From 752fb9507f54f5a771502539d9a281f407903b10 Mon Sep 17 00:00:00 2001
From: Andre Gaschler <gaschlera@gmail.com>
Date: Wed, 2 Jan 2019 13:57:02 +0100
Subject: [PATCH] Use efficient string concatenation (#1488)

std::string::operator+ is very inefficient
---
 cartographer/common/histogram.cc              | 19 +++++++++----------
 cartographer/io/xray_points_processor.cc      |  3 ++-
 .../sensor/internal/trajectory_collator.cc    |  8 +++++---
 3 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/cartographer/common/histogram.cc b/cartographer/common/histogram.cc
index 4a1cd84..e887208 100644
--- a/cartographer/common/histogram.cc
+++ b/cartographer/common/histogram.cc
@@ -20,6 +20,7 @@
 #include <numeric>
 #include <string>
 
+#include "absl/strings/str_cat.h"
 #include "cartographer/common/port.h"
 #include "glog/logging.h"
 
@@ -37,10 +38,8 @@ std::string Histogram::ToString(const int buckets) const {
   const float max = *std::max_element(values_.begin(), values_.end());
   const float mean =
       std::accumulate(values_.begin(), values_.end(), 0.f) / values_.size();
-  std::string result = "Count: " + std::to_string(values_.size()) +
-                       "  Min: " + std::to_string(min) +
-                       "  Max: " + std::to_string(max) +
-                       "  Mean: " + std::to_string(mean);
+  std::string result = absl::StrCat("Count: ", values_.size(), "  Min: ", min,
+                                    "  Max: ", max, "  Mean: ", mean);
   if (min == max) {
     return result;
   }
@@ -60,8 +59,8 @@ std::string Histogram::ToString(const int buckets) const {
       }
     }
     total_count += count;
-    result += "\n[" + std::to_string(lower_bound) + ", " +
-              std::to_string(upper_bound) + ((i + 1 == buckets) ? "]" : ")");
+    absl::StrAppend(&result, "\n[", lower_bound, ", ", upper_bound,
+                    i + 1 == buckets ? "]" : ")");
     constexpr int kMaxBarChars = 20;
     const int bar =
         (count * kMaxBarChars + values_.size() / 2) / values_.size();
@@ -69,10 +68,10 @@ std::string Histogram::ToString(const int buckets) const {
     for (int i = 0; i != kMaxBarChars; ++i) {
       result += (i < (kMaxBarChars - bar)) ? " " : "#";
     }
-    result += "\tCount: " + std::to_string(count) + " (" +
-              std::to_string(count * 1e2f / values_.size()) + "%)";
-    result += "\tTotal: " + std::to_string(total_count) + " (" +
-              std::to_string(total_count * 1e2f / values_.size()) + "%)";
+    absl::StrAppend(&result, "\tCount: ", count, " (",
+                    count * 1e2f / values_.size(), "%)",
+                    "\tTotal: ", total_count, " (",
+                    total_count * 1e2f / values_.size(), "%)");
     lower_bound = upper_bound;
   }
   return result;
diff --git a/cartographer/io/xray_points_processor.cc b/cartographer/io/xray_points_processor.cc
index 4e16655..856403c 100644
--- a/cartographer/io/xray_points_processor.cc
+++ b/cartographer/io/xray_points_processor.cc
@@ -21,6 +21,7 @@
 
 #include "Eigen/Core"
 #include "absl/memory/memory.h"
+#include "absl/strings/str_cat.h"
 #include "cartographer/common/lua_parameter_dictionary.h"
 #include "cartographer/common/math.h"
 #include "cartographer/io/draw_trajectories.h"
@@ -236,7 +237,7 @@ PointsProcessor::FlushResult XRayPointsProcessor::Flush() {
     for (size_t i = 0; i < floors_.size(); ++i) {
       WriteVoxels(
           aggregations_[i],
-          file_writer_factory_(output_filename_ + std::to_string(i) + ".png")
+          file_writer_factory_(absl::StrCat(output_filename_, i, ".png"))
               .get());
     }
   }
diff --git a/cartographer/sensor/internal/trajectory_collator.cc b/cartographer/sensor/internal/trajectory_collator.cc
index 982dbbd..02d2b51 100644
--- a/cartographer/sensor/internal/trajectory_collator.cc
+++ b/cartographer/sensor/internal/trajectory_collator.cc
@@ -16,6 +16,8 @@
 
 #include "cartographer/sensor/internal/trajectory_collator.h"
 
+#include "absl/strings/str_cat.h"
+
 namespace cartographer {
 namespace sensor {
 
@@ -71,7 +73,8 @@ void TrajectoryCollator::RegisterMetrics(
 
 metrics::Counter* TrajectoryCollator::GetOrCreateSensorMetric(
     const std::string& sensor_id, int trajectory_id) {
-  const std::string map_key = sensor_id + "/" + std::to_string(trajectory_id);
+  const std::string trajectory_id_str = absl::StrCat(trajectory_id);
+  const std::string map_key = absl::StrCat(sensor_id, "/", trajectory_id_str);
 
   auto metrics_map_itr = metrics_map_.find(map_key);
   if (metrics_map_itr != metrics_map_.end()) {
@@ -80,8 +83,7 @@ metrics::Counter* TrajectoryCollator::GetOrCreateSensorMetric(
 
   LOG(INFO) << "Create metrics handler for key: " << map_key;
   auto new_counter = collator_metrics_family_->Add(
-      {{"sensor_id", sensor_id},
-       {"trajectory_id", std::to_string(trajectory_id)}});
+      {{"sensor_id", sensor_id}, {"trajectory_id", trajectory_id_str}});
 
   metrics_map_[map_key] = new_counter;
   return new_counter;