LibC: Add some missing wchar.h functions

isw* functions are just wrappers to is*
tow* functions are just wrappers to to*

userspace/libraries/LibC/wchar-stdio.cpp

@@ -0,0 +1,102 @@
+#include <BAN/UTF8.h>
+
+#include <errno.h>
+#include <wchar.h>
+
+struct FILEScopeLock
+{
+	FILEScopeLock(FILE* stream)
+		: m_stream(stream)
+	{
+		flockfile(m_stream);
+	}
+	~FILEScopeLock()
+	{
+		funlockfile(m_stream);
+	}
+	FILE* m_stream;
+};
+
+wint_t getwc(FILE* stream)
+{
+	return fgetwc(stream);
+}
+
+wint_t fgetwc(FILE* stream)
+{
+	FILEScopeLock _(stream);
+
+	char buffer[4];
+
+	buffer[0] = getc_unlocked(stream);
+	if (buffer[0] == EOF)
+		return WEOF;
+
+	const auto length = BAN::UTF8::byte_length(buffer[0]);
+	if (length == BAN::UTF8::invalid)
+	{
+		errno = EILSEQ;
+		return WEOF;
+	}
+
+	for (uint32_t i = 1; i < length; i++)
+		if ((buffer[i] = getc_unlocked(stream)) == EOF)
+			return WEOF;
+
+	const auto ret = BAN::UTF8::to_codepoint(buffer);
+	if (ret == BAN::UTF8::invalid)
+	{
+		errno = EILSEQ;
+		return WEOF;
+	}
+
+	return ret;
+}
+
+wint_t putwc(wchar_t wc, FILE* stream)
+{
+	return fputwc(wc, stream);
+}
+
+wint_t fputwc(wchar_t wc, FILE* stream)
+{
+	char buffer[4];
+	if (!BAN::UTF8::from_codepoints(&wc, 1, buffer))
+	{
+		errno = EILSEQ;
+		return WEOF;
+	}
+
+	FILEScopeLock _(stream);
+
+	const auto bytes = BAN::UTF8::byte_length(buffer[0]);
+	for (uint32_t i = 0; i < bytes; i++)
+		if (putc_unlocked(buffer[i], stream) == EOF)
+			return WEOF;
+
+	return wc;
+}
+
+wint_t ungetwc(wint_t wc, FILE* stream)
+{
+	char buffer[4];
+	if (!BAN::UTF8::from_codepoints(&wc, 1, buffer))
+	{
+		errno = EILSEQ;
+		return WEOF;
+	}
+
+	FILEScopeLock _(stream);
+
+	const auto bytes = BAN::UTF8::byte_length(buffer[0]);
+	for (uint32_t i = 0; i < bytes; i++)
+	{
+		if (ungetc(buffer[i], stream) != EOF)
+			continue;
+		for (uint32_t j = 0; j < i; j++)
+			fgetc(stream);
+		return WEOF;
+	}
+
+	return wc;
+}