fix 32-bit usage of size_t

On 32-bit systems size_t is identical unsigned in, causing
redefinition errors in tables (Array_I_S).

This patch guards against the 32-bit redefinition and defines
Array_I_S = Array_I_U for the python interface if not already defined.

Applies debian patch size_t_int32.patch
https://salsa.debian.org/science-team/netgen/-/blob/d7ca1c564d90d00ce3d83e0b63c36fbec11cf1ce/debian/patches/size_t_int32.patch

Fixes NGSolve#168

Author: drew-parsons

libsrc/core/python_ngcore.hpp

@@ -2,6 +2,7 @@
 #define NETGEN_CORE_PYTHON_NGCORE_HPP
 
 #include "ngcore_api.hpp" // for operator new
+#include <cstdint>
 #include <pybind11/pybind11.h>
 #include <pybind11/operators.h>
 #include <pybind11/numpy.h>
@@ -182,10 +183,12 @@ namespace ngcore
     static std::string GetName() { return "D"; }
   };
 
+#if INTPTR_MAX != INT32_MAX
   template<>
   struct PyNameTraits<size_t> {
     static std::string GetName() { return "S"; }
   };
+#endif
 
   template<typename T>
   struct PyNameTraits<std::shared_ptr<T>> {

libsrc/core/python_ngcore_export.cpp

@@ -1,3 +1,5 @@
+#include <cstdint>
+
 #include "python_ngcore.hpp"
 #include "bitarray.hpp"
 #include "taskmanager.hpp"
@@ -23,7 +25,9 @@ PYBIND11_MODULE(pyngcore, m) // NOLINT
   catch(...) {}
   ExportArray<int>(m);
   ExportArray<unsigned>(m);
+#if INTPTR_MAX != INT32_MAX
   ExportArray<size_t>(m);
+#endif
   ExportArray<double>(m);
   ExportArray<float>(m);
   ExportArray<signed short>(m);

libsrc/core/table.hpp

@@ -8,6 +8,7 @@
 /**************************************************************************/
 
 #include <atomic>
+#include <cstdint>
 #include <iostream>
 #include <optional>
 
@@ -104,8 +105,10 @@ namespace ngcore
   { return TablePrefixSum32 (FlatArray<unsigned> (entrysize.Size(), (unsigned int*)(int*)(entrysize.Addr(0)))); }
   NETGEN_INLINE size_t * TablePrefixSum (FlatArray<std::atomic<int>> entrysize)
   { return TablePrefixSum32 (FlatArray<unsigned> (entrysize.Size(), (unsigned int*)(std::atomic<int>*)entrysize.Addr(0))); }
+#if INTPTR_MAX != INT32_MAX
   NETGEN_INLINE size_t * TablePrefixSum (FlatArray<size_t> entrysize)
   { return TablePrefixSum64 (entrysize); }
+#endif
 
 
   /**

python/pyngcore/__init__.py

@@ -1 +1,7 @@
 from .pyngcore import *
+
+# <size_t> is the same as <unsigned int> on 32 bit arches
+# in which case Array_I_S is not defined by python_ngcore_export.cpp.
+# In this case identify it with Array_I_U.
+try: Array_I_S
+except NameError: Array_I_S=Array_I_U