Move transaction capacity formula to Format

libraries/persistent_store/src/format.rs

@@ -18,7 +18,7 @@ mod bitfield;
 #[cfg(test)]
 use self::bitfield::Length;
 use self::bitfield::{count_zeros, num_bits, Bit, Checksum, ConstField, Field};
-use crate::{usize_to_nat, Nat, Storage, StorageIndex, StoreError, StoreResult};
+use crate::{usize_to_nat, Nat, Storage, StorageIndex, StoreError, StoreResult, StoreUpdate};
 use alloc::vec::Vec;
 use core::cmp::min;
 use core::convert::TryFrom;
@@ -491,6 +491,35 @@ impl Format {
         HEADER_DELETED.set(word);
     }
 
+    /// Returns the capacity required by a transaction.
+    pub fn transaction_capacity(&self, updates: &[StoreUpdate]) -> Nat {
+        match updates.len() {
+            // An empty transaction doesn't consume anything.
+            0 => 0,
+            // Transactions with a single update are optimized by avoiding a marker entry.
+            1 => match &updates[0] {
+                StoreUpdate::Insert { value, .. } => self.entry_size(value),
+                // Transactions with a single update which is a removal don't consume anything.
+                StoreUpdate::Remove { .. } => 0,
+            },
+            // A transaction consumes one word for the marker entry in addition to its updates.
+            _ => 1 + updates.iter().map(|x| self.update_capacity(x)).sum::<Nat>(),
+        }
+    }
+
+    /// Returns the capacity of an update.
+    fn update_capacity(&self, update: &StoreUpdate) -> Nat {
+        match update {
+            StoreUpdate::Insert { value, .. } => self.entry_size(value),
+            StoreUpdate::Remove { .. } => 1,
+        }
+    }
+
+    /// Returns the size of a user entry given its value.
+    pub fn entry_size(&self, value: &[u8]) -> Nat {
+        1 + self.bytes_to_words(usize_to_nat(value.len()))
+    }
+
     /// Returns the minimum number of words to represent a given number of bytes.
     ///
     /// # Preconditions

libraries/persistent_store/src/model.rs

@@ -79,7 +79,12 @@ impl StoreModel {
     /// Returns the capacity according to the model.
     pub fn capacity(&self) -> StoreRatio {
         let total = self.format.total_capacity();
-        let used = usize_to_nat(self.content.values().map(|x| self.entry_size(x)).sum());
+        let used = usize_to_nat(
+            self.content
+                .values()
+                .map(|x| self.format.entry_size(x) as usize)
+                .sum(),
+        );
         StoreRatio { used, total }
     }
 
@@ -99,18 +104,7 @@ impl StoreModel {
             return Err(StoreError::InvalidArgument);
         }
         // Fail if there is not enough capacity.
-        let capacity = match updates.len() {
-            // An empty transaction doesn't consume anything.
-            0 => 0,
-            // Transactions with a single update are optimized by avoiding a marker entry.
-            1 => match &updates[0] {
-                StoreUpdate::Insert { value, .. } => self.entry_size(value),
-                // Transactions with a single update which is a removal don't consume anything.
-                StoreUpdate::Remove { .. } => 0,
-            },
-            // A transaction consumes one word for the marker entry in addition to its updates.
-            _ => 1 + updates.iter().map(|x| self.update_size(x)).sum::<usize>(),
-        };
+        let capacity = self.format.transaction_capacity(&updates) as usize;
         if self.capacity().remaining() < capacity {
             return Err(StoreError::NoCapacity);
         }
@@ -145,19 +139,6 @@ impl StoreModel {
         Ok(())
     }
 
-    /// Returns the word capacity of an update.
-    fn update_size(&self, update: &StoreUpdate) -> usize {
-        match update {
-            StoreUpdate::Insert { value, .. } => self.entry_size(value),
-            StoreUpdate::Remove { .. } => 1,
-        }
-    }
-
-    /// Returns the word capacity of an entry.
-    fn entry_size(&self, value: &[u8]) -> usize {
-        1 + self.format.bytes_to_words(usize_to_nat(value.len())) as usize
-    }
-
     /// Returns whether an update is valid.
     fn update_valid(&self, update: &StoreUpdate) -> bool {
         update.key() <= self.format.max_key() as usize

libraries/persistent_store/src/store.rs

@@ -262,20 +262,17 @@ impl<S: Storage> Store<S> {
         if count > self.format.max_updates() {
             return Err(StoreError::InvalidArgument);
         }
-        // Compute how much capacity (including transient) we need.
+        // Check that the updates are valid.
         let mut sorted_keys = Vec::with_capacity(count as usize);
-        let mut word_capacity = 1 + count;
         for update in updates {
             let key = usize_to_nat(update.key());
             if key > self.format.max_key() {
                 return Err(StoreError::InvalidArgument);
             }
             if let Some(value) = update.value() {
-                let value_len = usize_to_nat(value.len());
-                if value_len > self.format.max_value_len() {
+                if usize_to_nat(value.len()) > self.format.max_value_len() {
                     return Err(StoreError::InvalidArgument);
                 }
-                word_capacity += self.format.bytes_to_words(value_len);
             }
             match sorted_keys.binary_search(&key) {
                 Ok(_) => return Err(StoreError::InvalidArgument),
@@ -283,7 +280,7 @@ impl<S: Storage> Store<S> {
             }
         }
         // Reserve the capacity.
-        self.reserve(word_capacity)?;
+        self.reserve(self.format.transaction_capacity(updates))?;
         // Write the marker entry.
         let marker = self.tail()?;
         let entry = self.format.build_internal(InternalEntry::Marker { count });