From 624f5d8181a449f36950503859271e1a052e8a65 Mon Sep 17 00:00:00 2001
From: "Claudius \"keldu\" Holeksa" <mail@keldu.de>
Date: Tue, 27 Jan 2026 09:17:33 +0100
Subject: Double free, but constexpr things compile now

---
 lib/core/c++/collision.hpp   | 34 +++++-----------------------------
 lib/core/c++/macroscopic.hpp | 25 +++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 29 deletions(-)

(limited to 'lib/core')

diff --git a/lib/core/c++/collision.hpp b/lib/core/c++/collision.hpp
index 2f20601..85c3af9 100644
--- a/lib/core/c++/collision.hpp
+++ b/lib/core/c++/collision.hpp
@@ -45,43 +45,19 @@ public:
 	 * Raw setup
 	 */
 	template<typename CellFieldSchema>
-	void apply(saw::data<CellFieldSchema, Encode>& field, saw::data<sch::FixedArray<sch::UInt64,Descriptor::D>> index, saw::data<sch::UInt64> time_step){
+	void apply(const saw::data<CellFieldSchema, Encode>& field, saw::data<sch::FixedArray<sch::UInt64,Descriptor::D>> index, saw::data<sch::UInt64> time_step) const {
 		bool is_even = ((time_step.get() % 2) == 0);
-		auto& cell = field.at(index);
 
-		auto& dfs_old = (is_even) ? cell.template get<"dfs_old">() : cell.template get<"dfs">();
-		// auto& dfs = (not is_even) ? cell.template get<"dfs_old">() : cell.template get<"dfs">();
+		// auto& dfs_f = (is_even) ? field.template get<"dfs">() : field.template get<"dfs_old">();
+		auto& dfs_old_f = (is_even) ? field.template get<"dfs_old">() : field.template get<"dfs">();
 
 		saw::data<T> rho;
 		saw::data<sch::FixedArray<T,Descriptor::D>> vel;
-		compute_rho_u<T,Descriptor>(dfs_old,rho,vel);
-		auto eq = equilibrium<T,Descriptor>(rho,vel);
-
-		for(uint64_t i = 0u; i < Descriptor::Q; ++i){
-			dfs_old({i}) = dfs_old({i}) + frequency_ * (eq.at(i) - dfs_old({i}));
-			// dfs_old({i}).set(dfs_old({i}).get() + (1.0 / relaxation_) * (eq.at(i).get() - dfs_old({i}).get()));
-		}
-	}
-
-	template<typename CellStructSchema>
-	void apply(
-		saw::data<CellStructSchema, Encode>* field, 
-		const saw::data<sch::FixedArray<sch::UInt64,Descriptor::D>>& meta,
-		const saw::data<sch::FixedArray<sch::UInt64,Descriptor::D>>& index,
-		saw::data<sch::UInt64> time_step
-	){
-		bool is_even = ((time_step.get() % 2) == 0);
-		auto& cell = field[0u];
-		
-		auto& dfs_old = (is_even) ? cell.template get<"dfs_old">() : cell.template get<"dfs">();
-
-		saw::data<T> rho;
-		saw::data<sch::FixedArray<T,Descriptor::D>> vel;
-		compute_rho_u<T,Descriptor>(dfs_old,rho,vel);
+		compute_rho_u<T,Descriptor>(dfs_old_f.at(index),rho,vel);
 		auto eq = equilibrium<T,Descriptor>(rho,vel);
 
 		for(uint64_t i = 0u; i < Descriptor::Q; ++i){
-			dfs_old({i}) = dfs_old({i}) + frequency_ * (eq.at(i) - dfs_old({i}));
+			dfs_old_f.at(index).at({i}) = dfs_old_f.at(index).at({i}) + frequency_ * (eq.at(i) - dfs_old_f.at(index).at({i}));
 		}
 	}
 };
diff --git a/lib/core/c++/macroscopic.hpp b/lib/core/c++/macroscopic.hpp
index 51368e9..1532873 100644
--- a/lib/core/c++/macroscopic.hpp
+++ b/lib/core/c++/macroscopic.hpp
@@ -4,6 +4,31 @@
 
 namespace kel {
 namespace lbm {
+template<typename T, typename Desc>
+void compute_rho_u (
+		const saw::data<sch::FixedArray<T,Desc::Q>>& dfs,
+		saw::data<T>& rho,
+		saw::data<sch::FixedArray<T,Desc::D>>& vel
+	)
+{
+	using dfi = df_info<T, Desc>;
+
+	rho = 0;
+	for(size_t j = 0; j < Desc::D; ++j){
+		vel.at({{j}}).set(0);
+	}
+
+	for(size_t j = 0; j < Desc::Q; ++j){
+		rho = rho + dfs.at({j});
+		for(size_t i = 0; i < Desc::D; ++i){
+			vel.at({{i}}) = vel.at({{i}}) + dfi::directions[j][i] * dfs.at({j}).get();
+		}
+	}
+
+	for(size_t i = 0; i < Desc::D; ++i){
+		vel.at({i}) = vel.at({i}) / rho;
+	}
+}
 /**
  * Calculate the macroscopic variables rho and u in Lattice Units.
  */
-- 
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