remove prev_id, unused (#2150)

src/entry.rs

@@ -32,9 +32,6 @@ pub type EntryReceiver = Receiver<Vec<Entry>>;
 
 #[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
 pub struct Entry {
-    /// The the previous Entry ID.
-    pub prev_id: Hash,
-
     /// tick height of the ledger, not including any tick implied by this Entry
     pub tick_height: u64,
 
@@ -61,7 +58,6 @@ impl Entry {
         let entry = {
             if num_hashes == 0 && transactions.is_empty() {
                 Entry {
-                    prev_id: *prev_id,
                     tick_height,
                     num_hashes: 0,
                     id: *prev_id,
@@ -72,7 +68,6 @@ impl Entry {
                 // next_hash will generate the next hash and set num_hashes == 1
                 let id = next_hash(prev_id, 1, &transactions);
                 Entry {
-                    prev_id: *prev_id,
                     tick_height,
                     num_hashes: 1,
                     id,
@@ -84,7 +79,6 @@ impl Entry {
                 // and transactions = empty
                 let id = next_hash(prev_id, num_hashes, &transactions);
                 Entry {
-                    prev_id: *prev_id,
                     tick_height,
                     num_hashes,
                     id,
@@ -122,9 +116,9 @@ impl Entry {
     pub fn serialized_size(transactions: &[Transaction]) -> u64 {
         let txs_size = serialized_size(transactions).unwrap();
 
-        // tick_height+num_hashes    +     id+prev_id  +        txs
+        // tick_height+num_hashes   +    id  +              txs
 
-        (2 * size_of::<u64>() + 2 * size_of::<Hash>()) as u64 + txs_size
+        (2 * size_of::<u64>() + size_of::<Hash>()) as u64 + txs_size
     }
 
     pub fn num_will_fit(transactions: &[Transaction]) -> usize {
@@ -180,21 +174,15 @@ impl Entry {
     /// since the previous transaction and that resulting `id`.
 
     #[cfg(test)]
-    pub fn new_tick(prev_id: &Hash, tick_height: u64, num_hashes: u64, id: &Hash) -> Self {
+    pub fn new_tick(tick_height: u64, num_hashes: u64, id: &Hash) -> Self {
         Entry {
-            prev_id: *prev_id,
             tick_height,
-
             num_hashes,
             id: *id,
             transactions: vec![],
         }
     }
 
-    pub fn verify_self(&self) -> bool {
-        self.id == next_hash(&self.prev_id, self.num_hashes, &self.transactions)
-    }
-
     /// Verifies self.id is the result of hashing a `start_hash` `self.num_hashes` times.
     /// If the transaction is not a Tick, then hash that as well.
     pub fn verify(&self, start_hash: &Hash) -> bool {
@@ -260,7 +248,6 @@ pub fn reconstruct_entries_from_blobs(blobs: Vec<SharedBlob>) -> Result<(Vec<Ent
 pub fn next_entry(prev_id: &Hash, num_hashes: u64, transactions: Vec<Transaction>) -> Entry {
     assert!(num_hashes > 0 || transactions.is_empty());
     Entry {
-        prev_id: *prev_id,
         tick_height: 0,
         num_hashes,
         id: next_hash(prev_id, num_hashes, &transactions),
@@ -283,10 +270,9 @@ mod tests {
     fn test_entry_verify() {
         let zero = Hash::default();
         let one = hash(&zero.as_ref());
-        assert!(Entry::new_tick(&zero, 0, 0, &zero).verify(&zero)); // base case, never used
+        assert!(Entry::new_tick(0, 0, &zero).verify(&zero)); // base case, never used
-        assert!(!Entry::new_tick(&zero, 1, 0, &zero).verify(&one)); // base case, bad
+        assert!(!Entry::new_tick(1, 0, &zero).verify(&one)); // base case, bad
         assert!(next_entry(&zero, 1, vec![]).verify(&zero)); // inductive step
-        assert!(next_entry(&zero, 1, vec![]).verify_self()); // also inductive step
         assert!(!next_entry(&zero, 1, vec![]).verify(&one)); // inductive step, bad
     }
 

src/ledger.rs

@@ -457,7 +457,6 @@ pub trait Block {
 impl Block for [Entry] {
     fn verify(&self, start_hash: &Hash) -> bool {
         let genesis = [Entry {
-            prev_id: *start_hash,
             tick_height: 0,
             num_hashes: 0,
             id: *start_hash,
@@ -737,8 +736,8 @@ mod tests {
         let zero = Hash::default();
         let one = hash(&zero.as_ref());
         assert!(vec![][..].verify(&zero)); // base case
-        assert!(vec![Entry::new_tick(&zero, 0, 0, &zero)][..].verify(&zero)); // singleton case 1
+        assert!(vec![Entry::new_tick(0, 0, &zero)][..].verify(&zero)); // singleton case 1
-        assert!(!vec![Entry::new_tick(&zero, 0, 0, &zero)][..].verify(&one)); // singleton case 2, bad
+        assert!(!vec![Entry::new_tick(0, 0, &zero)][..].verify(&one)); // singleton case 2, bad
         assert!(vec![next_entry(&zero, 0, vec![]); 2][..].verify(&zero)); // inductive step
 
