diff --git a/include/fast_io_core.h b/include/fast_io_core.h
index ba5a5fc9..e2ed5141 100644
--- a/include/fast_io_core.h
+++ b/include/fast_io_core.h
@@ -9,10 +9,13 @@
 #if !defined(__cpp_concepts)
 #error "fast_io requires at least C++20 standard compiler."
 #else
+
+#include <version>
+#include <cstdint>
+#include <cstddef>
+#include <climits>
 #include <bit>
 #include <limits>
-#include <cstdint>
-#include <version>
 
 #if __cpp_lib_three_way_comparison >= 201907L
 #include <compare>
diff --git a/include/fast_io_core_impl/char_category/char_category.h b/include/fast_io_core_impl/char_category/char_category.h
index f525a447..03faa7e7 100644
--- a/include/fast_io_core_impl/char_category/char_category.h
+++ b/include/fast_io_core_impl/char_category/char_category.h
@@ -1795,7 +1795,7 @@ inline constexpr bool is_html_whitespace_wide_impl(wchar_t ch) noexcept
 	};
 }
 
-inline constexpr bool is_dos_path_invalid_character_impl(char32_t ch) noexcept
+inline constexpr bool is_dos_file_invalid_character_impl(char32_t ch) noexcept
 {
 	if (ch < static_cast<char32_t>(32u))
 	{
@@ -1926,15 +1926,15 @@ To do: to_c_fullwidth
 */
 
 template <::std::integral T>
-inline constexpr bool is_dos_path_invalid_character(T ch) noexcept
+inline constexpr bool is_dos_file_invalid_character(T ch) noexcept
 {
 	if constexpr (::std::signed_integral<T>)
 	{
-		return ::fast_io::char_category::details::is_dos_path_invalid_character_impl(static_cast<char32_t>(static_cast<::std::make_unsigned_t<T>>(ch)));
+		return ::fast_io::char_category::details::is_dos_file_invalid_character_impl(static_cast<char32_t>(static_cast<::std::make_unsigned_t<T>>(ch)));
 	}
 	else
 	{
-		return ::fast_io::char_category::details::is_dos_path_invalid_character_impl(static_cast<char32_t>(ch));
+		return ::fast_io::char_category::details::is_dos_file_invalid_character_impl(static_cast<char32_t>(ch));
 	}
 }
 
diff --git a/include/fast_io_core_impl/char_category/char_category_traits.h b/include/fast_io_core_impl/char_category/char_category_traits.h
index fd637cea..574493e2 100644
--- a/include/fast_io_core_impl/char_category/char_category_traits.h
+++ b/include/fast_io_core_impl/char_category/char_category_traits.h
@@ -19,7 +19,7 @@ enum class char_category_family : ::std::uint_least32_t
 	c_space,                    // Whitespace characters (space, tab, newline, etc.)
 	c_upper,                    // Uppercase alphabetic characters
 	c_xdigit,                   // Hexadecimal digits (0-9, A-F, a-f)
-	dos_path_invalid_character, // DOS Path invalid character
+	dos_file_invalid_character, // DOS Path invalid character
 	html_whitespace             // HTML whitespace
 };
 
@@ -96,9 +96,9 @@ class char_category_traits
 		{
 			ret = ::fast_io::char_category::is_c_fullwidth(ch);
 		}
-		else if constexpr (fam == ::fast_io::char_category::char_category_family::dos_path_invalid_character)
+		else if constexpr (fam == ::fast_io::char_category::char_category_family::dos_file_invalid_character)
 		{
-			ret = ::fast_io::char_category::is_dos_path_invalid_character(ch);
+			ret = ::fast_io::char_category::is_dos_file_invalid_character(ch);
 		}
 		if constexpr (negate)
 		{
@@ -192,7 +192,7 @@ using c_punct = ::fast_io::char_category::char_category_traits<::fast_io::char_c
 using c_space = ::fast_io::char_category::char_category_traits<::fast_io::char_category::char_category_family::c_space, false>;
 using c_upper = ::fast_io::char_category::char_category_traits<::fast_io::char_category::char_category_family::c_upper, false>;
 using c_xdigit = ::fast_io::char_category::char_category_traits<::fast_io::char_category::char_category_family::c_xdigit, false>;
-using dos_path_invalid_character = ::fast_io::char_category::char_category_traits<::fast_io::char_category::char_category_family::dos_path_invalid_character, false>;
+using dos_file_invalid_character = ::fast_io::char_category::char_category_traits<::fast_io::char_category::char_category_family::dos_file_invalid_character, false>;
 using html_whitespace = ::fast_io::char_category::char_category_traits<::fast_io::char_category::char_category_family::html_whitespace, false>;
 
