Clarify postings copy variable names

Author: PSeitz

src/postings/block_segment_postings.rs

@@ -242,20 +242,20 @@ impl BlockSegmentPostings {
 
     pub(crate) fn copy_docs_and_term_freqs(
         &self,
-        start: usize,
+        block_offset: usize,
         horizon: DocId,
         docs: &mut [DocId],
         term_freqs: &mut [u32],
     ) -> usize {
         debug_assert_eq!(docs.len(), term_freqs.len());
         let block_docs = self.docs();
-        let available = block_docs.len().saturating_sub(start);
-        let max_len = available.min(docs.len());
+        let remaining_docs_in_block = block_docs.len().saturating_sub(block_offset);
+        let max_len = remaining_docs_in_block.min(docs.len());
         if max_len == 0 {
             return 0;
         }
 
-        let source_docs = &block_docs[start..start + max_len];
+        let source_docs = &block_docs[block_offset..block_offset + max_len];
         let len = if source_docs[max_len - 1] < horizon {
             max_len
         } else {
@@ -268,8 +268,8 @@ impl BlockSegmentPostings {
         docs[..len].copy_from_slice(&source_docs[..len]);
 
         let block_freqs = self.freq_output_array();
-        if block_freqs.len() >= start + len {
-            term_freqs[..len].copy_from_slice(&block_freqs[start..start + len]);
+        if block_freqs.len() >= block_offset + len {
+            term_freqs[..len].copy_from_slice(&block_freqs[block_offset..block_offset + len]);
         } else {
             term_freqs[..len].fill(1);
         }

src/postings/segment_postings.rs

@@ -158,26 +158,26 @@ impl SegmentPostings {
         docs: &mut [DocId; COLLECT_BLOCK_BUFFER_LEN],
         term_freqs: &mut [u32; COLLECT_BLOCK_BUFFER_LEN],
     ) -> usize {
-        let mut filled = 0;
-        while filled < COLLECT_BLOCK_BUFFER_LEN && self.doc() < horizon {
+        let mut num_elems = 0;
+        while num_elems < COLLECT_BLOCK_BUFFER_LEN && self.doc() < horizon {
             let copied = self.block_cursor.copy_docs_and_term_freqs(
                 self.cur,
                 horizon,
-                &mut docs[filled..],
-                &mut term_freqs[filled..],
+                &mut docs[num_elems..],
+                &mut term_freqs[num_elems..],
             );
             if copied == 0 {
                 break;
             }
-            filled += copied;
+            num_elems += copied;
             self.cur += copied;
 
             if self.cur == COMPRESSION_BLOCK_SIZE {
                 self.cur = 0;
                 self.block_cursor.advance();
             }
         }
-        filled
+        num_elems
     }
 }