Remove duplicate def of MAX_SLOT_HASHES (#7574)

sdk/benches/slot_hashes.rs

@@ -0,0 +1,23 @@
+#![feature(test)]
+
+extern crate test;
+use solana_sdk::{
+    hash::Hash,
+    slot_hashes::{Slot, SlotHashes, MAX_SLOT_HASHES},
+    sysvar::Sysvar,
+};
+use test::Bencher;
+
+#[bench]
+fn bench_to_from_account(b: &mut Bencher) {
+    let mut slot_hashes = SlotHashes::new(&[]);
+    for i in 0..MAX_SLOT_HASHES {
+        slot_hashes.add(i as Slot, Hash::default());
+    }
+    let mut reps = 0;
+    b.iter(|| {
+        reps += 1;
+        let account = slot_hashes.create_account(0);
+        slot_hashes = SlotHashes::from_account(&account).unwrap();
+    });
+}

sdk/src/slot_hashes.rs

@@ -3,9 +3,9 @@
 //! this account carries the Bank's most recent blockhashes for some N parents
 //!
 use crate::hash::Hash;
-use std::ops::Deref;
+use std::{iter::FromIterator, ops::Deref};
 
-pub const MAX_SLOT_HASHES: usize = 512; // 512 slots to get your vote in
+pub const MAX_SLOT_HASHES: usize = 512; // about 2.5 minutes to get your vote in
 
 pub use crate::clock::Slot;
 
@@ -17,7 +17,7 @@ pub struct SlotHashes(Vec<SlotHash>);
 
 impl SlotHashes {
     pub fn add(&mut self, slot: Slot, hash: Hash) {
-        match self.binary_search_by(|probe| slot.cmp(&probe.0)) {
+        match self.binary_search_by(|(probe, _)| slot.cmp(&probe)) {
             Ok(index) => (self.0)[index] = (slot, hash),
             Err(index) => (self.0).insert(index, (slot, hash)),
         }
@@ -25,17 +25,23 @@ impl SlotHashes {
     }
     #[allow(clippy::trivially_copy_pass_by_ref)]
     pub fn get(&self, slot: &Slot) -> Option<&Hash> {
-        self.binary_search_by(|probe| slot.cmp(&probe.0))
+        self.binary_search_by(|(probe, _)| slot.cmp(&probe))
             .ok()
             .map(|index| &self[index].1)
     }
     pub fn new(slot_hashes: &[SlotHash]) -> Self {
         let mut slot_hashes = slot_hashes.to_vec();
-        slot_hashes.sort_by(|a, b| b.0.cmp(&a.0)); // reverse order
+        slot_hashes.sort_by(|(a, _), (b, _)| b.cmp(a));
         Self(slot_hashes)
     }
 }
 
+impl FromIterator<(Slot, Hash)> for SlotHashes {
+    fn from_iter<I: IntoIterator<Item = (Slot, Hash)>>(iter: I) -> Self {
+        Self(iter.into_iter().collect())
+    }
+}
+
 impl Deref for SlotHashes {
     type Target = Vec<SlotHash>;
     fn deref(&self) -> &Self::Target {

sdk/src/sysvar/slot_hashes.rs

@@ -2,17 +2,17 @@
 //!
 //! this account carries the Bank's most recent blockhashes for some N parents
 //!
-pub use crate::slot_hashes::{SlotHash, SlotHashes};
-use crate::{account::Account, sysvar::Sysvar};
+pub use crate::slot_hashes::{Slot, SlotHash, SlotHashes, MAX_SLOT_HASHES};
+use crate::{account::Account, hash::Hash, sysvar::Sysvar};
 
 crate::declare_sysvar_id!("SysvarS1otHashes111111111111111111111111111", SlotHashes);
 
-pub const MAX_SLOT_HASHES: usize = 512; // 512 slots to get your vote in
-
 impl Sysvar for SlotHashes {
     fn biggest() -> Self {
         // override
-        SlotHashes::new(&[SlotHash::default(); MAX_SLOT_HASHES])
+        (0..MAX_SLOT_HASHES)
+            .map(|slot| (slot as Slot, Hash::default()))
+            .collect::<Self>()
     }
 }