 
@@ -210,7 +210,7 @@ using not_c_punct = ::fast_io::char_category::char_category_traits<::fast_io::ch
 using not_c_space = ::fast_io::char_category::char_category_traits<::fast_io::char_category::char_category_family::c_space, true>;
 using not_c_upper = ::fast_io::char_category::char_category_traits<::fast_io::char_category::char_category_family::c_upper, true>;
 using not_c_xdigit = ::fast_io::char_category::char_category_traits<::fast_io::char_category::char_category_family::c_xdigit, true>;
-using not_dos_path_invalid_character = ::fast_io::char_category::char_category_traits<::fast_io::char_category::char_category_family::dos_path_invalid_character, true>;
+using not_dos_file_invalid_character = ::fast_io::char_category::char_category_traits<::fast_io::char_category::char_category_family::dos_file_invalid_character, true>;
 using not_html_whitespace = ::fast_io::char_category::char_category_traits<::fast_io::char_category::char_category_family::html_whitespace, true>;
 
 namespace details
diff --git a/include/fast_io_device.h b/include/fast_io_device.h
index cc4b4d4f..cc663b16 100644
--- a/include/fast_io_device.h
+++ b/include/fast_io_device.h
@@ -29,6 +29,20 @@ using dir_file = directory_file_wrapper<
 #endif
 	>;
 
+// Note:
+// The Win32 API layer is not well-suited for precise "dirfile" semantics,
+// because it abstracts away the underlying NT object types. Unlike the NT I/O
+// manager (where FILE_DIRECTORY_FILE and FILE_NON_DIRECTORY_FILE flags enforce
+// strict open-type constraints), Win32’s CreateFileW does not distinguish
+// between files and directories unless explicitly checked afterwards.
+//
+// FILE_FLAG_BACKUP_SEMANTICS merely *permits* opening a directory handle,
+// but does not *require* the target to be a directory. Similarly, adding
+// FILE_ATTRIBUTE_DIRECTORY has no enforcement effect — it's only a metadata hint.
+// Therefore, to emulate dirfile-style correctness, one must explicitly query
+// the object type (e.g., via GetFileInformationByHandle or GetFileAttributes)
+// after opening the handle.
+
 /*
 template region
 */
diff --git a/include/fast_io_driver/install_path/impl.h b/include/fast_io_driver/install_path/impl.h
index a4adc88d..4d2635e8 100644
--- a/include/fast_io_driver/install_path/impl.h
+++ b/include/fast_io_driver/install_path/impl.h
@@ -2,15 +2,15 @@
 
 #include"install_path.h"
 
-#if defined(_WIN32)
+#if defined(_WIN32) || defined(__CYGWIN__)
 #include "argv0_null.h"
 #else
 #include "argv0.h"
 #endif
 
-#if (defined(__linux) || defined(__linux__) || defined(__gnu_linux__)) || defined(__CYGWIN__) || defined(__sun)
+#if (defined(__linux) || defined(__linux__) || defined(__gnu_linux__)) || defined(__sun)
 #include "linux.h"
-#elif defined(_WIN32)
+#elif defined(_WIN32) || defined(__CYGWIN__)
 #if defined(_WIN32_WINDOWS)
 #include "win32_9xa.h"
 #else
diff --git a/include/fast_io_dsal/impl/misc/push_macros.h b/include/fast_io_dsal/impl/misc/push_macros.h
index 4e2b06c7..1082f819 100644
--- a/include/fast_io_dsal/impl/misc/push_macros.h
+++ b/include/fast_io_dsal/impl/misc/push_macros.h
@@ -14,7 +14,14 @@
 #undef move
 
 #pragma push_macro("new")
+#if __GNUC__ >= 16
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wkeyword-macro"
 #undef new
+#pragma GCC diagnostic pop
+#else
+#undef new
+#endif
 
 #pragma push_macro("refresh")
 #undef refresh
diff --git a/include/fast_io_hosted/dll/win32.h b/include/fast_io_hosted/dll/win32.h
index 58ef7b30..4e31cb98 100644
--- a/include/fast_io_hosted/dll/win32.h
+++ b/include/fast_io_hosted/dll/win32.h
@@ -98,7 +98,7 @@ inline void *create_win32_dll_9xa(char const *filename) // 9x kernel does not su
 inline void *create_win32_dll_ntw(char16_t const *filename, [[maybe_unused]] dll_mode mode)
 {
 	auto hmodule{
-#if _WIN32_WINNT <= 0x0500
+#if (defined(_WIN32_WINNT) && _WIN32_WINNT <= 0x0500)
 		// Windows 2000 does not support Ex apis
 		::fast_io::win32::LoadLibraryW(filename)
 #else
diff --git a/include/fast_io_hosted/filesystem/dos.h b/include/fast_io_hosted/filesystem/dos.h
index 0f236cf8..e1f3dfcc 100644
--- a/include/fast_io_hosted/filesystem/dos.h
+++ b/include/fast_io_hosted/filesystem/dos.h
@@ -60,6 +60,8 @@ namespace posix
 // extern char const* my_dos_get_fd_name(int) noexcept __asm__("___get_fd_name");
 extern DIR *my_dos_opendir(char const *) noexcept __asm__("_opendir");
 
