LibC: Implement wcrtomb

This function converts a single wide character into its multibyte
representation (UTF-8 in our case). It is called from libc++'s
`std::basic_ostream<wchar_t>::flush`, which gets called at program exit
from a global destructor in order to flush `std::wcout`.

1 files changed, 25 insertions, 0 deletions

diff --git a/AK/UnicodeUtils.h b/AK/UnicodeUtils.h
index e7211deaea..18ce9a7daa 100644
--- a/AK/UnicodeUtils.h
+++ b/AK/UnicodeUtils.h
@@ -17,4 +17,29 @@ constexpr bool is_unicode_control_code_point(u32 code_point)
 
 Optional<StringView> get_unicode_control_code_point_alias(u32);
 
+template<typename Callback>
+[[nodiscard]] constexpr int code_point_to_utf8(u32 code_point, Callback callback)
+{
+    if (code_point <= 0x7f) {
+        callback((char)code_point);
+        return 1;
+    } else if (code_point <= 0x07ff) {
+        callback((char)(((code_point >> 6) & 0x1f) | 0xc0));
+        callback((char)(((code_point >> 0) & 0x3f) | 0x80));
+        return 2;
+    } else if (code_point <= 0xffff) {
+        callback((char)(((code_point >> 12) & 0x0f) | 0xe0));
+        callback((char)(((code_point >> 6) & 0x3f) | 0x80));
+        callback((char)(((code_point >> 0) & 0x3f) | 0x80));
+        return 3;
+    } else if (code_point <= 0x10ffff) {
+        callback((char)(((code_point >> 18) & 0x07) | 0xf0));
+        callback((char)(((code_point >> 12) & 0x3f) | 0x80));
+        callback((char)(((code_point >> 6) & 0x3f) | 0x80));
+        callback((char)(((code_point >> 0) & 0x3f) | 0x80));
+        return 4;
+    }
+    return -1;
+}
+
 }