allsorts_no_std 0.5.3

no_std fork of allsorts (OpenType/WOFF/WOFF2 font parser, shaping engine, subsetter). Fork of YesLogic's allsorts — please file issues at github.com/fschutt/allsorts-azul, NOT the upstream YesLogic repo.
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//! Big5 encoding.

use encoding_rs::{EncoderResult, BIG5};

pub fn unicode_to_big5(u: char) -> Option<u16> {
    let mut encoder = BIG5.new_encoder();
    let src: &mut [u8] = &mut [0, 0, 0, 0];
    let mut dst = [0, 0];
    let (res, _read, written) =
        encoder.encode_from_utf8_without_replacement(u.encode_utf8(src), &mut dst, true);
    match res {
        EncoderResult::InputEmpty => {
            match written {
                1 => Some(u16::from(dst[0])),
                2 => Some(u16::from_be_bytes(dst)),
                _ => None, // should not happen
            }
        }
        EncoderResult::OutputFull => None, // should not happen
        EncoderResult::Unmappable(_) => None,
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn ascii_to_big5() {
        for i in 0..128 {
            let u = char::from(i);
            assert_eq!(unicode_to_big5(u), Some(u16::from(i)));
        }
    }

    #[test]
    fn chinese_to_big5() {
        assert_eq!(unicode_to_big5('好'), Some(0xA66E));
    }

    #[test]
    fn greek_to_big5() {
        assert_eq!(unicode_to_big5('ε'), Some(0xA360));
    }

    #[test]
    fn hindi_to_big5() {
        assert_eq!(unicode_to_big5('म'), None);
    }
}