+extern int my_dos_closedir(DIR *) noexcept __asm__("_closedir");
+
 inline DIR *my_dos_fdopendir(int fd) noexcept
 {
 	return my_dos_opendir(::fast_io::noexcept_call(::__get_fd_name, fd));
@@ -69,6 +71,16 @@ inline DIR *my_dos_fdopendir(int fd) noexcept
 namespace details
 {
 
+inline void check_dos_fd_is_dir(int fd)
+{
+	auto const dir{::fast_io::posix::my_dos_fdopendir(fd)};
+	if (dir == nullptr) [[unlikely]]
+	{
+		throw_posix_error(ENOTDIR);
+	}
+	::fast_io::posix::my_dos_closedir(dir);
+}
+
 inline dos_DIR sys_dup_dir(dos_DIR dirp)
 {
 	if (dirp.dirp == nullptr) [[unlikely]]
@@ -127,7 +139,7 @@ class dos_directory_file FAST_IO_TRIVIALLY_RELOCATABLE_IF_ELIGIBLE : public dos_
 		auto newdir{details::sys_dup_dir(other.dirp)};
 		if (this->dirp.dirp) [[likely]]
 		{
-			noexcept_call(::closedir, this->dirp.dirp);
+			::fast_io::posix::my_dos_closedir(this->dirp.dirp);
 		}
 		if (this->dirp.fd != -1) [[likely]]
 		{
@@ -149,7 +161,7 @@ class dos_directory_file FAST_IO_TRIVIALLY_RELOCATABLE_IF_ELIGIBLE : public dos_
 		}
 		if (this->dirp.dirp) [[likely]]
 		{
-			noexcept_call(::closedir, this->dirp.dirp);
+			::fast_io::posix::my_dos_closedir(this->dirp.dirp);
 		}
 		if (this->dirp.fd != -1) [[likely]]
 		{
@@ -163,7 +175,7 @@ class dos_directory_file FAST_IO_TRIVIALLY_RELOCATABLE_IF_ELIGIBLE : public dos_
 	{
 		if (this->dirp.dirp) [[likely]]
 		{
-			noexcept_call(::closedir, this->dirp.dirp);
+			::fast_io::posix::my_dos_closedir(this->dirp.dirp);		
 		}
 		if (this->dirp.fd != -1) [[likely]]
 		{
@@ -177,7 +189,7 @@ class dos_directory_file FAST_IO_TRIVIALLY_RELOCATABLE_IF_ELIGIBLE : public dos_
 		if (*this) [[likely]]
 		{
 			int fd_to_close{this->dirp.fd};
-			int ret{noexcept_call(::closedir, this->dirp.dirp)};
+			int ret{::fast_io::posix::my_dos_closedir(this->dirp.dirp)};
 			this->dirp.dirp = nullptr;
 			this->dirp.fd = -1;
 			if (fd_to_close != -1)
@@ -195,7 +207,7 @@ class dos_directory_file FAST_IO_TRIVIALLY_RELOCATABLE_IF_ELIGIBLE : public dos_
 	{
 		if (this->dirp.dirp) [[likely]]
 		{
-			noexcept_call(::closedir, this->dirp.dirp);
+			::fast_io::posix::my_dos_closedir(this->dirp.dirp);
 		}
 		if (this->dirp.fd != -1) [[likely]]
 		{
diff --git a/include/fast_io_hosted/filesystem/nt_at.h b/include/fast_io_hosted/filesystem/nt_at.h
index 802eb55e..3be2375a 100644
--- a/include/fast_io_hosted/filesystem/nt_at.h
+++ b/include/fast_io_hosted/filesystem/nt_at.h
@@ -93,15 +93,21 @@ inline void nt_unlinkat_impl(void *dirhd, char16_t const *path_c_str, ::std::siz
 template <bool zw>
 inline void nt_mkdirat_impl(void *dirhd, char16_t const *path_c_str, ::std::size_t path_size, perms pm, bool kernel)
 {
-	constexpr fast_io::win32::nt::details::nt_open_mode create_dir_mode{
-		fast_io::win32::nt::details::calculate_nt_open_mode(
-			{fast_io::open_mode::creat | fast_io::open_mode::directory})};
-	auto m_dir_mode{create_dir_mode};
+	nt_open_mode m_dir_mode{
+		.DesiredAccess = 0x00100000 | 0x0001, // SYNCHRONIZE | FILE_LIST_DIRECTORY
+		.FileAttributes = 0x80,               // FILE_ATTRIBUTE_NORMAL
+		.ShareAccess = 0x00000003,            // FILE_SHARE_READ | FILE_SHARE_WRITE
+		.CreateDisposition = 0x00000002,      // CREATE_NEW	=>	FILE_CREATE		(0x00000002)
+		.CreateOptions = 0x00004021           // FILE_DIRECTORY_FILE | FILE_SYNCHRONOUS_IO_NONALERT | FILE_OPEN_FOR_BACKUP_INTENT
+	};
+
 	if ((pm & perms::owner_write) == perms::none)
 	{
 		m_dir_mode.FileAttributes |= 0x00000001; // FILE_ATTRIBUTE_READONLY
 	}
+
 	auto status{nt_close<zw>(nt_call_determine_kernel_callback(dirhd, path_c_str, path_size, kernel, nt_create_callback<zw>{m_dir_mode}))};
+	
 	if (status)
 	{
 		throw_nt_error(status);
@@ -775,7 +781,7 @@ inline ::fast_io::details::basic_ct_string<char_type> nt_readlinkat_impl(void *d
 		.FileAttributes = 0x80,               // FILE_ATTRIBUTE_NORMAL
 		.ShareAccess = 0x00000007,            // FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE
 		.CreateDisposition = 0x00000001,      // OPEN_EXISTING => FILE_OPEN
-		.CreateOptions = 0x00200000           // FILE_FLAG_OPEN_REPARSE_POINT => FILE_OPEN_REPARSE_POINT (0x00200000)
+		.CreateOptions = 0x00200000 | 0x00000020 // FILE_FLAG_OPEN_REPARSE_POINT | FILE_SYNCHRONOUS_IO_NONALERT
 	};
 
