SwiftSync Hintsfile

SwiftSync is a protocol to accelerate the initial block download for Bitcoin clients. The protocol requires hints as to what coins will remain unspent at a particular block height throughout the chain history. This crate is an implementation of a file that encodes such hints. In essence, it is an concise encoding of the UTXO set.

Methodology

The file encodes monotonically increasing indices within a block for which coins remain unspent. Given a block of M elements, suppose N are not spent, then the file encodes these positions with $2n + n \lceil \log_2(m/n) \rceil$ bits. This is near the optimum of $\log_2 \binom{m}{n}$

The technique used for this encoding was developed by Elias and Fano, which you may read about here.

Usage

cargo add hintsfile

use hintsfile::Hintsfile;

// Load a file
let hints = Hintsfile::from_reader(&mut file)?;

MSRV

This crate compiles with a toolchain of 1.80.0 or higher.