Unicode(unicode scalar) to UTF-16

What is a unicode scalar?

https://www.quora.com/What-is-a-unicode-scalar

为什么 U+12345 -> D808 DF45(utf16) ？

Table : UTF-16 Bit Distribution

Scalar ValueUTF-16xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx000uuuuuxxxxxxxxxxxxxxxx110110wwwwxxxxxx 110111xxxxxxxxxx

Note: wwww = uuuuu - 1

ref: https://www.unicode.org/versions/Unicode13.0.0/ch03.pdf#G7404 Unicode 术语： https://www.unicode.org/glossary/#unicode_scalar_value