UTF-8 to Shift_JIS in C

Hello /prog/,

Since most of you are EXPERT C-PROGRAMMERS I thought some of you might have an idea as how to best implement this.
In short, I need to convert (wchar_t) UTF-8 input to Shift_JIS, but I am a very incompetent C programmer.

My current implementation is to convert the entire map located here: http://unicode.org/Public/MAPPINGS/OBSOLETE/EASTASIA/JIS/SHIFTJIS.TXT to a huge string on the form ("u%s%s", unicode, sjiscode) and then searching for the hexform of the unicode input.
This is obviously very slow and I ask of you if you could be so kind as to tell me how one is supposed to go about doing this sort of thing in C, as I currently am in a learning process.

Thank you for your attention.

>>1
Protip: wchar_t is never 'encoded' in UTF-8. In fact, you'd have to be fucking retarded to waste up to three bytes for each character. I believe you have no idea what Unicode is about.