Fix a number of performance issues (reported by Coverity Scan)

Coverity Scan reports "Unnecessary object copies can affect performance"
and suggests using the auto keyword with an &.

Signed-off-by: Stefan Weil <[email protected]>

Author: stweil

src/api/hocrrenderer.cpp

@@ -412,7 +412,7 @@ char *TessBaseAPI::GetHOCRText(ETEXT_DESC *monitor, int page_number) {
                    << " id='"
                    << "timestep" << page_id << "_" << wcnt << "_" << tcnt
                    << "'>";
-          for (auto conf : timestep) {
+          for (auto &&conf : timestep) {
             hocr_str << "\n         <span class='ocrx_cinfo'"
                      << " id='"
                      << "choice_" << page_id << "_" << wcnt << "_" << ccnt

src/ccmain/control.cpp

@@ -1191,7 +1191,7 @@ bool Tesseract::SelectGoodDiacriticOutlines(int pass, float certainty_threshold,
     *ok_outlines = best_outlines;
     if (debug_noise_removal) {
       tprintf("%s noise combination ", blob ? "Adding" : "New");
-      for (auto best_outline : best_outlines) {
+      for (auto &&best_outline : best_outlines) {
         tprintf("%c", best_outline ? 'T' : 'F');
       }
       tprintf(" yields certainty %g, beating target of %g\n", best_cert, target_cert);

src/ccstruct/fontinfo.cpp

@@ -67,7 +67,7 @@ bool FontInfoTable::DeSerialize(TFile *fp) {
 bool FontInfoTable::SetContainsFontProperties(int font_id,
                                               const std::vector<ScoredFont> &font_set) const {
   uint32_t properties = at(font_id).properties;
-  for (auto f : font_set) {
+  for (auto &&f : font_set) {
     if (at(f.fontinfo_id).properties == properties) {
       return true;
     }

src/ccutil/serialis.h

@@ -157,7 +157,7 @@ class TESS_API TFile {
       return false;
     } else if constexpr (std::is_same<T, std::string>::value) {
       // Serialize strings.
-      for (auto string : data) {
+      for (auto &&string : data) {
         if (!Serialize(string)) {
           return false;
         }

src/classify/adaptmatch.cpp

@@ -1079,7 +1079,7 @@ void Classify::MasterMatcher(INT_TEMPLATES_STRUCT *templates, int16_t num_featur
   int top = blob_box.top();
   int bottom = blob_box.bottom();
   UnicharRating int_result;
-  for (auto result : results) {
+  for (auto &&result : results) {
     CLASS_ID class_id = result.Class;
     BIT_VECTOR protos = classes != nullptr ? classes[class_id]->PermProtos : AllProtosOn;
     BIT_VECTOR configs = classes != nullptr ? classes[class_id]->PermConfigs : AllConfigsOn;

src/classify/shapeclassifier.cpp

@@ -174,7 +174,7 @@ void ShapeClassifier::UnicharPrintResults(const char *context,
             GetUnicharset().id_to_unichar(result.unichar_id));
     if (!result.fonts.empty()) {
       tprintf(" Font Vector:");
-      for (auto font : result.fonts) {
+      for (auto &&font : result.fonts) {
         tprintf(" %d", font.fontinfo_id);
       }
     }

src/dict/dawg.h

@@ -382,7 +382,7 @@ class DawgPositionVector : public std::vector<DawgPosition> {
   /// true otherwise.
   inline bool add_unique(const DawgPosition &new_pos, bool debug,
                          const char *debug_msg) {
-    for (auto position : *this) {
+    for (auto &&position : *this) {
       if (position == new_pos) {
         return false;
       }

src/lstm/networkio.cpp

@@ -173,7 +173,7 @@ void NetworkIO::FromPixes(const StaticShape &shape, const std::vector<Image> &pi
   int target_height = shape.height();
   int target_width = shape.width();
   std::vector<std::pair<int, int>> h_w_pairs;
-  for (auto pix : pixes) {
+  for (auto &&pix : pixes) {
     Image var_pix = pix;
     int width = pixGetWidth(var_pix);
     if (target_width != 0) {

src/lstm/recodebeam.cpp

@@ -341,7 +341,7 @@ void RecodeBeamSearch::PrintBeam2(bool uids, int num_outputs,
   // fill the topology with depths first
   for (int step = beam.size() - 1; step >= 0; --step) {
     std::vector<tesseract::RecodePair> &heaps = beam.at(step)->beams_->heap();
-    for (auto node : heaps) {
+    for (auto &&node : heaps) {
       int backtracker = 0;
       const RecodeNode *curr = &node.data();
       while (curr != nullptr && !visited.count(curr)) {
@@ -426,7 +426,7 @@ void RecodeBeamSearch::extractSymbolChoices(const UNICHARSET *unicharset) {
     std::vector<const RecodeNode *> best_nodes;
     std::vector<const RecodeNode *> best;
     // Scan the segmented node chain for valid unichar ids.
-    for (auto entry : heaps) {
+    for (auto &&entry : heaps) {
       bool validChar = false;
       int backcounter = 0;
       const RecodeNode *node = &entry.data();

src/training/pango/pango_font_info.cpp

@@ -591,7 +591,7 @@ int FontUtils::FontScore(const std::unordered_map<char32, int64_t> &ch_map,
   }
   *raw_score = 0;
   int ok_chars = 0;
-  for (auto it : ch_map) {
+  for (auto &&it : ch_map) {
     bool covered =
         (coverage != nullptr) && (IsWhitespace(it.first) ||
                                   (pango_coverage_get(coverage, it.first) == PANGO_COVERAGE_EXACT));