Add a multiplication-based aggregate

accumulator/src/lib.rs

@@ -127,6 +127,63 @@ impl Default for Accumulator {
     }
 }
 
+const VOUT_MAX: usize = 16_000;
+
+/// An alternative accumulator than that of the original SwiftSync write-up, intended to remove the
+/// hashes required to update elements in the set.
+#[derive(Debug)]
+pub struct MultAggregate {
+    memo_table: [[[u8; 16]; 2]; VOUT_MAX],
+    internal: u128,
+}
+
+impl MultAggregate {
+    pub fn new() -> Self {
+        let mut memo_table = [[[0u8; 16]; 2]; VOUT_MAX];
+        for (vout, arr) in memo_table.iter_mut().enumerate() {
+            let bytes = sha256t::hash::<SwiftSyncTag>(&vout.to_le_bytes()).to_byte_array();
+            let (left, right) = split_in_half(bytes);
+            *arr = [left, right];
+        }
+        Self {
+            memo_table,
+            internal: 0,
+        }
+    }
+
+    fn compute_salted_value(&self, outpoint: OutPoint) -> u128 {
+        let branches = self.memo_table[outpoint.vout as usize];
+        let left = branches[0];
+        let right = branches[1];
+        let txid_bytes = outpoint.txid.to_byte_array();
+        let (tx_left, tx_right) = split_in_half(txid_bytes);
+        let lhs = u128::from_le_bytes(left).wrapping_mul(u128::from_le_bytes(tx_left));
+        let rhs = u128::from_le_bytes(right).wrapping_mul(u128::from_le_bytes(tx_right));
+        lhs.wrapping_add(rhs)
+    }
+
+    /// Add an outpoint to the set
+    pub fn add(&mut self, outpoint: OutPoint) {
+        let salted_val = self.compute_salted_value(outpoint);
+        self.internal = self.internal.wrapping_add(salted_val);
+    }
+
+    /// Remove an outpoint from the set
+    pub fn spend(&mut self, outpoint: OutPoint) {
+        let salted_val = self.compute_salted_value(outpoint);
+        self.internal = self.internal.wrapping_sub(salted_val);
+    }
+
+    pub fn is_zero(&self) -> bool {
+        self.internal.eq(&0)
+    }
+}
+
+impl Default for MultAggregate {
+    fn default() -> Self {
+        Self::new()
+    }
+}
 #[cfg(test)]
 mod tests {
     use bitcoin::{
@@ -264,4 +321,25 @@ mod tests {
         acc.update(AccumulatorUpdate::Spent(hash_one));
         assert!(acc.is_zero());
     }
+
+    #[test]
+    fn test_mult_agg_is_zero() {
+        let mut acc = MultAggregate::default();
+        let [outpoint_one, outpoint_two, outpoint_three, outpoint_four, outpoint_five] =
+            make_five_outpoint();
+        // Add the members
+        acc.add(outpoint_one);
+        acc.add(outpoint_two);
+        acc.add(outpoint_five);
+        acc.add(outpoint_four);
+        acc.add(outpoint_three);
+        assert!(!acc.is_zero());
+        // Take away the members
+        acc.spend(outpoint_two);
+        acc.spend(outpoint_five);
+        acc.spend(outpoint_three);
+        acc.spend(outpoint_four);
+        acc.spend(outpoint_one);
+        assert!(acc.is_zero());
+    }
 }

accumulator/tests/test.rs

@@ -1,4 +1,4 @@
-use accumulator::Accumulator;
+use accumulator::{Accumulator, MultAggregate};
 use bitcoin::{OutPoint, Txid};
 use rusqlite::Connection;
 
@@ -29,3 +29,29 @@ fn test_static_utxo_set() {
     }
     assert!(acc.is_zero());
 }
+
+#[test]
+fn test_mult_agg() {
+    let mut acc = MultAggregate::new();
+    let conn = Connection::open("../contrib/data/signet_outpoints.sqlite").unwrap();
+    let mut stmt = conn.prepare(SELECT_STMT).unwrap();
+    let mut rows = stmt.query([]).unwrap();
+    while let Some(row) = rows.next().unwrap() {
+        let txid: String = row.get(0).unwrap();
+        let vout: u32 = row.get(1).unwrap();
+        let txid = txid.parse::<Txid>().unwrap();
+        let outpoint = OutPoint { txid, vout };
+        acc.spend(outpoint);
+    }
+    assert!(!acc.is_zero());
+    let mut stmt = conn.prepare(SELECT_STMT).unwrap();
+    let mut rows = stmt.query([]).unwrap();
+    while let Some(row) = rows.next().unwrap() {
+        let txid: String = row.get(0).unwrap();
+        let vout: u32 = row.get(1).unwrap();
+        let txid = txid.parse::<Txid>().unwrap();
+        let outpoint = OutPoint { txid, vout };
+        acc.add(outpoint);
+    }
+    assert!(acc.is_zero());
+}