 	::fast_io::basic_nt_family_file<(zw ? nt_family::zw : nt_family::nt), char> file{
diff --git a/include/fast_io_hosted/filesystem/posix.h b/include/fast_io_hosted/filesystem/posix.h
index 19776fad..e8940aa2 100644
--- a/include/fast_io_hosted/filesystem/posix.h
+++ b/include/fast_io_hosted/filesystem/posix.h
@@ -6,6 +6,28 @@ namespace fast_io
 
 namespace details
 {
+#if defined(__CYGWIN__)
+struct my_cygwin_DIR
+{
+  /* This is first to set alignment in non _LIBC case.  */
+  unsigned long	__d_cookie;
+  struct dirent	*__d_dirent;
+  char		*__d_dirname;		/* use for internal caching */
+  ::std::int32_t	 __d_position;		/* used by telldir/seekdir */
+  int		 __d_fd;
+  ::std::uintptr_t	 __d_internal;
+  void		*__handle;
+  void		*__fh;
+  unsigned	 __flags;
+};
+
+using my_cygwin_DIR_may_alias_ptr = 
+#if __has_cpp_attribute(__gnu__::__may_alias__)
+	[[__gnu__::__may_alias__]]
+#endif
+	my_cygwin_DIR *;
+#endif
+
 inline int dirp_to_fd(DIR *dirp) noexcept
 {
 	if (dirp == nullptr)
@@ -13,7 +35,7 @@ inline int dirp_to_fd(DIR *dirp) noexcept
 		return -1;
 	}
 #if defined(__CYGWIN__)
-	return dirp->__d_fd;
+	return reinterpret_cast<my_cygwin_DIR_may_alias_ptr>(dirp)->__d_fd;
 #else
 	return dirfd(dirp);
 #endif
@@ -58,7 +80,7 @@ inline DIR *sys_dup_dir(DIR *dirp)
 	}
 	auto fd{
 #if defined(__CYGWIN__)
-		dirp->__d_fd
+		reinterpret_cast<my_cygwin_DIR_may_alias_ptr>(dirp)->__d_fd
 #else
 		dirfd(dirp)
 #endif
diff --git a/include/fast_io_hosted/filesystem/posix_at.h b/include/fast_io_hosted/filesystem/posix_at.h
index 04967922..9dbf5954 100644
--- a/include/fast_io_hosted/filesystem/posix_at.h
+++ b/include/fast_io_hosted/filesystem/posix_at.h
@@ -447,7 +447,7 @@ inline void posix_utimensat_impl(int dirfd, char const *path, unix_timestamp_opt
 }
 
