From ac347708514d37ad05a72c659670f970bbe78f33 Mon Sep 17 00:00:00 2001
From: Hanno Spreeuw <h.spreeuw@esciencecenter.nl>
Date: Thu, 26 Feb 2026 13:07:00 +0100
Subject: [PATCH 01/12] Make "nj_max" readable outside Sapporo Light

The goal here is to make "nj_max" accessible at the level of the controlling Python script.
The approach is to add a Sapporo Light function that will return "nj_max", next add a PH4 function that can call this function and, subsequentlty, provide a Python interface to this function, i.e. a layered approach.
---
 lib/sapporo_light/sapporo.cpp | 16 ++++++++++++++++
 lib/sapporo_light/sapporo.h   |  2 ++
 src/amuse_ph4/interface.cc    | 10 ++++++++++
 src/amuse_ph4/interface.py    |  8 ++++++++
 4 files changed, 36 insertions(+)

diff --git a/lib/sapporo_light/sapporo.cpp b/lib/sapporo_light/sapporo.cpp
index 3ad6e5ab83..8136715760 100644
--- a/lib/sapporo_light/sapporo.cpp
+++ b/lib/sapporo_light/sapporo.cpp
@@ -270,3 +270,19 @@ int sapporo::get_ngb_list(int cluster_id,
     sort(nbl, nbl + min(nblen, maxlength));
     return overflow;
 }
+
+int sapporo::get_nj_max() const
+{
+    return nj_max;
+}
+
+extern "C" {
+
+int sapporo_get_nj_max(sapporo *s, int *value)
+{
+    if (!s) return -1;
+    *value = s->get_nj_max();
+    return 0;
+}
+
+}
\ No newline at end of file
diff --git a/lib/sapporo_light/sapporo.h b/lib/sapporo_light/sapporo.h
index cb8b60ce59..ed0a9fcad6 100644
--- a/lib/sapporo_light/sapporo.h
+++ b/lib/sapporo_light/sapporo.h
@@ -182,8 +182,10 @@ class sapporo {
     device.acc_i = NULL;
     device.vel_i = NULL;
     device.jrk_i = NULL;
+
     
   };
+  int get_nj_max() const;
   ~sapporo() {};
   
   int open(int cluster_id);
diff --git a/src/amuse_ph4/interface.cc b/src/amuse_ph4/interface.cc
index 970b9f4409..f1f6a9b192 100644
--- a/src/amuse_ph4/interface.cc
+++ b/src/amuse_ph4/interface.cc
@@ -936,3 +936,13 @@ int get_id_of_updated_particle(int index, int * index_of_particle, int * status)
     *status = jd->UpdatedParticles[index].status;
     return 0;
 }
+
+extern "C" {
+    int sapporo_get_nj_max(int *value);
+}
+
+int get_nj_max(int *value)
+{
+    if (!jd) return -1;
+    return sapporo_get_nj_max(value);
+}
diff --git a/src/amuse_ph4/interface.py b/src/amuse_ph4/interface.py
index 0c9f26062c..6f8e784d84 100644
--- a/src/amuse_ph4/interface.py
+++ b/src/amuse_ph4/interface.py
@@ -464,6 +464,14 @@ def recompute_timesteps():
         function.result_type = 'int32'
         return function
 
+    def get_nj_max(self):
+        """
+        Returns the maximum number of particles supported by Sapporo Light.
+        """
+        function = LegacyFunctionSpecification()
+        return function(
+            returns=int,
+        )
 
 class ph4(GravitationalDynamics,GravityFieldCode):
 

From 9c465b5d4242781c89d1c4edc69e7e5f63e2b3c3 Mon Sep 17 00:00:00 2001
From: HannoSpreeuw <h.spreeuw@esciencecenter.nl>
Date: Wed, 4 Mar 2026 11:09:28 +0100
Subject: [PATCH 02/12] This code should not be needed.

