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    // Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.
    //
    // Original authors: alexchrichton, bluss

    // UTF-8 ranges and tags for encoding characters
    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;

    /// Placeholder
    pub struct EncodeUtf8Error;

    /// Encode a char into buf using UTF-8.
    ///
    /// On success, return the byte length of the encoding (1, 2, 3 or 4).<br>
    /// On error, return `EncodeUtf8Error` if the buffer was too short for the char.
    #[inline]
    pub fn encode_utf8(ch: char, buf: &mut [u8]) -> Result<usize, EncodeUtf8Error>
    {
        let code = ch as u32;
        if code < MAX_ONE_B && buf.len() >= 1 {
            buf[0] = code as u8;
            return Ok(1);
        } else if code < MAX_TWO_B && buf.len() >= 2 {
            buf[0] = (code >> 6 & 0x1F) as u8 | TAG_TWO_B;
            buf[1] = (code & 0x3F) as u8 | TAG_CONT;
            return Ok(2);
        } else if code < MAX_THREE_B && buf.len() >= 3 {
            buf[0] = (code >> 12 & 0x0F) as u8 | TAG_THREE_B;
            buf[1] = (code >>  6 & 0x3F) as u8 | TAG_CONT;
            buf[2] = (code & 0x3F) as u8 | TAG_CONT;
            return Ok(3);
        } else if buf.len() >= 4 {
            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;
            return Ok(4);
        };
        Err(EncodeUtf8Error)
    }

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