refactor

bitpacker/src/blocked_bitpacker.rs

@@ -12,7 +12,7 @@ pub struct BlockedBitpacker {
     // bitpacked blocks
     compressed_blocks: Vec<u8>,
     // uncompressed data, collected until BLOCK_SIZE
-    cache: Vec<u64>,
+    buffer: Vec<u64>,
     offset_and_bits: Vec<BlockedBitpackerEntryMetaData>,
 }
 
@@ -60,7 +60,7 @@ impl BlockedBitpacker {
         compressed_blocks.resize(8, 0);
         Self {
             compressed_blocks,
-            cache: vec![],
+            buffer: vec![],
             offset_and_bits: vec![],
         }
     }
@@ -71,56 +71,58 @@ impl BlockedBitpacker {
             + self.compressed_blocks.capacity()
             + self.offset_and_bits.capacity()
                 * std::mem::size_of_val(&self.offset_and_bits.get(0).cloned().unwrap_or_default())
-            + self.cache.capacity()
-                * std::mem::size_of_val(&self.cache.get(0).cloned().unwrap_or_default())
+            + self.buffer.capacity()
+                * std::mem::size_of_val(&self.buffer.get(0).cloned().unwrap_or_default())
     }
 
     pub fn add(&mut self, val: u64) {
-        self.cache.push(val);
-        if self.cache.len() == BLOCK_SIZE as usize {
+        self.buffer.push(val);
+        if self.buffer.len() == BLOCK_SIZE as usize {
             self.flush();
         }
     }
 
     pub fn flush(&mut self) {
-        if self.cache.is_empty() {
+        if let Some(min_value) = self.buffer.iter().min() {
+            let mut bit_packer = BitPacker::new();
+            let num_bits_block = self
+                .buffer
+                .iter()
+                .map(|val| compute_num_bits(*val - min_value))
+                .max()
+                .unwrap();
+            // todo performance: the padding handling could be done better, e.g. use a slice and
+            // return num_bytes written from bitpacker
+            self.compressed_blocks
+                .resize(self.compressed_blocks.len() - 8, 0); // remove padding for bitpacker
+            let offset = self.compressed_blocks.len() as u64;
+            // todo performance: for some bit_width we
+            // can encode multiple vals into the
+            // mini_buffer before checking to flush
+            // (to be done in BitPacker)
+            for val in self.buffer.iter() {
+                bit_packer
+                    .write(
+                        *val - min_value,
+                        num_bits_block,
+                        &mut self.compressed_blocks,
+                    )
+                    .expect("cannot write bitpacking to output"); // write to in memory can't fail
+            }
+            bit_packer.flush(&mut self.compressed_blocks).unwrap();
+            self.offset_and_bits
+                .push(BlockedBitpackerEntryMetaData::new(
+                    offset,
+                    num_bits_block,
+                    *min_value,
+                ));
+
+            self.buffer.clear();
+            self.compressed_blocks
+                .resize(self.compressed_blocks.len() + 8, 0); // add padding for bitpacker
+        } else {
             return;
         }
-        let mut bit_packer = BitPacker::new();
-        let base_value = self.cache.iter().min().unwrap();
-        let num_bits_block = self
-            .cache
-            .iter()
-            .map(|val| compute_num_bits(*val - base_value))
-            .max()
-            .unwrap();
-        self.compressed_blocks
-            .resize(self.compressed_blocks.len() - 8, 0); // remove padding for bitpacker
-        let offset = self.compressed_blocks.len() as u64;
-        // todo performance: for some bit_width we
-        // can encode multiple vals into the
-        // mini_buffer before checking to flush
-        // (to be done in BitPacker)
-        for val in self.cache.iter() {
-            bit_packer
-                .write(
-                    *val - base_value,
-                    num_bits_block,
-                    &mut self.compressed_blocks,
-                )
-                .expect("cannot write bitpacking to output"); // write to im can't fail
-        }
-        bit_packer.flush(&mut self.compressed_blocks).unwrap();
-        self.offset_and_bits
-            .push(BlockedBitpackerEntryMetaData::new(
-                offset,
-                num_bits_block,
-                *base_value,
-            ));
-
-        self.cache.clear();
-        self.compressed_blocks
-            .resize(self.compressed_blocks.len() + 8, 0); // add padding for bitpacker
     }
     pub fn get(&self, idx: usize) -> u64 {
         let metadata_pos = idx / BLOCK_SIZE as usize;
@@ -132,7 +134,7 @@ impl BlockedBitpacker {
             );
             unpacked + metadata.base_value()
         } else {
-            self.cache[pos_in_block]
+            self.buffer[pos_in_block]
         }
     }
 
@@ -141,7 +143,7 @@ impl BlockedBitpacker {
         let bitpacked_elems = self.offset_and_bits.len() * BLOCK_SIZE;
         let iter = (0..bitpacked_elems)
             .map(move |idx| self.get(idx))
-            .chain(self.cache.iter().cloned());
+            .chain(self.buffer.iter().cloned());
         iter
     }
 }