Support patterns shorter than 3 bytes.

This isn't very efficient, but it appears to still be slightly better
than mlocate.

diff --git a/plocate.cpp b/plocate.cpp
index 138eb36705473458d8d04cd64313292aa36db55f..3d30adbbc5dd5a7bd04c0925bc60591501d33746 100644 (file)
--- a/plocate.cpp
+++ b/plocate.cpp
@@ -74,6 +74,7 @@ public:
        const unsigned char *
        get_compressed_posting_list(const Trigram *trigram) const;
        string_view get_compressed_filename_block(uint32_t docid) const;
+       size_t get_num_filename_blocks() const;
 
 private:
        const int fd;
@@ -137,6 +138,15 @@ string_view Corpus::get_compressed_filename_block(uint32_t docid) const
        return { compressed, compressed_size };
 }
 
+size_t Corpus::get_num_filename_blocks() const
+{
+       // The beginning of the filename blocks is the end of the filename index blocks.
+       const uint64_t *filename_offsets_end = (const uint64_t *)(data + filename_offsets[0]);
+
+       // Subtract the sentinel block.
+       return filename_offsets_end - filename_offsets - 1;
+}
+
 size_t scan_docid(const string &needle, uint32_t docid, const Corpus &corpus,
                   unordered_map<string, bool> *access_rx_cache)
 {
@@ -187,6 +197,19 @@ void do_search_file(const string &needle, const char *filename)
 
        Corpus corpus(fd);
 
+       if (needle.size() < 3) {
+               // Too short for trigram matching. Apply brute force.
+               // (We could have searched through all trigrams that matched
+               // the pattern and done a union of them, but that's a lot of
+               // work for fairly unclear gain.)
+               unordered_map<string, bool> access_rx_cache;
+               uint32_t num_blocks = corpus.get_num_filename_blocks();
+               for (uint32_t docid = 0; docid < num_blocks; ++docid) {
+                       scan_docid(needle, docid, corpus, &access_rx_cache);
+               }
+               return;
+       }
+
        vector<const Trigram *> trigrams;
        for (size_t i = 0; i < needle.size() - 2; ++i) {
                uint32_t trgm = read_trigram(needle, i);