Replace std::string with std::vector<unsigned char> when encoding posting lists.

This is a ~0.5–1% win since we never use the short-string optimization,
and the vector fits better in cache.

diff --git a/database-builder.cpp b/database-builder.cpp
index 439e25a59e88980ef6a2f8f7bb9d38c43f7134ec..11a1a5a72b0cefd6cda59ecce997c4b1fb8c5b1c 100644 (file)
--- a/database-builder.cpp
+++ b/database-builder.cpp
@@ -48,7 +48,7 @@ public:
        inline void add_first_docid(uint32_t docid);
        void finish();
 
-       string encoded;
+       vector<unsigned char> encoded;
        size_t num_docids = 0;
 
 private:
@@ -96,7 +96,7 @@ void PostingListBuilder::finish()
        // No interleaving for partial blocks.
        unsigned char buf[P4NENC_BOUND(128)];
        unsigned char *end = encode_pfor_single_block<128>(pending_deltas.data(), pending_deltas.size(), /*interleaved=*/false, buf);
-       encoded.append(reinterpret_cast<char *>(buf), reinterpret_cast<char *>(end));
+       encoded.insert(encoded.end(), buf, end);
 }
 
 void PostingListBuilder::append_block()
@@ -104,14 +104,14 @@ void PostingListBuilder::append_block()
        unsigned char buf[P4NENC_BOUND(128)];
        assert(pending_deltas.size() == 128);
        unsigned char *end = encode_pfor_single_block<128>(pending_deltas.data(), 128, /*interleaved=*/true, buf);
-       encoded.append(reinterpret_cast<char *>(buf), reinterpret_cast<char *>(end));
+       encoded.insert(encoded.end(), buf, end);
 }
 
 void PostingListBuilder::write_header(uint32_t docid)
 {
        unsigned char buf[P4NENC_BOUND(1)];
        unsigned char *end = write_baseval(docid, buf);
-       encoded.append(reinterpret_cast<char *>(buf), end - buf);
+       encoded.insert(encoded.end(), buf, end);
 }
 
 void DictionaryBuilder::add_file(string filename, dir_time)
@@ -617,7 +617,7 @@ void DatabaseBuilder::finish_corpus()
                        continue;
                }
 
-               const string &encoded = corpus->get_pl_builder(hashtable[i].trgm).encoded;
+               const vector<unsigned char> &encoded = corpus->get_pl_builder(hashtable[i].trgm).encoded;
                offset += encoded.size();
        }
 
@@ -631,7 +631,7 @@ void DatabaseBuilder::finish_corpus()
                if (hashtable[i].num_docids == 0) {
                        continue;
                }
-               const string &encoded = corpus->get_pl_builder(hashtable[i].trgm).encoded;
+               const vector<unsigned char> &encoded = corpus->get_pl_builder(hashtable[i].trgm).encoded;
                fwrite(encoded.data(), encoded.size(), 1, outfp);
        }