According to the AMUSE guideline https://amuse.readthedocs.io/en/latest/tutorial/legacy_code.html we should be able to leave "src/amuse_ph4/interface.cc" untouched, i.e. exactly the same as in the "main" branch.
I.e., this code should not be necessary.
---
 src/amuse_ph4/interface.cc | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/src/amuse_ph4/interface.cc b/src/amuse_ph4/interface.cc
index f1f6a9b192..9fe8462479 100644
--- a/src/amuse_ph4/interface.cc
+++ b/src/amuse_ph4/interface.cc
@@ -935,14 +935,4 @@ int get_id_of_updated_particle(int index, int * index_of_particle, int * status)
     *index_of_particle = jd->UpdatedParticles[index].index_of_particle;
     *status = jd->UpdatedParticles[index].status;
     return 0;
-}
-
-extern "C" {
-    int sapporo_get_nj_max(int *value);
-}
-
-int get_nj_max(int *value)
-{
-    if (!jd) return -1;
-    return sapporo_get_nj_max(value);
-}
+ }

From d868f8a4a0204b10e5553b1b09e788b9277eb615 Mon Sep 17 00:00:00 2001
From: HannoSpreeuw <h.spreeuw@esciencecenter.nl>
Date: Wed, 4 Mar 2026 11:14:16 +0100
Subject: [PATCH 03/12] Added space

---
 src/amuse_ph4/interface.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/amuse_ph4/interface.cc b/src/amuse_ph4/interface.cc
index 9fe8462479..f964ac0d0f 100644
--- a/src/amuse_ph4/interface.cc
+++ b/src/amuse_ph4/interface.cc
@@ -935,4 +935,4 @@ int get_id_of_updated_particle(int index, int * index_of_particle, int * status)
     *index_of_particle = jd->UpdatedParticles[index].index_of_particle;
     *status = jd->UpdatedParticles[index].status;
     return 0;
- }
+ }
\ No newline at end of file

From 07a18207308c8c751646c3b466d871d0103e39f3 Mon Sep 17 00:00:00 2001
From: HannoSpreeuw <h.spreeuw@esciencecenter.nl>
Date: Wed, 4 Mar 2026 11:16:06 +0100
Subject: [PATCH 04/12] Make "interface.cc" exactly the same as in "main"

---
 src/amuse_ph4/interface.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/amuse_ph4/interface.cc b/src/amuse_ph4/interface.cc
index f964ac0d0f..970b9f4409 100644
--- a/src/amuse_ph4/interface.cc
+++ b/src/amuse_ph4/interface.cc
@@ -935,4 +935,4 @@ int get_id_of_updated_particle(int index, int * index_of_particle, int * status)
     *index_of_particle = jd->UpdatedParticles[index].index_of_particle;
     *status = jd->UpdatedParticles[index].status;
     return 0;
- }
\ No newline at end of file
+}

From 7c9bb6385a89ec13a2044d76a493a441d55a27d0 Mon Sep 17 00:00:00 2001
From: HannoSpreeuw <h.spreeuw@esciencecenter.nl>
Date: Fri, 6 Mar 2026 10:37:59 +0100
Subject: [PATCH 05/12] Move "get_nj_max" to "sapporoG6lib.cpp"

In "sapporoG6lib.cpp" we can do "return grav.get_nj_max()" since that has "sapporo grav;".
---
 lib/sapporo_light/sapporo.cpp      | 11 -----------
 lib/sapporo_light/sapporo.h        | 12 +++++++++++-
 lib/sapporo_light/sapporoG6lib.cpp |  6 ++++++
 3 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/lib/sapporo_light/sapporo.cpp b/lib/sapporo_light/sapporo.cpp
index 8136715760..1afd0c1c4e 100644
--- a/lib/sapporo_light/sapporo.cpp
+++ b/lib/sapporo_light/sapporo.cpp
@@ -275,14 +275,3 @@ int sapporo::get_nj_max() const
 {
     return nj_max;
 }
-
-extern "C" {
-
-int sapporo_get_nj_max(sapporo *s, int *value)
-{
-    if (!s) return -1;
-    *value = s->get_nj_max();
-    return 0;
-}
-
-}
\ No newline at end of file
diff --git a/lib/sapporo_light/sapporo.h b/lib/sapporo_light/sapporo.h
index ed0a9fcad6..73ecd4f1ff 100644
--- a/lib/sapporo_light/sapporo.h
+++ b/lib/sapporo_light/sapporo.h
@@ -169,7 +169,7 @@ class sapporo {
 
     predict = false;
     nj_modified = 0;
-    
+
     device.address_j = NULL;
 
     device.t_j   = NULL;
@@ -232,3 +232,13 @@ class sapporo {
 };
 