 template<::std::integral char_type>
-inline ::fast_io::details::basic_ct_string<char_type> posix_readlinkat_impl(int dirfd, char const *pathname)
+inline ::fast_io::details::basic_ct_string<char_type> posix_readlinkat_impl([[maybe_unused]] int dirfd, [[maybe_unused]] char const *pathname)
 {
 #if defined(AT_SYMLINK_NOFOLLOW)
     using posix_ssize_t = ::std::make_signed_t<::std::size_t>;
diff --git a/include/fast_io_hosted/platforms/dos_filename.h b/include/fast_io_hosted/platforms/dos_filename.h
index dfb7fb1c..b890e339 100644
--- a/include/fast_io_hosted/platforms/dos_filename.h
+++ b/include/fast_io_hosted/platforms/dos_filename.h
@@ -29,7 +29,7 @@ inline constexpr bool is_invalid_dos_filename_with_size(char_type const *filenam
 
 	for (; curr != end; ++curr)
 	{
-		if (auto fc{*curr}; ::fast_io::char_category::is_dos_path_invalid_character(fc)) [[unlikely]]
+		if (auto fc{*curr}; ::fast_io::char_category::is_dos_file_invalid_character(fc)) [[unlikely]]
 		{
 			return true;
 		}
diff --git a/include/fast_io_hosted/platforms/posix.h b/include/fast_io_hosted/platforms/posix.h
index cb2f6054..29af7df8 100644
--- a/include/fast_io_hosted/platforms/posix.h
+++ b/include/fast_io_hosted/platforms/posix.h
@@ -271,11 +271,11 @@ inline constexpr int calculate_posix_open_mode(open_mode value) noexcept
 #ifdef _O_SEQUENTIAL
 	if ((value & open_mode::random_access) != open_mode::none)
 	{
-		mode |= _O_SEQUENTIAL;
+		mode |= _O_RANDOM;
 	}
 	else
 	{
-		mode |= _O_RANDOM;
+		mode |= _O_SEQUENTIAL;
 	}
 #endif
 #ifdef O_LARGEFILE
@@ -522,10 +522,36 @@ template <::fast_io::posix_family family, ::std::integral ch_type>
 inline constexpr basic_posix_family_io_observer<family, char>
 io_bytes_stream_ref_define(basic_posix_family_io_observer<family, ch_type> other) noexcept
 {
-	return {other.handle};
+	return {other.fd};
+}
+
+#if defined(__CYGWIN__)
+
+// https://github.com/cygwin/cygwin/blob/c43ec5f5951c7f4b882a0f8e619601a45ae70a91/newlib/libc/include/sys/_default_fcntl.h#L168
+
+inline constexpr posix_at_entry posix_at_fdcwd() noexcept
+{
+	return posix_at_entry(
+#if defined(AT_FDCWD)
+			AT_FDCWD
+#else
+			-2
+#endif
+	);
 }
 
-#if !(defined(_WIN32) && !defined(__WINE__) && !defined(__BIONIC__)) && defined(AT_FDCWD)
+inline constexpr posix_at_entry at_fdcwd() noexcept
+{
+	return posix_at_entry(
+#if defined(AT_FDCWD)
+			AT_FDCWD
+#else
+			-2
+#endif
+	);
+}
+
+#elif !(defined(_WIN32) && !defined(__WINE__) && !defined(__BIONIC__)) && defined(AT_FDCWD)
 
 inline constexpr posix_at_entry posix_at_fdcwd() noexcept
 {
@@ -536,6 +562,7 @@ inline constexpr posix_at_entry at_fdcwd() noexcept
 {
 	return posix_at_entry(AT_FDCWD);
 }
+
 #elif defined(__MSDOS__) || defined(__DJGPP__)
 
 inline constexpr posix_at_entry posix_at_fdcwd() noexcept
@@ -547,6 +574,7 @@ inline constexpr posix_at_entry at_fdcwd() noexcept
 {
 	return posix_at_entry(-100);
 }
+
 #endif
 
 namespace details
@@ -775,7 +803,7 @@ template <::fast_io::posix_family family, ::std::integral ch_type>
 inline auto redirect_handle(basic_posix_family_io_observer<family, ch_type> h) noexcept
 {
 #if (defined(_WIN32) && !defined(__WINE__) && !defined(__BIONIC__))
-	return my_get_osfile_handle(h.fd);
+	return details::my_get_osfile_handle(h.fd);
 #else
 	return h.fd;
 #endif
@@ -892,10 +920,12 @@ inline constexpr my_dos_concat_tlc_path_common_result my_dos_concat_tlc_path_com
 			return {true};
 		}
 
-		if (::fast_io::details::is_invalid_dos_filename_with_size(pathname, sz)) [[unlikely]]
+#if 0
+		if (::fast_io::details::is_invalid_dos_pathname_with_size(pathname, sz)) [[unlikely]]
 		{
 			return {true};
 		}
+#endif
 
