sort-TXT-RUST3

use std::{fs::OpenOptions, fs::File, time::Instant, path::Path};
use memmap2::Mmap;
use memmap2::MmapMut;

pub fn spease_one(input: impl AsRef<Path>, output: impl AsRef<Path>) -> std::io::Result<()> {
    let (chars_to_write, total_len) = {
        let f = File::open(input)?;
        let fm = unsafe { Mmap::map(&f) }?;
        #[cfg(unix)]
        fm.advise(Advice::Sequential)?;

        let mut char_counter = [0u64; 256];
        for c in fm.as_ref() {
            *unsafe { char_counter.get_unchecked_mut(*c as usize) } += 1;
        }

        (char_counter, fm.len())
    };

    let of = OpenOptions::new().read(true).write(true).create(true).open(output)?;
    of.set_len(total_len as u64)?;
    let mut ofm = unsafe { MmapMut::map_mut(&of) }?;
    let mut writer = ofm.as_mut();
    for (c,v) in chars_to_write.into_iter().enumerate().map(|(c,v)| (c as u8, v as usize)) {
        if c != b' ' {
            let (begin, end) = writer.split_at_mut(v);
            begin.fill(c);
            writer = end;
        }
    }

    writer.fill(b' ');

    Ok(())
}
fn main() {
    let start = Instant::now();
    spease_one("input.txt", "output").unwrap();
    println!("Rust Time {:?}", start.elapsed());
}