 #endif 
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+int g6_get_nj_max_();
+
+#ifdef __cplusplus
+}
+#endif
\ No newline at end of file
diff --git a/lib/sapporo_light/sapporoG6lib.cpp b/lib/sapporo_light/sapporoG6lib.cpp
index 3aff64394f..37ad6692fd 100644
--- a/lib/sapporo_light/sapporoG6lib.cpp
+++ b/lib/sapporo_light/sapporoG6lib.cpp
@@ -81,3 +81,9 @@ extern "C" {
 
 }
 
+extern "C" {
+    int g6_get_nj_max_() {
+        return grav.get_nj_max();
+    }
+}
+

From fdf0468a9a579c59b6b189216f94c27a987ff006 Mon Sep 17 00:00:00 2001
From: HannoSpreeuw <h.spreeuw@esciencecenter.nl>
Date: Fri, 6 Mar 2026 10:52:36 +0100
Subject: [PATCH 06/12] This compiles, but does not run

This compiles, i.e.
"./setup install sapporo_light" and "./setup install amuse-ph4" will complete without error.
However, Erwan's script with an additional "print(f"{code.get_nj_max() = }, ")" will yield
"
TypeError: ph4Interface.get_nj_max() takes 0 positional arguments but 1 was given
"
---
 src/amuse_ph4/interface.cc |  7 +++++++
 src/amuse_ph4/interface.py | 10 +++-------
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/src/amuse_ph4/interface.cc b/src/amuse_ph4/interface.cc
index 970b9f4409..9efaced7a7 100644
--- a/src/amuse_ph4/interface.cc
+++ b/src/amuse_ph4/interface.cc
@@ -936,3 +936,10 @@ int get_id_of_updated_particle(int index, int * index_of_particle, int * status)
     *status = jd->UpdatedParticles[index].status;
     return 0;
 }
+
+extern "C" int g6_get_nj_max_();
+
+int get_nj_max()
+{
+    return g6_get_nj_max_();
+}
\ No newline at end of file
diff --git a/src/amuse_ph4/interface.py b/src/amuse_ph4/interface.py
index 6f8e784d84..c1675660c5 100644
--- a/src/amuse_ph4/interface.py
+++ b/src/amuse_ph4/interface.py
@@ -464,14 +464,10 @@ def recompute_timesteps():
         function.result_type = 'int32'
         return function
 
-    def get_nj_max(self):
-        """
-        Returns the maximum number of particles supported by Sapporo Light.
-        """
+    def get_nj_max():
         function = LegacyFunctionSpecification()
-        return function(
-            returns=int,
-        )
+        function.result_type = 'int32'
+        return function
 
 class ph4(GravitationalDynamics,GravityFieldCode):
 

From a10558bbad3060a992147255ec7056f85128baee Mon Sep 17 00:00:00 2001
From: HannoSpreeuw <h.spreeuw@esciencecenter.nl>
Date: Wed, 11 Mar 2026 20:06:17 +0100
Subject: [PATCH 07/12] This function definition need not be separate