 		// concat
 		return {false, concat_dos_path_tlc_string(::fast_io::mnp::os_c_str(fd_pathname_cstr), ::fast_io::mnp::chvw('\\'), ::fast_io::mnp::os_c_str(pathname))};
@@ -921,7 +951,7 @@ inline int my_posix_openat(int dirfd, char const *pathname, int flags, mode_t mo
 	return fd;
 }
 
-#elif defined(__NEWLIB__) || defined(_PICOLIBC__)
+#elif (defined(__NEWLIB__) || defined(_PICOLIBC__)) && !defined(__CYGWIN__)
 
 template <bool always_terminate = false>
 inline int my_posix_openat(int, char const *, int, mode_t)
@@ -980,11 +1010,11 @@ inline constexpr unsigned calculate_win32_cygwin_open_mode(open_mode value)
 	unsigned access{};
 	if ((value & open_mode::out) == open_mode::out)
 	{
-		access |= 0x80000000;
+		access |= 0x40000000 /*GENERIC_WRITE*/;
 	}
 	if ((value & open_mode::in) == open_mode::in)
 	{
-		access |= 0x40000000;
+		access |= 0x80000000 /*GENERIC_READ*/;
 	}
 	return access;
 }
@@ -1052,7 +1082,7 @@ struct my_posix_open_paramter
 	}
 };
 
-#if (defined(__NEWLIB__) && !defined(AT_FDCWD)) || defined(_PICOLIBC__)
+#if ((defined(__NEWLIB__) && !defined(AT_FDCWD)) || defined(_PICOLIBC__)) && !defined(__CYGWIN__)
 
 template <::fast_io::constructible_to_os_c_str T>
 inline constexpr int posix_openat_file_impl(int, T const &, open_mode, perms)
@@ -1528,7 +1558,7 @@ class basic_posix_family_pipe
 		{
 			throw_posix_error();
 		}
-#elif (defined(__MSDOS__) || defined(__DJGPP__)) || defined(__NEWLIB__)
+#elif (defined(__MSDOS__) || defined(__DJGPP__)) || (defined(__NEWLIB__) && !defined(__CYGWIN__))
 		if (noexcept_call(::pipe, a2) == -1)
 		{
 			throw_posix_error();
diff --git a/include/fast_io_hosted/platforms/win32.h b/include/fast_io_hosted/platforms/win32.h
index 5a00c15d..0de1ee0b 100644
--- a/include/fast_io_hosted/platforms/win32.h
+++ b/include/fast_io_hosted/platforms/win32.h
@@ -700,7 +700,7 @@ namespace win32::details
 
 inline ::fast_io::intfpos_t seek_impl(void *handle, ::fast_io::intfpos_t offset, seekdir s)
 {
-#if (_WIN32_WINNT <= 0x0500) || defined(_WIN32_WINDOWS)
+#if (defined(_WIN32_WINNT) && _WIN32_WINNT <= 0x0500) || defined(_WIN32_WINDOWS)
 	if constexpr (sizeof(::fast_io::intfpos_t) > sizeof(::std::int_least32_t))
 	{
 		constexpr ::fast_io::intfpos_t l32mx{INT_LEAST32_MAX};
@@ -781,7 +781,7 @@ inline ::std::byte *win32_read_some_bytes_impl(void *__restrict handle, ::std::b
 }
 
 inline ::std::byte *win32_ntw_pread_some_bytes_impl(void *__restrict handle, ::std::byte *first, ::std::byte *last,
-										  ::fast_io::intfpos_t off)
+													::fast_io::intfpos_t off)
 {
 	// The difference between P-series functions in Windows synchronization mode and POSIX is that under Windows,
 	// the functions will advance the position by the number of bytes written or read after each write/read operation.
@@ -808,13 +808,13 @@ inline ::std::byte const *write_or_pwrite_some_bytes_common_impl(void *__restric
 }
 
 inline ::std::byte const *win32_write_some_bytes_impl(void *__restrict handle, ::std::byte const *first,
-												::std::byte const *last)
+													  ::std::byte const *last)
 {
 	return ::fast_io::win32::details::write_or_pwrite_some_bytes_common_impl(handle, first, last, nullptr);
 }
 
 inline ::std::byte const *win32_ntw_pwrite_some_bytes_impl(void *__restrict handle, ::std::byte const *first,
-												 ::std::byte const *last, ::fast_io::intfpos_t off)
+														   ::std::byte const *last, ::fast_io::intfpos_t off)
 {
 	// The difference between P-series functions in Windows synchronization mode and POSIX is that under Windows,
 	// the functions will advance the position by the number of bytes written or read after each write/read operation.
@@ -853,7 +853,7 @@ inline ::fast_io::intfpos_t io_stream_seek_bytes_define(basic_win32_family_io_ob
 I am not confident that i understand semantics correctly. Disabled first and test it later
 */
 
