fix edgecases around small data slices or few sequences

KillingSpark · Nov 21, 2024 · 61c3480 · 61c3480
1 parent 4dc00ee
commit 61c3480
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Showing 2 changed files with 32 additions and 28 deletions.
diff --git a/src/encoding/blocks/compressed.rs b/src/encoding/blocks/compressed.rs
@@ -71,34 +71,36 @@ pub fn compress_block<'a>(matcher: &mut MatchGenerator<'a>, data: &'a [u8], outp
         writer.write_bits(of_add_bits, of_num_bits);
 
         // encode backwards so the decoder reads the first sequence first
-        for sequence in (0..=sequences.len() - 2).rev() {
-            let sequence = sequences[sequence];
-            let (ll_code, ll_add_bits, ll_num_bits) = encode_literal_length(sequence.ll);
-            let (of_code, of_add_bits, of_num_bits) = encode_offset(sequence.of);
-            let (ml_code, ml_add_bits, ml_num_bits) = encode_match_len(sequence.ml);
-
-            {
-                let next = of_table.next_state(of_code, of_state.index);
-                let diff = of_state.index - next.baseline;
-                writer.write_bits(diff as u64, next.num_bits as usize);
-                of_state = next;
+        if sequences.len() > 1 {
+            for sequence in (0..=sequences.len() - 2).rev() {
+                let sequence = sequences[sequence];
+                let (ll_code, ll_add_bits, ll_num_bits) = encode_literal_length(sequence.ll);
+                let (of_code, of_add_bits, of_num_bits) = encode_offset(sequence.of);
+                let (ml_code, ml_add_bits, ml_num_bits) = encode_match_len(sequence.ml);
+
+                {
+                    let next = of_table.next_state(of_code, of_state.index);
+                    let diff = of_state.index - next.baseline;
+                    writer.write_bits(diff as u64, next.num_bits as usize);
+                    of_state = next;
+                }
+                {
+                    let next = ml_table.next_state(ml_code, ml_state.index);
+                    let diff = ml_state.index - next.baseline;
+                    writer.write_bits(diff as u64, next.num_bits as usize);
+                    ml_state = next;
+                }
+                {
+                    let next = ll_table.next_state(ll_code, ll_state.index);
+                    let diff = ll_state.index - next.baseline;
+                    writer.write_bits(diff as u64, next.num_bits as usize);
+                    ll_state = next;
+                }
+
+                writer.write_bits(ll_add_bits, ll_num_bits);
+                writer.write_bits(ml_add_bits, ml_num_bits);
+                writer.write_bits(of_add_bits, of_num_bits);
             }
-            {
-                let next = ml_table.next_state(ml_code, ml_state.index);
-                let diff = ml_state.index - next.baseline;
-                writer.write_bits(diff as u64, next.num_bits as usize);
-                ml_state = next;
-            }
-            {
-                let next = ll_table.next_state(ll_code, ll_state.index);
-                let diff = ll_state.index - next.baseline;
-                writer.write_bits(diff as u64, next.num_bits as usize);
-                ll_state = next;
-            }
-
-            writer.write_bits(ll_add_bits, ll_num_bits);
-            writer.write_bits(ml_add_bits, ml_num_bits);
-            writer.write_bits(of_add_bits, of_num_bits);
         }
         writer.write_bits(ml_state.index as u64, ml_table.table_size.ilog2() as usize);
         writer.write_bits(of_state.index as u64, of_table.table_size.ilog2() as usize);

diff --git a/src/encoding/match_generator.rs b/src/encoding/match_generator.rs
@@ -100,7 +100,6 @@ impl<'data> MatchGenerator<'data> {
                         let literals = &last_entry.data[self.last_idx_in_sequence..self.suffix_idx];
                         let offset = match_entry.base_offset + self.suffix_idx - match_index;
 
-
                         #[cfg(debug_assertions)]
                         {
                             let unprocessed = last_entry.data.len() - self.suffix_idx;
@@ -139,6 +138,9 @@ impl<'data> MatchGenerator<'data> {
 
     fn add_suffixes_till(&mut self, idx: usize) {
         let last_entry = self.window.last_mut().unwrap();
+        if last_entry.data.len() < MIN_MATCH_LEN {
+            return;
+        }
         let last_idx = usize::min(idx, last_entry.data.len() - MIN_MATCH_LEN);
         for idx in self.suffix_idx..=last_idx {
             let mut key = [0u8; MIN_MATCH_LEN];