k-nucleotide Rust #2 program

// The Computer Language Benchmarks Game
// https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
//
// contributed by Mrjillhace

extern crate fnv;

use std::thread;
use std::sync::Arc;
use std::collections::HashMap;
use std::hash::BuildHasherDefault;
use fnv::FnvHasher;

const SEQ_LENS: [usize; 7] = [1, 2, 3, 4, 6, 12, 18];
const LOOKUPS: [&'static str; 5] = ["GGT", "GGTA", "GGTATT", "GGTATTTTAATT", "GGTATTTTAATTTATAGT"];

type Table = HashMap<u64, usize, BuildHasherDefault<FnvHasher>>;

fn encode(c: char) -> u8 {
    match c {
        'a' | 'A' => 0,
        'c' | 'C' => 1,
        'g' | 'G' => 2,
        't' | 'T' => 3,
        _ => panic!("wrong character"),
    }
}

fn encode_str(s: &str) -> u64 {
    s.chars().fold(0, |acc, c| 4 * acc + encode(c) as u64)
}

//require char length to decode, otherwise "AC" == "C"
fn decode(mut v: u64, len: usize) -> String {
    let mut s = String::new();
    for _ in 0..len {
        let digit = v % 4;
        match digit {
            0 => s.push('A'),
            1 => s.push('C'),
            2 => s.push('G'),
            3 => s.push('T'),
            _ => {}
        };
        v /= 4;
    }
    s.chars().rev().collect()
}

struct Buffer{
    value: u64,
    size: usize,
}

impl Buffer {
    fn push(&mut self, c: u8) {
        self.value = (self.value * (1 << 2)) % (1 << (2 * self.size)) + (c as u64);
    }
}

fn parse(mut input: &[u8], len: usize) -> Table {
    let fnv = BuildHasherDefault::<FnvHasher>::default();
    let mut table = Table::with_hasher(fnv);
    let mut buffer = Buffer{ value: 0, size: len };
    if input.len() < len { return table; }
    for _ in 0..len - 1 {
        buffer.push(input[0]);
        input = &input[1..];
    }
    while input.len() != 0 {
        buffer.push(input[0]);
        input = &input[1..];
        let counter = table.entry(buffer.value).or_insert(0);
        *counter += 1;
    }
    table
}

fn read_input<R: std::io::BufRead>(source: R, key: &str) -> Vec<u8> {
    let mut vec = Vec::new();
    for l in source.lines().map(|l| l.ok().unwrap())
        .skip_while(|l| key != &l[..key.len()]).skip(1)
    {
        vec.extend(l.trim().chars().map(|b| encode(b)));
    }
    vec
}

fn report(table: &(usize, Table)) {
    let mut vec = Vec::new();
    let len = table.0;

    for entry in table.1.iter() {
        vec.push((decode(*entry.0, len), *entry.1));
    }
    vec.sort_by(|a, b| b.1.cmp(&a.1));
    let sum = vec.iter().fold(0, |acc, i| acc + i.1);
    for seq in vec {
        println!("{} {:.3}", seq.0, (seq.1 * 100) as f32 / sum as f32);
    }
    println!("");
}

fn main() {
    let stdin = std::io::stdin();
    let input: Vec<u8> = read_input(stdin.lock(), ">THREE");
    let input = Arc::new(input);
    //separate hashmap for each sequence length
    let tables_handle: Vec<_> = SEQ_LENS.iter().map(|&i| {
        let input = input.clone();
        (i, thread::spawn(move || parse(&input, i)))
    }).collect();

    let mut tables = Vec::new();
    for (i, handle) in tables_handle {
        tables.push((i, handle.join().unwrap()));
    }


    report(&tables[0]);
    report(&tables[1]);
    for &seq in &LOOKUPS {
        let index = SEQ_LENS.iter().position(|&x| x == seq.len()).unwrap();
        let num = encode_str(seq);
        println!("{}\t{}",tables[index].1.get(&num).unwrap_or(&0), seq);
    }
}
    

NOTES:
64-bit Ubuntu quad core
rustc 1.44.0 (49cae5576 2020-06-01)
LLVM version: 9.0


Fri, 05 Jun 2020 20:26:45 GMT

MAKE:
/opt/src/rust-1.44.0/bin/rustc -C opt-level=3 -C target-cpu=core2 -C lto -C codegen-units=1 -L /opt/src/rust-libs --extern futures=/opt/src/rust-libs/libfutures-ad0a024e469c2676.rlib --extern indexmap=/opt/src/rust-libs/libindexmap-2c478dbb2ab92df4.rlib knucleotide.rs -o knucleotide.rust-2.rust_run

17.24s to complete and log all make actions

COMMAND LINE:
./knucleotide.rust-2.rust_run 0 < knucleotide-input25000000.txt

PROGRAM OUTPUT:
A 30.295
T 30.151
C 19.800
G 19.754

AA 9.177
TA 9.132
AT 9.131
TT 9.091
CA 6.002
AC 6.001
AG 5.987
GA 5.984
CT 5.971
TC 5.971
GT 5.957
TG 5.956
CC 3.917
GC 3.911
CG 3.909
GG 3.902

1471758	GGT
446535	GGTA
47336	GGTATT
893	GGTATTTTAATT
893	GGTATTTTAATTTATAGT