 1024 + 512 + 1;
+
+// Two blocks for the test to write to, and one block that remains mapped to the default page so we
+// can check that we didn't accidentally write to the default page
+static constexpr size_t WINDOWS_BOUNDARY_BIT_COUNT =
+    Common::LazyMemoryRegion::WINDOWS_BLOCK_SIZE * 8 * 3;
+
+static u32 ExpectedContentAllZeroes(size_t)
+{
+  return 0;
+}
+
+static u32 ExpectedContentAllOnes(size_t)
+{
+  return 0xFFFFFFFF;
+}
+
+static u32 ExpectedContentAfterSetting(size_t index)
+{
+  switch (index)
+  {
+  case 32:
+    return 0x0000FF00;
+  case 34:
+    return 0x0FFFFFF0;
+  case 35:
+    return 0xFFFFFFF0;
+  case 36:
+    return 0x0FFFFFFF;
+  case 37:
+    return 0xFFFFFFF0;
+  case 39:
+    return 0x0FFFFFFF;
+  case 40:
+    return 0xFFFFFFF0;
+  case 47:
+    return 0x0FFFFFFF;
+  default:
+    if (index < 32)
+      return 1 << index;
+    if (index < 48)
+      return 0xFFFFFFFF;
+    return 0;
+  }
+}
+
+static u32 ExpectedContentAfterClearing(size_t index)
+{
+  return ~ExpectedContentAfterSetting(index);
+}
+
+static u32 ExpectedContentForWindowsBoundary(size_t index)
+{
+  switch (index)
+  {
+  case Common::LazyMemoryRegion::WINDOWS_BLOCK_SIZE / sizeof(u32) - 1:
+    return 0x80000000;
+  case Common::LazyMemoryRegion::WINDOWS_BLOCK_SIZE / sizeof(u32):
+    return 0x00000001;
+  default:
+    return 0;
+  }
+}
+
+template <typename F>
+static void VerifyContent(const u32* memory, size_t bits, F f)
+{
+  const size_t end_index = bits / 32;
+  for (size_t i = 0; i < end_index; ++i, ++memory)
+  {
+    const u32 expected = f(i);
+    ASSERT_EQ(*memory, expected) << "i=" << i;
+  }
+  if (bits % 32 != 0)
+  {
+    const u32 expected = f(end_index) & ~(0xFFFFFFFF << bits % 32);
+    ASSERT_EQ(*memory, expected) << "i=" << end_index;
+  }
+}
+
+TEST(LazyMemoryRegionBitSet, Unwritten)
+{
+  Common::LazyMemoryRegionBitSet bit_set(BIT_COUNT);
+  VerifyContent(bit_set.GetRawMemory(), BIT_COUNT, ExpectedContentAllZeroes);
+}
+
+TEST(LazyMemoryRegionBitSet, Set)
+{
+  Common::LazyMemoryRegionBitSet bit_set(BIT_COUNT);
+
+  // Set single bits in the range 0-1023
+  for (size_t i = 0; i < 32; ++i)
+    bit_set.SetBit(i * 33);
+
+  // Set ranges of bits in bits 1024 and higher
+  bit_set.SetBits(1024 + 8, 1024 + 16);
+  bit_set.SetBits(1024 + 32, 1024 + 64);
+  bit_set.SetBits(1024 + 68, 1024 + 92);
+  bit_set.SetBits(1024 + 100, 1024 + 128);
+  bit_set.SetBits(1024 + 128, 1024 + 156);
+  bit_set.SetBits(1024 + 164, 1024 + 252);
+  bit_set.SetBits(1024 + 260, 1024 + 384);
+  bit_set.SetBits(1024 + 384, 1024 + 508);
+
+  VerifyContent(bit_set.GetRawMemory(), BIT_COUNT, ExpectedContentAfterSetting);
+
+  bit_set.Clear();
+  VerifyContent(bit_set.GetRawMemory(), BIT_COUNT, ExpectedContentAllZeroes);
+}
+
+TEST(LazyMemoryRegionBitSet, Clear)
+{
+  Common::LazyMemoryRegionBitSet bit_set(BIT_COUNT);
+  bit_set.SetBits(0, BIT_COUNT);
+  VerifyContent(bit_set.GetRawMemory(), BIT_COUNT, ExpectedContentAllOnes);
+
+  // Clear single bits in the range 0-1023
+  for (size_t i = 0; i < 32; ++i)
+    bit_set.ClearBit(i * 33);
+
+  // Clear ranges of bits in bits 1024 and higher
+  bit_set.ClearBits(1024 + 8, 1024 + 16);
+  bit_set.ClearBits(1024 + 32, 1024 + 64);
+  bit_set.ClearBits(1024 + 68, 1024 + 92);
+  bit_set.ClearBits(1024 + 100, 1024 + 128);
+  bit_set.ClearBits(1024 + 128, 1024 + 156);
+  bit_set.ClearBits(1024 + 164, 1024 + 252);
+  bit_set.ClearBits(1024 + 260, 1024 + 384);
+  bit_set.ClearBits(1024 + 384, 1024 + 508);
+
+  VerifyContent(bit_set.GetRawMemory(), BIT_COUNT, ExpectedContentAfterClearing);
+
+  bit_set.Clear();
+  VerifyContent(bit_set.GetRawMemory(), BIT_COUNT, ExpectedContentAllZeroes);
+}
+
+TEST(LazyMemoryRegionBitSet, WindowsBoundary)
+{
+  // Unlike on other operating systems, LazyMemoryRegion's Windows implementation allocates one page
+  // containing only zeroes and maps it to every part of the region by default. If
+  // LazyMemoryRegionBitSet wants to write to any part of the region, it first needs to call
+  // LazyMemoryRegion::EnsureMemoryPageWritable. This test is checking that
+  // LazyMemoryRegion::EnsureMemoryPageWritable is being called with the correct parameters.
+
+  Common::LazyMemoryRegionBitSet bit_set(WINDOWS_BOUNDARY_BIT_COUNT);
+
+  bit_set.SetBits(Common::LazyMemoryRegion::WINDOWS_BLOCK_SIZE * 8 - 1,
+                  Common::LazyMemoryRegion::WINDOWS_BLOCK_SIZE * 8 + 1);
+
+  VerifyContent(bit_set.GetRawMemory(), WINDOWS_BOUNDARY_BIT_COUNT,
+                ExpectedContentForWindowsBoundary);
+}