UnleashedRecomp/tools/patches/xenonrecomp-ios-streaming-memory-map.patch

diff --git a/XenonUtils/memory_mapped_file.cpp b/XenonUtils/memory_mapped_file.cpp
index ba3c5d8..530321d 100644
--- a/XenonUtils/memory_mapped_file.cpp
+++ b/XenonUtils/memory_mapped_file.cpp
@@ -1,5 +1,7 @@
 #include "memory_mapped_file.h"
 
+#include <algorithm>
+
 #if !defined(_WIN32)
 #   include <cstring>
 #   include <cstdio>
@@ -34,14 +36,19 @@ MemoryMappedFile::MemoryMappedFile(MemoryMappedFile &&other)
     other.fileMappingHandle = nullptr;
     other.fileView = nullptr;
     other.fileSize.QuadPart = 0;
+    other.streamingMode = false;
 #else
     fileHandle = other.fileHandle;
     fileView = other.fileView;
     fileSize = other.fileSize;
+    mappedLength = other.mappedLength;
+    streamingMode = other.streamingMode;
 
     other.fileHandle = -1;
     other.fileView = MAP_FAILED;
     other.fileSize = 0;
+    other.mappedLength = 0;
+    other.streamingMode = false;
 #endif
 }
 
@@ -103,14 +110,23 @@ bool MemoryMappedFile::open(const std::filesystem::path &path)
     }
 
     fileView = mmap(nullptr, fileSize, PROT_READ, MAP_PRIVATE, fileHandle, 0);
-    if (fileView == MAP_FAILED)
+    if (fileView != MAP_FAILED)
     {
-        fprintf(stderr, "mmap failed with error %s.\n", strerror(errno));
-        ::close(fileHandle);
-        fileHandle = -1;
-        return false;
+        mappedLength = fileSize;
+        return true;
     }
 
+    static constexpr size_t PartialMapSize = 128 * 1024 * 1024;
+    const size_t partialMapSize = std::min(static_cast<size_t>(fileSize), PartialMapSize);
+    fileView = mmap(nullptr, partialMapSize, PROT_READ, MAP_PRIVATE, fileHandle, 0);
+    if (fileView != MAP_FAILED)
+    {
+        mappedLength = static_cast<off_t>(partialMapSize);
+        return true;
+    }
+
+    fprintf(stderr, "mmap failed with error %s, falling back to streaming I/O.\n", strerror(errno));
+    streamingMode = true;
     return true;
 #endif
 }
@@ -135,7 +151,7 @@ void MemoryMappedFile::close()
 #else
     if (fileView != MAP_FAILED)
     {
-        munmap(fileView, fileSize);
+        munmap(fileView, mappedLength);
     }
 
     if (fileHandle != -1)
@@ -148,14 +164,86 @@ void MemoryMappedFile::close()
 bool MemoryMappedFile::isOpen() const
 {
 #if defined(_WIN32)
-    return (fileView != nullptr);
+    return (fileView != nullptr) || (streamingMode && fileHandle != nullptr);
+#else
+    return (fileView != MAP_FAILED) || (streamingMode && fileHandle != -1);
+#endif
+}
+
+bool MemoryMappedFile::readAt(size_t offset, void *buffer, size_t size) const
+{
+    if (!isOpen() || buffer == nullptr)
+        return false;
+
+    if (static_cast<off_t>(offset) < 0 || static_cast<off_t>(offset + size) > fileSize)
+        return false;
+
+#if defined(_WIN32)
+    if (fileView != nullptr)
+    {
+        memcpy(buffer, reinterpret_cast<const uint8_t *>(fileView) + offset, size);
+        return true;
+    }
+
+    if (!streamingMode || fileHandle == nullptr)
+        return false;
+
+    OVERLAPPED overlapped = {};
+    overlapped.Offset = static_cast<DWORD>(offset & 0xFFFFFFFF);
+    overlapped.OffsetHigh = static_cast<DWORD>(offset >> 32);
+    DWORD bytesRead = 0;
+    if (!ReadFile(fileHandle, buffer, static_cast<DWORD>(size), &bytesRead, &overlapped) || bytesRead != size)
+        return false;
+
+    return true;
 #else
-    return (fileView != MAP_FAILED);
+    if (fileView != MAP_FAILED)
+    {
+        const size_t mappedEnd = static_cast<size_t>(mappedLength);
+        if (offset + size <= mappedEnd)
+        {
+            memcpy(buffer, reinterpret_cast<const uint8_t *>(fileView) + offset, size);
+            return true;
+        }
+
+        if (offset >= mappedEnd)
+        {
+            return pread(fileHandle, buffer, size, static_cast<off_t>(offset)) == static_cast<ssize_t>(size);
+        }
+
+        const size_t mappedBytes = mappedEnd - offset;
+        memcpy(buffer, reinterpret_cast<const uint8_t *>(fileView) + offset, mappedBytes);
+        const size_t remainingBytes = size - mappedBytes;
+        return pread(fileHandle, static_cast<uint8_t *>(buffer) + mappedBytes, remainingBytes, static_cast<off_t>(mappedEnd)) == static_cast<ssize_t>(remainingBytes);
+    }
+
+    if (!streamingMode || fileHandle == -1)
+        return false;
+
+    size_t bytesRead = 0;
+    while (bytesRead < size)
+    {
+        const ssize_t result = pread(fileHandle, static_cast<uint8_t *>(buffer) + bytesRead, size - bytesRead, static_cast<off_t>(offset + bytesRead));
+        if (result <= 0)
+            return false;
+
+        bytesRead += static_cast<size_t>(result);
+    }
+
+    return true;
 #endif
 }
 
 uint8_t *MemoryMappedFile::data() const
 {
+#if defined(_WIN32)
+    if (fileView == nullptr)
+        return nullptr;
+#else
+    if (fileView == MAP_FAILED)
+        return nullptr;
+#endif
+
     return reinterpret_cast<uint8_t *>(fileView);
 }
 
diff --git a/XenonUtils/memory_mapped_file.h b/XenonUtils/memory_mapped_file.h
index a3de88b..640cc42 100644
--- a/XenonUtils/memory_mapped_file.h
+++ b/XenonUtils/memory_mapped_file.h
@@ -14,10 +14,13 @@ struct MemoryMappedFile {
     HANDLE fileMappingHandle = nullptr;
     LPVOID fileView = nullptr;
     LARGE_INTEGER fileSize = {};
+    bool streamingMode = false;
 #else
     int fileHandle = -1;
     void *fileView = MAP_FAILED;
     off_t fileSize = 0;
+    off_t mappedLength = 0;
+    bool streamingMode = false;
 #endif
 
     MemoryMappedFile();
@@ -27,6 +30,7 @@ struct MemoryMappedFile {
     bool open(const std::filesystem::path &path);
     void close();
     bool isOpen() const;
+    bool readAt(size_t offset, void *buffer, size_t size) const;
     uint8_t *data() const;
     size_t size() const;
 };