Class MemoryMappedFile

Source/ThirdParty/tinyexr.h:8258–8447

Represents a read-only file mapped to an address space in memory. If no memory-mapping API is available, falls back to allocating a buffer with a copy of the file's data.

// If no memory-mapping API is available, falls back to allocating a buffer
// with a copy of the file's data.
struct MemoryMappedFile {
  unsigned char *data;  // To the start of the file's data.
  size_t size;          // The size of the file in bytes.
#ifdef TINYEXR_USE_WIN32_MMAP
  HANDLE windows_file;
  HANDLE windows_file_mapping;
#elif defined(TINYEXR_USE_POSIX_MMAP)
  int posix_descriptor;
#endif

  // MemoryMappedFile's constructor tries to map memory to a file.
  // If this succeeds, valid() will return true and all fields
  // are usable; otherwise, valid() will return false.
  MemoryMappedFile(const char *filename) {
    data = NULL;
    size = 0;
#ifdef TINYEXR_USE_WIN32_MMAP
    windows_file_mapping = NULL;
    windows_file =
        CreateFileW(tinyexr::UTF8ToWchar(filename).c_str(),  // lpFileName
                    GENERIC_READ,                            // dwDesiredAccess
                    FILE_SHARE_READ,                         // dwShareMode
                    NULL,                     // lpSecurityAttributes
                    OPEN_EXISTING,            // dwCreationDisposition
                    FILE_ATTRIBUTE_READONLY,  // dwFlagsAndAttributes
                    NULL);                    // hTemplateFile
    if (windows_file == INVALID_HANDLE_VALUE) {
      return;
    }

    windows_file_mapping = CreateFileMapping(windows_file,  // hFile
                                             NULL,  // lpFileMappingAttributes
                                             PAGE_READONLY,  // flProtect
                                             0,      // dwMaximumSizeHigh
                                             0,      // dwMaximumSizeLow
                                             NULL);  // lpName
    if (windows_file_mapping == NULL) {
      return;
    }

    data = reinterpret_cast<unsigned char *>(
        MapViewOfFile(windows_file_mapping,  // hFileMappingObject
                      FILE_MAP_READ,         // dwDesiredAccess
                      0,                     // dwFileOffsetHigh
                      0,                     // dwFileOffsetLow
                      0));                   // dwNumberOfBytesToMap
    if (!data) {
      return;
    }

    LARGE_INTEGER windows_file_size = {};
    if (!GetFileSizeEx(windows_file, &windows_file_size) ||
        static_cast<ULONGLONG>(windows_file_size.QuadPart) >
            std::numeric_limits<size_t>::max()) {
      UnmapViewOfFile(data);
      data = NULL;
      return;
    }