fastvlq

A fast variant of variable-length quantity encoding with a focus on speed and no_std support.

The algorithm uses leading zeros in the first byte to determine how many bytes are required for decoding, allowing the length to be known immediately without parsing the entire value.

Supported Types

Type	Max Bytes
Vu32	5
Vi32	5
Vu64	9
Vi64	9
Vu128	18
Vi128	18

Signed types (Vi*) use zigzag encoding for efficient storage of small absolute values.

Vu64 Compression

Bytes	Min	Max
1	0	127 (0x7F)
2	128 (0x80)	16,511 (0x407F)
3	16,512 (0x4080)	2,113,663 (0x20407F)
4	2,113,664 (0x204080)	270,549,119 (0x1020407F)
5	270,549,120 (0x10204080)	34,630,287,487 (0x81020407F)
6	34,630,287,488 (0x810204080)	4,432,676,798,591 (0x4081020407F)
7	4,432,676,798,592 (0x40810204080)	567,382,630,219,903 (0x204081020407F)
8	567,382,630,219,904 (0x2040810204080)	72,624,976,668,147,839 (0x10204081020407F)
9	72,624,976,668,147,840 (0x102040810204080)	18,446,744,073,709,551,615 (0xFFFFFFFFFFFFFFFF)

Usage

Add this to your Cargo.toml:

[dependencies]
fastvlq = "2"

Features

• std (default) - Enables Read/Write extension traits
• async-futures - Enables async extension traits via futures-io
• async-tokio - Enables async extension traits via tokio

Where is this used?

• box - a modern replacement for the zip file format

License

Licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.