         let mut bad_ticks = vec![next_entry(&zero, 0, vec![]); 2];
@@ -808,7 +807,6 @@ mod tests {
         let tx_small_size = serialized_size(&tx_small).unwrap() as usize;
         let tx_large_size = serialized_size(&tx_large).unwrap() as usize;
         let entry_size = serialized_size(&Entry {
-            prev_id: Hash::default(),
             tick_height: 0,
             num_hashes: 0,
             id: Hash::default(),

src/poh.rs

@@ -3,7 +3,6 @@
 use solana_sdk::hash::{hash, hashv, Hash};
 
 pub struct Poh {
-    prev_id: Hash,
     id: Hash,
     num_hashes: u64,
     pub tick_height: u64,
@@ -11,7 +10,6 @@ pub struct Poh {
 
 #[derive(Debug)]
 pub struct PohEntry {
-    pub prev_id: Hash,
     pub tick_height: u64,
     pub num_hashes: u64,
     pub id: Hash,
@@ -19,11 +17,10 @@ pub struct PohEntry {
 }
 
 impl Poh {
-    pub fn new(prev_id: Hash, tick_height: u64) -> Self {
+    pub fn new(id: Hash, tick_height: u64) -> Self {
         Poh {
-            prev_id,
             num_hashes: 0,
-            id: prev_id,
+            id,
             tick_height,
         }
     }
@@ -36,14 +33,10 @@ impl Poh {
     pub fn record(&mut self, mixin: Hash) -> PohEntry {
         self.id = hashv(&[&self.id.as_ref(), &mixin.as_ref()]);
 
-        let prev_id = self.prev_id;
-        self.prev_id = self.id;
-
         let num_hashes = self.num_hashes + 1;
         self.num_hashes = 0;
 
         PohEntry {
-            prev_id,
             tick_height: self.tick_height,
             num_hashes,
             id: self.id,
@@ -59,14 +52,10 @@ impl Poh {
         let num_hashes = self.num_hashes;
         self.num_hashes = 0;
 
-        let prev_id = self.prev_id;
-        self.prev_id = self.id;
-
         let tick_height = self.tick_height;
         self.tick_height += 1;
 
         PohEntry {
-            prev_id,
             tick_height,
             num_hashes,
             id: self.id,
@@ -77,20 +66,19 @@ impl Poh {
 
 #[cfg(test)]
 pub fn verify(initial: Hash, entries: &[PohEntry]) -> bool {
-    let mut prev_id = initial;
+    let mut id = initial;
 
     for entry in entries {
         assert!(entry.num_hashes != 0);
-        assert!(prev_id == entry.prev_id);
 
         for _ in 1..entry.num_hashes {
-            prev_id = hash(&prev_id.as_ref());
+            id = hash(&id.as_ref());
         }
-        prev_id = match entry.mixin {
+        id = match entry.mixin {
-            Some(mixin) => hashv(&[&prev_id.as_ref(), &mixin.as_ref()]),
+            Some(mixin) => hashv(&[&id.as_ref(), &mixin.as_ref()]),
-            None => hash(&prev_id.as_ref()),
+            None => hash(&id.as_ref()),
         };
-        if prev_id != entry.id {
+        if id != entry.id {
             return false;
         }
     }
@@ -109,7 +97,6 @@ mod tests {
         poh::verify(
             Hash::default(),
             &[PohEntry {
-                prev_id: Hash::default(),
                 tick_height: 0,
                 num_hashes: 0,
                 id: Hash::default(),

src/poh_recorder.rs

@@ -89,7 +89,6 @@ impl PohRecorder {
         let entry = poh.record(mixin);
         assert!(!txs.is_empty(), "Entries without transactions are used to track real-time passing in the ledger and can only be generated with PohRecorder::tick function");
         let entry = Entry {
-            prev_id: entry.prev_id,
             tick_height: entry.tick_height,
             num_hashes: entry.num_hashes,
             id: entry.id,
@@ -102,7 +101,6 @@ impl PohRecorder {
     fn register_and_send_tick(&self, poh: &mut Poh) -> Result<()> {
         let tick = poh.tick();
         let tick = Entry {
-            prev_id: tick.prev_id,
             tick_height: tick.tick_height,
             num_hashes: tick.num_hashes,
             id: tick.id,