From 16392c85288c24b5baaddadfda93fc25970c168f Mon Sep 17 00:00:00 2001
From: Nikolas <niko.wittek@gmail.com>
Date: Fri, 6 Sep 2024 15:03:30 +0200
Subject: [PATCH] Fix size_t underflow in geodesic worldtube evolution

---
 .../Worldtube/ElementActions/SendToWorldtube.hpp              | 4 ++--
 .../Worldtube/SingletonActions/ReceiveElementData.hpp         | 4 ++--
 .../Worldtube/ElementActions/Test_Iterations.cpp              | 3 ++-
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/Evolution/Systems/CurvedScalarWave/Worldtube/ElementActions/SendToWorldtube.hpp b/src/Evolution/Systems/CurvedScalarWave/Worldtube/ElementActions/SendToWorldtube.hpp
index 129eca3ddee2..6d860b72ee82 100644
--- a/src/Evolution/Systems/CurvedScalarWave/Worldtube/ElementActions/SendToWorldtube.hpp
+++ b/src/Evolution/Systems/CurvedScalarWave/Worldtube/ElementActions/SendToWorldtube.hpp
@@ -164,8 +164,8 @@ struct SendToWorldtube {
     Parallel::receive_data<Worldtube::Tags::SphericalHarmonicsInbox<Dim>>(
         worldtube_component, db::get<::Tags::TimeStepId>(box),
         std::make_pair(element_id, std::move(Ylm_coefs)));
-    if (db::get<Tags::CurrentIteration>(box) <
-        db::get<Tags::MaxIterations>(box) - 1) {
+    if (db::get<Tags::CurrentIteration>(box) + 1 <
+        db::get<Tags::MaxIterations>(box) ) {
       db::mutate<Tags::CurrentIteration>(
           [](const gsl::not_null<size_t*> current_iteration) {
             *current_iteration += 1;
diff --git a/src/Evolution/Systems/CurvedScalarWave/Worldtube/SingletonActions/ReceiveElementData.hpp b/src/Evolution/Systems/CurvedScalarWave/Worldtube/SingletonActions/ReceiveElementData.hpp
index 752f5f49963f..5c228a52cced 100644
--- a/src/Evolution/Systems/CurvedScalarWave/Worldtube/SingletonActions/ReceiveElementData.hpp
+++ b/src/Evolution/Systems/CurvedScalarWave/Worldtube/SingletonActions/ReceiveElementData.hpp
@@ -128,8 +128,8 @@ struct ReceiveElementData {
         ylm::ylm_to_stf_0(dt_psi_ylm_l0), std::move(psi_stf_l1),
         std::move(dt_psi_stf_l1));
     inbox.erase(time_step_id);
-    if (db::get<Tags::CurrentIteration>(box) <
-        db::get<Tags::MaxIterations>(box) - 1) {
+    if (db::get<Tags::CurrentIteration>(box) + 1 <
+        db::get<Tags::MaxIterations>(box)) {
       db::mutate<Tags::CurrentIteration>(
           [](const gsl::not_null<size_t*> current_iteration) {
             *current_iteration += 1;
diff --git a/tests/Unit/Evolution/Systems/CurvedScalarWave/Worldtube/ElementActions/Test_Iterations.cpp b/tests/Unit/Evolution/Systems/CurvedScalarWave/Worldtube/ElementActions/Test_Iterations.cpp
index d1c6644ac485..0c22153666e3 100644
--- a/tests/Unit/Evolution/Systems/CurvedScalarWave/Worldtube/ElementActions/Test_Iterations.cpp
+++ b/tests/Unit/Evolution/Systems/CurvedScalarWave/Worldtube/ElementActions/Test_Iterations.cpp
@@ -296,7 +296,7 @@ void test_iterations(const size_t max_iterations) {
           make_not_null(&runner), element_id));
     }
 
-    for (size_t current_iteration = 1; current_iteration <= max_iterations - 1;
+    for (size_t current_iteration = 1; current_iteration + 1 <= max_iterations;
          ++current_iteration) {
       CAPTURE(current_iteration);
       using inbox_tag = Tags::SphericalHarmonicsInbox<Dim>;
@@ -411,6 +411,7 @@ void test_iterations(const size_t max_iterations) {
 }
 
 SPECTRE_TEST_CASE("Unit.CurvedScalarWave.Worldtube.Iterations", "[Unit]") {
+  test_iterations(0);
   test_iterations(1);
   test_iterations(2);
   test_iterations(5);