[][src]Crate vint64

vint64: simple and efficient variable-length integer encoding

About

This crate implements a variable-length encoding for 64-bit little endian integers with a number of properties which make it superior in every way to other variable-length integer encodings like LEB128, SQLite "Varuints" or CBOR:

  • Capable of expressing the full 64-bit integer range with a maximum of 9-bytes
  • No loops involved in decoding: just (unaligned) loads, masks, and shifts
  • No complex branch-heavy logic - decoding is CTZ + shifts and sanity checks
  • Total length of a vint64 can be determined via the first byte alone

Some precedent for this sort of encoding can be found in the Extensible Binary Meta Language (used by e.g. the Matroska media container format), however note that the specific type of "vint" used by this format still requires a loop to decode.

Usage

// Encode a 64-bit integer as a vint64
let encoded = vint64::encode(42);
assert_eq!(encoded.as_ref(), &[0x55]);

// Decode an encoded vint64 with trailing data
let mut slice: &[u8] = &[0x55, 0xde, 0xad, 0xbe, 0xef];
let decoded = vint64::decode(&mut slice).unwrap();
assert_eq!(decoded, 42);
assert_eq!(slice, &[0xde, 0xad, 0xbe, 0xef]);

// Zigzag encoding can be used to encode signed vint64s.
// Decode with `vint64::decode_signed`.
let signed = vint64::encode_signed(-42);
assert_eq!(signed.as_ref(), &[0xa7]);

Structs

Error

Error type: indicates decoding failure

Vint64

vint64: serialized variable-width 64-bit integers

Constants

MAX_BYTES

Maximum length of a vint64 in bytes

Functions

decode

Decode a vint64-encoded unsigned 64-bit integer.

decode_signed

Decode a zigzag-encoded vint64 as a signed integer

encode

Encode an unsigned 64-bit integer as vint64

encode_signed

Encode a signed integer as a zigzag-encoded vint64

length_hint

Get the length of a vint64 from the first byte