[TieredStorage] Add IndexPosition type

accounts-db/src/tiered_storage/index.rs

@@ -38,6 +38,11 @@ pub enum AccountIndexFormat {
     AddressAndOffset = 0,
 }
 
+/// The position of an account/address entry in the accounts index block.
+/// This can be used to obtain the AccountOffset and address by looking through
+/// the accounts index block.
+pub struct IndexPosition(usize);
+
 impl AccountIndexFormat {
     /// Persists the specified index_entries to the specified file and returns
     /// the total number of bytes written.
@@ -65,11 +70,11 @@ impl AccountIndexFormat {
         &self,
         map: &'a Mmap,
         footer: &TieredStorageFooter,
-        index: usize,
+        index: IndexPosition,
     ) -> TieredStorageResult<&'a Pubkey> {
         let offset = match self {
             Self::AddressAndOffset => {
-                footer.account_index_offset as usize + std::mem::size_of::<Pubkey>() * index
+                footer.account_index_offset as usize + std::mem::size_of::<Pubkey>() * index.0
             }
         };
         let (address, _) = get_type::<Pubkey>(map, offset)?;
@@ -82,13 +87,13 @@ impl AccountIndexFormat {
         &self,
         map: &Mmap,
         footer: &TieredStorageFooter,
-        index: usize,
+        index: IndexPosition,
     ) -> TieredStorageResult<u64> {
         match self {
             Self::AddressAndOffset => {
                 let offset = footer.account_index_offset as usize
                     + std::mem::size_of::<Pubkey>() * footer.account_entry_count as usize
-                    + index * std::mem::size_of::<u64>();
+                    + index.0 * std::mem::size_of::<u64>();
                 let (account_block_offset, _) = get_type(map, offset)?;
                 Ok(*account_block_offset)
             }
@@ -148,9 +153,13 @@ mod tests {
         for (i, index_entry) in index_entries.iter().enumerate() {
             assert_eq!(
                 index_entry.block_offset,
-                indexer.get_account_block_offset(&map, &footer, i).unwrap()
+                indexer
+                    .get_account_block_offset(&map, &footer, IndexPosition(i))
+                    .unwrap()
             );
-            let address = indexer.get_account_address(&map, &footer, i).unwrap();
+            let address = indexer
+                .get_account_address(&map, &footer, IndexPosition(i))
+                .unwrap();
             assert_eq!(index_entry.address, address);
         }
     }