This function definition does not need to be separated.
---
 lib/sapporo_light/sapporoG6lib.cpp | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/lib/sapporo_light/sapporoG6lib.cpp b/lib/sapporo_light/sapporoG6lib.cpp
index 37ad6692fd..c4c4481949 100644
--- a/lib/sapporo_light/sapporoG6lib.cpp
+++ b/lib/sapporo_light/sapporoG6lib.cpp
@@ -49,6 +49,9 @@ extern "C" {
     return grav.calc_lasthalf2(*cluster_id, *nj, *ni,
 			       index, xi, vi, *eps2, h2, acc, jerk, pot, inn);
   }
+  int g6_get_nj_max_() {
+    return grav.get_nj_max();
+  }
   
   int g6_initialize_jp_buffer_(int* cluster_id, int* buf_size) {return 0;}
   int g6_flush_jp_buffer_(int* cluster_id) {return 0;}
@@ -80,10 +83,3 @@ extern "C" {
 			     
 
 }
-
-extern "C" {
-    int g6_get_nj_max_() {
-        return grav.get_nj_max();
-    }
-}
-

From f8feb3968738d2d3e3f494dcfd04fd3131c57e4b Mon Sep 17 00:00:00 2001
From: HannoSpreeuw <h.spreeuw@esciencecenter.nl>
Date: Wed, 11 Mar 2026 20:10:03 +0100
Subject: [PATCH 08/12] 'extern "C"' not needed here

1) 'extern "C"' not needed here
2) We need to adhere to AMUSE standards, I guess the legacy decorator implies that we need to set an argument 'int * value' and '*value = jd->get_nj_max(); return 0;' or we will be returned an empty list instead of an integer.
3) As a consequence of 2) we need to add an argument to the function: 'function.addParameter(...'.
---
 src/amuse_ph4/interface.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/amuse_ph4/interface.py b/src/amuse_ph4/interface.py
index c1675660c5..dca15222bf 100644
--- a/src/amuse_ph4/interface.py
+++ b/src/amuse_ph4/interface.py
@@ -464,8 +464,11 @@ def recompute_timesteps():
         function.result_type = 'int32'
         return function
 
+    @legacy_function
     def get_nj_max():
         function = LegacyFunctionSpecification()
+        function.addParameter('nj_max', dtype='int32',
+                              direction=function.OUT)
         function.result_type = 'int32'
         return function
 

From 3321825b9e899991978bc9c778b5faad6d52d106 Mon Sep 17 00:00:00 2001
From: HannoSpreeuw <h.spreeuw@esciencecenter.nl>
Date: Wed, 11 Mar 2026 20:21:44 +0100
Subject: [PATCH 09/12] "interface.cc" should have been added

"interface.cc" should have been added as part of the previous commit.
---
 src/amuse_ph4/interface.cc | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/src/amuse_ph4/interface.cc b/src/amuse_ph4/interface.cc
index 9efaced7a7..7357091895 100644
--- a/src/amuse_ph4/interface.cc
+++ b/src/amuse_ph4/interface.cc
@@ -937,9 +937,8 @@ int get_id_of_updated_particle(int index, int * index_of_particle, int * status)
     return 0;
 }
 
-extern "C" int g6_get_nj_max_();
-
-int get_nj_max()
+int get_nj_max(int * value)
 {
-    return g6_get_nj_max_();
-}
\ No newline at end of file
+  *value = jd->get_nj_max();
+  return 0;
+}

From c65f686b9a1f7400ccd2104381752bf7971ec7f4 Mon Sep 17 00:00:00 2001
From: HannoSpreeuw <h.spreeuw@esciencecenter.nl>
Date: Wed, 11 Mar 2026 20:28:44 +0100
Subject: [PATCH 10/12] Prototype and implementation of jdata::get_nj_max.

Essential is the '#ifdef GPU', since, when one executes "./setup install amuse-ph4" one will not link with Sapporo as one would when executing "./setup install amuse-ph4-sapporo".
So "GPU" and "Sapporo" go hand in hand and one needs to make sure that "./setup install amuse-ph4" will complete without error when no GPU is available.
---
 src/amuse_ph4/src/jdata.cc | 10 ++++++++++
 src/amuse_ph4/src/jdata.h  |  1 +
 2 files changed, 11 insertions(+)

diff --git a/src/amuse_ph4/src/jdata.cc b/src/amuse_ph4/src/jdata.cc
index f5530ee36a..2b48614eb6 100644
--- a/src/amuse_ph4/src/jdata.cc
+++ b/src/amuse_ph4/src/jdata.cc
@@ -34,6 +34,7 @@
 