-// Windows 9x does not support atomic p-series functions. When using operation::p-series functions, 
+// Windows 9x does not support atomic p-series functions. When using operation::p-series functions,
 // they will be emulated through seek and non-p-series functions.
 // For Win9x, use the operation::p series functions, which automatically combine seek operations with non-p series functions.
 #if !defined(_WIN32_WINDOWS)
@@ -1001,7 +1001,7 @@ inline void check_win32_9xa_dir_is_valid(win32_9xa_dir_handle const &h)
 	auto find_struct{::fast_io::win32::FindFirstFileA(reinterpret_cast<char const *>(temp_find_path.c_str()), __builtin_addressof(wfda))};
 	if (find_struct == reinterpret_cast<void *>(static_cast<::std::ptrdiff_t>(-1))) [[unlikely]]
 	{
-		throw_win32_error(0x5);
+		throw_win32_error(0x2);
 	}
 	else
 	{
@@ -1098,10 +1098,12 @@ inline win32_9xa_dir_handle basic_win32_9xa_create_dir_file_at_fs_dirent_impl(wi
 
 	auto const beg{reinterpret_cast<char8_t_const_may_alias_ptr>(filename_c_str)};
 
-	if (::fast_io::details::is_invalid_dos_filename_with_size(beg, filename_c_str_len)) [[unlikely]]
+#if 0
+	if (::fast_io::details::is_invalid_dos_pathname_with_size(beg, filename_c_str_len)) [[unlikely]]
 	{
 		throw_win32_error(3);
 	}
+#endif
 
 	check_win32_9xa_dir_is_valid(*directory_handle);
 	win32_9xa_dir_handle ret{concat_win32_9xa_dir_handle_path_str(directory_handle->path, u8"\\", ::fast_io::mnp::os_c_str_with_known_size(beg, filename_c_str_len))};
@@ -1121,10 +1123,12 @@ inline void *basic_win32_9xa_create_file_at_fs_dirent_impl(win32_9xa_dir_handle
 
 	auto const beg{reinterpret_cast<char8_t_const_may_alias_ptr>(filename_c_str)};
 
-	if (::fast_io::details::is_invalid_dos_filename_with_size(beg, filename_c_str_len)) [[unlikely]]
+#if 0
+	if (::fast_io::details::is_invalid_dos_pathname_with_size(beg, filename_c_str_len)) [[unlikely]]
 	{
 		throw_win32_error(3);
 	}
+#endif
 
 	check_win32_9xa_dir_is_valid(*directory_handle);
 	tlc_win32_9xa_dir_handle_path_str str{concat_tlc_win32_9xa_dir_handle_path_str(directory_handle->path, u8"\\", ::fast_io::mnp::os_c_str_with_known_size(beg, filename_c_str_len))};
@@ -1136,10 +1140,12 @@ inline ::fast_io::win32::details::tlc_win32_9xa_dir_handle_path_str concat_tlc_w
 {
 	auto const beg{path_c_str};
 
-	if (::fast_io::details::is_invalid_dos_filename_with_size(beg, path_size)) [[unlikely]]
+#if 0
+	if (::fast_io::details::is_invalid_dos_pathname_with_size(beg, path_size)) [[unlikely]]
 	{
 		throw_win32_error(3);
 	}
+#endif
 
 	return ::fast_io::win32::details::concat_tlc_win32_9xa_dir_handle_path_str(dirhd.path, u8"\\", ::fast_io::mnp::os_c_str_with_known_size(beg, path_size));
 }
@@ -1745,9 +1751,9 @@ inline posix_file_status win32_9xa_dir_file_status_impl(win32_9xa_dir_handle con
 		tmp_file.perm = static_cast<perms>(pm);
 		tmp_file.type = ::fast_io::file_type::directory;
 		tmp_file.nlink = 1u;
-		tmp_file.size = static_cast<::std::uintmax_t>((static_cast<::std::uint_least64_t>(wfda.nFileSizeHigh) << 32u) | wfda.nFileSizeLow);  // always zero
-		tmp_file.blksize = 512u;  // default
-		tmp_file.blocks = (tmp_file.size + 511u) / 512u;  // default
+		tmp_file.size = static_cast<::std::uintmax_t>((static_cast<::std::uint_least64_t>(wfda.nFileSizeHigh) << 32u) | wfda.nFileSizeLow); // always zero
+		tmp_file.blksize = 512u;                                                                                                            // default
+		tmp_file.blocks = (tmp_file.size + 511u) / 512u;                                                                                    // default
 		tmp_file.atim = to_unix_timestamp(wfda.ftLastAccessTime);
 		tmp_file.mtim = to_unix_timestamp(wfda.ftLastWriteTime);
 		tmp_file.ctim = tmp_file.mtim;
@@ -1781,7 +1787,7 @@ inline posix_file_status win32_9xa_dir_file_status_impl(win32_9xa_dir_handle con
 		{
 			tmp_file.dev = static_cast<::std::uintmax_t>(serial);
 		}
-	
+
 		// get blocksize
 		::std::uint_least32_t sector_per_cluster{};
 		::std::uint_least32_t bytes_per_sector{};
diff --git a/include/fast_io_hosted/platforms/win32_network/win32_9xa_dns.h b/include/fast_io_hosted/platforms/win32_network/win32_9xa_dns.h
index eb8cabb6..ec045698 100644
--- a/include/fast_io_hosted/platforms/win32_network/win32_9xa_dns.h
+++ b/include/fast_io_hosted/platforms/win32_network/win32_9xa_dns.h
@@ -221,7 +221,7 @@ class win32_9xa_dns_file : public win32_9xa_dns_io_observer
 	}
 };
 
