simdnbt

Simdnbt is a very fast NBT serializer and deserializer.

It was originally made as a joke but it ended up being too good of a joke so it's actually a thing now.

Usage

cargo add simdnbt

Deserializing

For deserializing, you'll likely want either simdnbt::borrow::read or simdnbt::owned::read. The difference is that the "borrow" variant requires you to keep a reference to the original buffer, but is significantly faster.

use std::borrow::Cow;
use std::io::Cursor;

fn example(item_bytes: &[u8]) {
    let nbt = simdnbt::borrow::read(&mut Cursor::new(item_bytes))
        .unwrap()
        .unwrap();
    let skyblock_id: Cow<str> = nbt
        .list("i")
        .and_then(|i| i.compounds())
        .and_then(|i| i.first())
        .and_then(|i| i.compound("tag"))
        .and_then(|tag| tag.compound("ExtraAttributes"))
        .and_then(|ea| ea.string("id"))
        .map(|id| id.to_string_lossy())
        .unwrap_or_default();
}

Serializing

use simdnbt::owned::{BaseNbt, Nbt, NbtCompound, NbtTag};

let nbt = Nbt::Some(BaseNbt::new(
    "",
    NbtCompound::from_values(vec![
        ("key".into(), NbtTag::String("value".into())),
    ]),
));
let mut buffer = Vec::new();
nbt.write(&mut buffer);

Performance guide

Use the borrow variant of Nbt if possible, and avoid allocating unnecessarily (for example, keep strings as Cow<str> if you can).

If you're using the owned variant of simdnbt, switching to a faster allocator like mimalloc may help a decent amount (it's ~20% faster on my machine). Setting RUSTFLAGS='-C target-cpu=native' when running your code may also help a little bit.

Implementation details

Simdnbt currently makes use of SIMD instructions for two things:

• swapping the endianness of int arrays
• checking if a string is plain ascii for faster MUTF-8 to UTF-8 conversion

Simdnbt cheats takes some shortcuts to be this fast:

1. it requires a reference to the original data (to avoid cloning)
2. it doesn't validate/decode the MUTF-8 strings at decode-time

Several ideas are borrowed from simdjson, notably the usage of a tape.

Benchmarks

Simdnbt is the fastest NBT parser in Rust.

Here's a benchmark comparing Simdnbt against a few of the other fastest NBT crates for decoding complex_player.dat:

Library	Throughput
simdnbt::borrow	3.9493 GiB/s
simdnbt::owned	825.59 MiB/s
shen_nbt5	606.68 MiB/s
graphite_binary	363.94 MiB/s
azalea_nbt	330.46 MiB/s
valence_nbt	279.58 MiB/s
hematite_nbt	180.22 MiB/s
fastnbt	162.92 MiB/s

And for writing complex_player.dat:

Library	Throughput
simdnbt::owned	2.5033 GiB/s
azalea_nbt	2.4152 GiB/s
simdnbt::borrow	2.1317 GiB/s
graphite_binary	1.8804 GiB/s

The tables above were made from the compare benchmark in this repo. Note that the benchmark is somewhat unfair, since simdnbt::borrow doesn't fully decode some things like strings and integer arrays until they're used. Also keep in mind that if you run your own benchmark you'll get different numbers, but the speeds should be about the same relative to each other.