 #ifdef GPU
 #include "grape.h"
+#include "sapporo.h"
 #endif
 
 // AMUSE STOPPING CONDITIONS SUPPORT
@@ -1153,3 +1154,12 @@ real jdata::get_tnext()
     int ndum;
     return sched->get_list(NULL, ndum);
 }
+
+int jdata::get_nj_max()
+{
+#ifdef GPU
+    return g6_get_nj_max_();
+#else
+    return 0;
+#endif
+}
diff --git a/src/amuse_ph4/src/jdata.h b/src/amuse_ph4/src/jdata.h
index 9ec464dfb7..069bd57095 100644
--- a/src/amuse_ph4/src/jdata.h
+++ b/src/amuse_ph4/src/jdata.h
@@ -212,6 +212,7 @@ class jdata {
     void spec_output(const char *s = NULL);
     void to_com();
     real get_tnext();
+    int get_nj_max();
 
     // In gpu.cc:
 

From e71a85a4dbe82e6fe28e5c85781f51a28d39522d Mon Sep 17 00:00:00 2001
From: Hanno Spreeuw <h.spreeuw@esciencecenter.nl>
Date: Thu, 12 Mar 2026 16:51:47 +0100
Subject: [PATCH 11/12] Things will go wrong when there's a header include loop

Following@LourensVeen recommendation to prevent things from going wrong when there's a header include loop.
---
 lib/sapporo_light/sapporo.h | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/lib/sapporo_light/sapporo.h b/lib/sapporo_light/sapporo.h
index 73ecd4f1ff..1a2469e8ef 100644
--- a/lib/sapporo_light/sapporo.h
+++ b/lib/sapporo_light/sapporo.h
@@ -103,6 +103,9 @@ extern "C"
 {
   int  get_device_count();
   cudaError_t host_evaluate_gravity(sapporo_multi_struct);
+#ifdef __cplusplus
+  int g6_get_nj_max_();
+#endif
 }
 
 class sapporo {
@@ -185,12 +188,12 @@ class sapporo {
 
     
   };
-  int get_nj_max() const;
   ~sapporo() {};
   
   int open(int cluster_id);
   int close(int cluster_id);
   int get_n_pipes();
+  int get_nj_max() const;
   int set_ti(int cluster_id, double ti);
 
   int set_j_particle(int cluster_id,
@@ -232,13 +235,3 @@ class sapporo {
 };
 
 #endif 
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-int g6_get_nj_max_();
-
-#ifdef __cplusplus
-}
-#endif
\ No newline at end of file

From dd08d1f38c8bbd031894c2e6ce55d42d469d92d5 Mon Sep 17 00:00:00 2001
From: Hanno Spreeuw <h.spreeuw@esciencecenter.nl>
Date: Thu, 12 Mar 2026 16:55:34 +0100
Subject: [PATCH 12/12] Accommodate CPU users

Following @LourensVeen's recommendation: When running PH4 simulations on a CPU instead of a GPU, Sapporo Light's "nj_max" does not play a role, so one will want to return a different very large number indicating the maximum number of stars allowed for the simulation. In case the number of stars in a simulation running on a CPU will approach "nj_max = std::numeric_limits<int>::max();" one will probably run into a memory error, but that's another matter.
---
 src/amuse_ph4/src/jdata.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/amuse_ph4/src/jdata.cc b/src/amuse_ph4/src/jdata.cc
index 2b48614eb6..9acef22d21 100644
--- a/src/amuse_ph4/src/jdata.cc
+++ b/src/amuse_ph4/src/jdata.cc
@@ -1160,6 +1160,6 @@ int jdata::get_nj_max()
 #ifdef GPU
     return g6_get_nj_max_();
 #else
-    return 0;
+    return std::numeric_limits<int>::max();
 #endif
 }