-#if (defined(_WIN32_WINDOWS) || _WIN32_WINNT <= 0x0500)
+#if (defined(_WIN32_WINDOWS) || (defined(_WIN32_WINNT) && _WIN32_WINNT <= 0x0500))
 using native_dns_io_observer = win32_9xa_dns_io_observer;
 using native_dns_file = win32_9xa_dns_file;
 using native_dns_iterator = win32_9xa_dns_iterator;
diff --git a/include/fast_io_hosted/process/process/win32.h b/include/fast_io_hosted/process/process/win32.h
index 09cc3a14..719bb96c 100644
--- a/include/fast_io_hosted/process/process/win32.h
+++ b/include/fast_io_hosted/process/process/win32.h
@@ -567,11 +567,13 @@ struct win32_9xa_win9x_create_process_at_fs_dirent
 #endif
 				= char8_t const *;
 
+#if 0
 			auto const beg{reinterpret_cast<char8_t_const_may_alias_ptr>(filename)};
-			if (::fast_io::details::is_invalid_dos_filename_with_size(beg, filename_c_str_len)) [[unlikely]]
+			if (::fast_io::details::is_invalid_dos_pathname_with_size(beg, filename_c_str_len)) [[unlikely]]
 			{
 				throw_win32_error(3);
 			}
+#endif
 
 			// check path handle
 			::fast_io::win32::details::check_win32_9xa_dir_is_valid(*directory_handle);
diff --git a/include/fast_io_hosted/white_hole/white_hole.h b/include/fast_io_hosted/white_hole/white_hole.h
index b431d35c..39923012 100644
--- a/include/fast_io_hosted/white_hole/white_hole.h
+++ b/include/fast_io_hosted/white_hole/white_hole.h
@@ -25,7 +25,7 @@ concept minimum_buffer_input_stream_require_size_impl =
 
 } // namespace fast_io::details
 #if ((defined(__linux__) && defined(__NR_getrandom)) || \
-	 (!defined(__linux__) && __has_include(<sys/random.h>))) && !defined(__wasi__) && !defined(__DARWIN_C_LEVEL)
+	 (!defined(__linux__) && __has_include(<sys/random.h>))) && !defined(__wasi__) && !defined(__DARWIN_C_LEVEL) && !defined(__CYGWIN__)
 #include "linux_getrandom.h"
 #endif
 #if ((defined(__linux__) && defined(__GLIBC__)) || (defined(__BSD_VISIBLE) && !defined(__DARWIN_C_LEVEL))) && 0
@@ -69,7 +69,7 @@ inline int random_entropy(basic_posix_io_observer<ch_type> piob) noexcept
 template <::std::integral char_type>
 using basic_native_white_hole =
 #if defined(_WIN32) && !defined(__WINE__)
-#if defined(_WIN32_WINDOWS) || (_WIN32_WINNT <= 0x0500)
+#if defined(_WIN32_WINDOWS) || (defined(_WIN32_WINNT) && _WIN32_WINNT <= 0x0500)
 	basic_win32_crypt_gen_random_file<char_type>;
 #else
 	basic_rtl_gen_random<char_type>;
@@ -79,7 +79,7 @@ using basic_native_white_hole =
 #elif (((defined(__linux__) && defined(__GLIBC__)) || (defined(__BSD_VISIBLE) && !defined(__DARWIN_C_LEVEL)))) && 0
 	basic_bsd_arc4random<char_type>;
 #elif (defined(__linux__) && defined(__NR_getrandom)) || \
-	(!defined(__linux__) && __has_include(<sys/random.h>)) && !defined(__DARWIN_C_LEVEL)
+	(!defined(__linux__) && __has_include(<sys/random.h>)) && !defined(__DARWIN_C_LEVEL) && !defined(__CYGWIN__)
 	basic_linux_getrandom<char_type>;
 #else
 	basic_posix_dev_urandom<char_type>;