From a60cca4a43358b09bcc351e42dc3dca858c5e378 Mon Sep 17 00:00:00 2001
From: damienrg <damienrg@users.noreply.github.com>
Date: Thu, 7 Mar 2019 11:56:01 +0100
Subject: [PATCH] Refactor number of cells magic number (#1522)

---
 cartographer/mapping/probability_values.cc | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/cartographer/mapping/probability_values.cc b/cartographer/mapping/probability_values.cc
index a30f96e..9ce7839 100644
--- a/cartographer/mapping/probability_values.cc
+++ b/cartographer/mapping/probability_values.cc
@@ -23,14 +23,16 @@ namespace mapping {
 
 namespace {
 
+constexpr int kNumberOfValues = 32768;
+
 // 0 is unknown, [1, 32767] maps to [lower_bound, upper_bound].
 float SlowValueToBoundedFloat(const uint16 value, const uint16 unknown_value,
                               const float unknown_result,
                               const float lower_bound,
                               const float upper_bound) {
-  CHECK_LE(value, 32767);
+  CHECK_LT(value, kNumberOfValues);
   if (value == unknown_value) return unknown_result;
-  const float kScale = (upper_bound - lower_bound) / 32766.f;
+  const float kScale = (upper_bound - lower_bound) / (kNumberOfValues - 2.f);
   return value * kScale + (lower_bound - kScale);
 }
 
@@ -41,7 +43,7 @@ std::unique_ptr<std::vector<float>> PrecomputeValueToBoundedFloat(
   // Repeat two times, so that both values with and without the update marker
   // can be converted to a probability.
   for (int repeat = 0; repeat != 2; ++repeat) {
-    for (int value = 0; value != 32768; ++value) {
+    for (int value = 0; value != kNumberOfValues; ++value) {
       result->push_back(SlowValueToBoundedFloat(
           value, unknown_value, unknown_result, lower_bound, upper_bound));
     }
@@ -73,7 +75,7 @@ std::vector<uint16> ComputeLookupTableToApplyOdds(const float odds) {
   std::vector<uint16> result;
   result.push_back(ProbabilityToValue(ProbabilityFromOdds(odds)) +
                    kUpdateMarker);
-  for (int cell = 1; cell != 32768; ++cell) {
+  for (int cell = 1; cell != kNumberOfValues; ++cell) {
     result.push_back(ProbabilityToValue(ProbabilityFromOdds(
                          odds * Odds((*kValueToProbability)[cell]))) +
                      kUpdateMarker);
@@ -87,7 +89,7 @@ std::vector<uint16> ComputeLookupTableToApplyCorrespondenceCostOdds(
   result.push_back(CorrespondenceCostToValue(ProbabilityToCorrespondenceCost(
                        ProbabilityFromOdds(odds))) +
                    kUpdateMarker);
-  for (int cell = 1; cell != 32768; ++cell) {
+  for (int cell = 1; cell != kNumberOfValues; ++cell) {
     result.push_back(
         CorrespondenceCostToValue(
             ProbabilityToCorrespondenceCost(ProbabilityFromOdds(