vendor/serde/src/de/utf8.rs

use lib::*;

const TAG_CONT: u8 = 0b1000_0000;
const TAG_TWO_B: u8 = 0b1100_0000;
const TAG_THREE_B: u8 = 0b1110_0000;
const TAG_FOUR_B: u8 = 0b1111_0000;
const MAX_ONE_B: u32 = 0x80;
const MAX_TWO_B: u32 = 0x800;
const MAX_THREE_B: u32 = 0x10000;

#[inline]
pub fn encode(c: char) -> Encode {
    let code = c as u32;
    let mut buf = [0; 4];
    let pos = if code < MAX_ONE_B {
        buf[3] = code as u8;
        3
    } else if code < MAX_TWO_B {
        buf[2] = (code >> 6 & 0x1F) as u8 | TAG_TWO_B;
        buf[3] = (code & 0x3F) as u8 | TAG_CONT;
        2
    } else if code < MAX_THREE_B {
        buf[1] = (code >> 12 & 0x0F) as u8 | TAG_THREE_B;
        buf[2] = (code >> 6 & 0x3F) as u8 | TAG_CONT;
        buf[3] = (code & 0x3F) as u8 | TAG_CONT;
        1
    } else {
        buf[0] = (code >> 18 & 0x07) as u8 | TAG_FOUR_B;
        buf[1] = (code >> 12 & 0x3F) as u8 | TAG_CONT;
        buf[2] = (code >> 6 & 0x3F) as u8 | TAG_CONT;
        buf[3] = (code & 0x3F) as u8 | TAG_CONT;
        0
    };
    Encode { buf, pos }
}

pub struct Encode {
    buf: [u8; 4],
    pos: usize,
}

impl Encode {
    pub fn as_str(&self) -> &str {
        str::from_utf8(&self.buf[self.pos..]).unwrap()
    }
}