fix: Arrays with negative values cannot be encoded like bitpacked arrays (#2917)

Author: robert3005

encodings/fastlanes/src/bitpacking/compress.rs

@@ -32,7 +32,7 @@ pub fn bitpack_encode(array: &PrimitiveArray, bit_width: u8) -> VortexResult<Bit
     // Check array contains no negative values.
     if array.ptype().is_signed_int() {
         let has_negative_values = match_each_integer_ptype!(array.ptype(), |$P| {
-            array.statistics().compute_min::<Option<$P>>().unwrap_or_default().unwrap_or_default() < 0
+            array.statistics().compute_min::<$P>().unwrap_or_default() < 0
         });
         if has_negative_values {
             vortex_bail!("cannot bitpack_encode array containing negative integers")

encodings/fastlanes/src/bitpacking/serde.rs

@@ -115,7 +115,10 @@ impl EncodingVTable for BitPackedEncoding {
             None => find_best_bit_width(&parray)?,
         };
 
-        let array = if bit_width as usize == parray.ptype().bit_width() {
+        let array = if bit_width as usize == parray.ptype().bit_width()
+            || parray.ptype().is_signed_int()
+                && parray.statistics().compute_min::<i64>().unwrap_or_default() < 0
+        {
             parray.into_array()
         } else {
             bitpack_encode(&parray, bit_width)?.into_array()

vortex-file/src/strategy.rs

@@ -139,12 +139,12 @@ impl LayoutWriter for BtrBlocksCompressedWriter {
         else if let Some(prev_compression) = self.previous_chunk.as_ref() {
             let prev_chunk = prev_compression.chunk.clone();
             let canonical_chunk = chunk.to_canonical()?;
+            let canonical_nbytes = canonical_chunk.as_ref().nbytes();
 
             if let Some(encoded_chunk) =
-                encode_children_like(canonical_chunk.clone().into_array(), prev_chunk)?
+                encode_children_like(canonical_chunk.into_array(), prev_chunk)?
             {
-                let ratio =
-                    canonical_chunk.as_ref().nbytes() as f64 / encoded_chunk.nbytes() as f64;
+                let ratio = canonical_nbytes as f64 / encoded_chunk.nbytes() as f64;
 
                 // Make sure the ratio is within the expected drift, if it isn't we  fall back to the compressor.
                 if ratio > prev_compression.ratio / COMPRESSION_DRIFT_THRESHOLD {