fastwrite 0.1.2

// Copyright 2016 Itoa Developers
//
// 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.

use std::{io, ops, ptr};

pub struct Buffer(Vec<u8>);

impl Buffer {
    #[inline]
    pub fn new() -> Self {
        Buffer(Vec::new())
    }

    #[inline]
    pub fn with_capacity(capacity: usize) -> Self {
        Buffer(Vec::with_capacity(capacity))
    }

    #[inline]
    pub fn into_bytes(self) -> Vec<u8> {
        self.0
    }
}

impl ops::Deref for Buffer {
    type Target = Vec<u8>;

    #[inline]
    fn deref(&self) -> &Vec<u8> {
        &self.0
    }
}

impl ops::DerefMut for Buffer {
    #[inline]
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

impl io::Write for Buffer {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        extend_from_slice(&mut self.0, buf);
        Ok(buf.len())
    }

    #[inline]
    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
        extend_from_slice(&mut self.0, buf);
        Ok(())
    }

    #[inline]
    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}

// LLVM is not able to lower `Vec::extend_from_slice` into a memcpy, so this
// helps eke out that last bit of performance.
#[inline]
fn extend_from_slice(dst: &mut Vec<u8>, src: &[u8]) {
    let dst_len = dst.len();
    let src_len = src.len();

    dst.reserve(src_len);

    unsafe {
        // We would have failed if `reserve` overflowed
        dst.set_len(dst_len + src_len);

        ptr::copy_nonoverlapping(
            src.as_ptr(),
            dst.as_mut_ptr().offset(dst_len as isize),
            src_len);
    }
}