Varuint

Variable length signed and unsigned integer types. Types support up to 64-bit integers (128-bit integers support will be added when Rust has the i128 and u128 types).

Encoding rules are based on SQLite 4 Varuint type with modifications for future support of 128-bit long integers. Varint is encoded using the Protobuf ZigZag approach and reuses Varuint as a storage.

Unlike the Protobuf encoding rules, Varuint needs the first byte only to find out the length of the whole value. Microbenchmarks say that it is a lot faster.

See crate docs for more details.

How to use

Add dependency to Cargo.toml:

[dependencies]
varuint = "0.1"

Update you project:

extern crate varuint;

use std::mem;

use varuint::{Varuint, VarType};
use std::io::Read;


fn test_varuint(v: u64, size: usize) {
    let v = Varuint(v);
    assert_eq!(size, v.size_hint());
    let mut arr: [u8; 9] = unsafe { mem::uninitialized() };
    {
        let mut buf = &mut arr as &mut [u8];
        assert_eq!(size, v.write(&mut buf).unwrap());
    }
    let mut buf: &[u8] = &arr;
    let mut read: &mut Read = &mut buf;
    assert_eq!(v, Varuint::read(read).unwrap());
}

fn main() {
    test_varuint(0, 1);
    test_varuint(240, 1);

    test_varuint(241, 2);
    test_varuint(2031, 2);

    test_varuint(2032, 3);
    test_varuint(67567, 3);

    test_varuint(67568, 4);
    test_varuint(16777215, 4);

    test_varuint(16777216, 5);
    test_varuint(4294967295, 5);

    test_varuint(4294967296, 6);
    test_varuint(1099511627775, 6);

    test_varuint(1099511627776, 7);
    test_varuint(281474976710655, 7);

    test_varuint(281474976710656, 8);
    test_varuint(72057594037927935, 8);

    test_varuint(72057594037927936, 9);
    test_varuint(u64::max_value(), 9);
}