Crate varuint

Variable length signed and unsigned integer types. Types support up to 128-bit integers, both are encoded to 1-17 bytes.

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

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

How to use

Add dependency to your Cargo.toml:

[dependencies]
varuint = "0.6"

Add imports to your code:

use varuint::{Varint, Serializable, Deserializable};

Use it:

use std::mem;
use std::io::Cursor;

use varuint::*;

fn main() {
    let mut cursor = Cursor::new(vec![]);
    let _ = cursor.write_varint(1u8).unwrap();
    let _ = cursor.write_varint(-300i16).unwrap();
    let v = Varint(-56_782i128);
    let _ = v.serialize(&mut cursor).unwrap();
    cursor.set_position(0);
    assert_eq!(1u8, ReadVarint::<u8>::read_varint(&mut cursor).unwrap());
    assert_eq!(-300i16, ReadVarint::<i16>::read_varint(&mut cursor).unwrap());
    assert_eq!(v, Varint::<i128>::deserialize(&mut cursor).unwrap());
}

Encoding rules

Encoding rules for unsinged integer Varint are (assuming value is V):

• If V<=240 then output a single byte A0 equal to V.
• If V<=2031 then output A0 as (V-240)/256 + 241 and A1 as (V-240)%256.
• If V<=67567 then output A0 as 248, A1 as (V-2032)/256, and A2 as (V-2032)%256.
• If V<=16_777_215 then output A0 as 249 and A1 through A3 as a little-endian 3-byte integer.
• If V<=4_294_967_295 then output A0 as 250 and A1..A4 as a little-endian 4-byte integer.
• If V<=1_099_511_627_775 then output A0 as 251 and A1..A5 as a little-endian 5-byte integer.
• If V<=281_474_976_710_655 then output A0 as 252 and A1..A6 as a little-endian 6-byte integer.
• If V<=72_057_594_037_927_935 then output A0 as 253 and A1..A7 as a little-endian 7-byte integer.
• If V<=9_223_372_036_854_775_807 then output A0 as 254 and A1..A8 as a little-endian 8-byte integer.
• Otherwise output A0 as 255 and A1..A16 as a little-endian 16-byte integer.

Signed integer Varint converted to the unsigned integer Varint in the first place and then encoded as an unsigned integer. Conversion method makes values closer to 0 to take less space. See Protobuf docs for details.

Structs

Varint

Variable length signed integer.

Traits

Deserializable	Trait for deserializable types
ReadVarint
Serializable	Trait for serializable types
VarintBaseType
VarintSizeHint	Varuint size hinting trait
WriteVarint