74 lines
2.7 KiB
Rust
74 lines
2.7 KiB
Rust
//! The `ledger` crate provides the foundational data structures for Proof-of-History,
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//! an ordered log of events in time.
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/// Each entry contains three pieces of data. The 'num_hashes' field is the number
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/// of hashes performed since the previous entry. The 'id' field is the result
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/// of hashing 'id' from the previous entry 'num_hashes' times. The 'event'
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/// field points to an Event that took place shortly after 'id' was generated.
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///
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/// If you divide 'num_hashes' by the amount of time it takes to generate a new hash, you
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/// get a duration estimate since the last event. Since processing power increases
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/// over time, one should expect the duration 'num_hashes' represents to decrease proportionally.
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/// Though processing power varies across nodes, the network gives priority to the
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/// fastest processor. Duration should therefore be estimated by assuming that the hash
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/// was generated by the fastest processor at the time the entry was recorded.
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use hash::Hash;
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use entry::{next_tick, Entry};
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use rayon::prelude::*;
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/// Verifies the hashes and counts of a slice of events are all consistent.
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pub fn verify_slice(entries: &[Entry], start_hash: &Hash) -> bool {
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let genesis = [Entry::new_tick(Default::default(), start_hash)];
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let event_pairs = genesis.par_iter().chain(entries).zip(entries);
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event_pairs.all(|(x0, x1)| x1.verify(&x0.id))
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}
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/// Create a vector of Ticks of length 'len' from 'start_hash' hash and 'num_hashes'.
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pub fn next_ticks(start_hash: &Hash, num_hashes: u64, len: usize) -> Vec<Entry> {
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let mut id = *start_hash;
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let mut ticks = vec![];
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for _ in 0..len {
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let entry = next_tick(&id, num_hashes);
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id = entry.id;
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ticks.push(entry);
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}
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ticks
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use hash::hash;
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#[test]
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fn test_verify_slice() {
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let zero = Hash::default();
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let one = hash(&zero);
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assert!(verify_slice(&vec![], &zero)); // base case
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assert!(verify_slice(&vec![Entry::new_tick(0, &zero)], &zero)); // singleton case 1
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assert!(!verify_slice(&vec![Entry::new_tick(0, &zero)], &one)); // singleton case 2, bad
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assert!(verify_slice(&next_ticks(&zero, 0, 2), &zero)); // inductive step
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let mut bad_ticks = next_ticks(&zero, 0, 2);
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bad_ticks[1].id = one;
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assert!(!verify_slice(&bad_ticks, &zero)); // inductive step, bad
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}
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}
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#[cfg(all(feature = "unstable", test))]
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mod bench {
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extern crate test;
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use self::test::Bencher;
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use ledger::*;
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#[bench]
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fn event_bench(bencher: &mut Bencher) {
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let start_hash = Default::default();
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let events = next_ticks(&start_hash, 10_000, 8);
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bencher.iter(|| {
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assert!(verify_slice(&events, &start_hash));
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});
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}
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}
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