bbse — Backward Binary Search Encoding

bbse is a minimal and deterministic encoding scheme for values in a sorted integer range.
It encodes a target value as a binary decision path, following the steps of binary search.

This approach provides a prefix-free, compact, and reversible representation of values
from any [start, end) interval.

✨ Features

• Prefix-free binary encoding for any sorted range
• Customizable midpoint for biased distributions
• Simple, deterministic, and lossless
• Suitable for compression, range indexing, embedded systems
• No heap allocation (except for returned bitvector)

🚀 Example

use bbse::{encode, decode};

let bits = encode(0, 16, 5);        // e.g. [true, false, true]
let value = decode(0, 16, &bits);   // -> 5
assert_eq!(value, 5);

🎯 Custom midpoint

For skewed distributions (e.g., values near the beginning or end), you can control the first midpoint to reduce average path length:

use bbse::{encode_from, decode};

let bits = encode_from(0, 16, 3, 4);  // start=0, end=16, target=3, midpoint=4
let value = decode(0, 16, &bits);
assert_eq!(value, 3);

This gives you greater control over compression performance.

🎨 Use case: color encoding

The algorithm was originally inspired by the need to encode color deltas efficiently in an experimental lossless image format. Each delta channel (R/G/B) was encoded as a binary search path, taking advantage of sorted delta distributions.

This enabled compact per-channel encoding with minimal logic, without relying on entropy coding.

📦 Installation

[dependencies]
bbse = "0.2.0"

📄 License

MIT

🔮 Future directions

• Optional no_std support for embedded targets