Use Reaction type hierarchy on C++ side

src/reaction.cpp

@@ -4,6 +4,9 @@
 #include <utility> // for move
 
 #include "hdf5_interface.h"
+#include "endf.h"
+#include "random_lcg.h"
+#include "secondary_uncorrelated.h"
 
 namespace openmc {
 
@@ -43,6 +46,116 @@ Reaction::Reaction(hid_t group, const std::vector<int>& temperatures)
       close_group(pgroup);
     }
   }
+
+  // <<<<<<<<<<<<<<<<<<<<<<<<<<<< REMOVE THIS <<<<<<<<<<<<<<<<<<<<<<<<<
+  // Before the secondary distribution refactor, when the angle/energy
+  // distribution was uncorrelated, no angle was actually sampled. With
+  // the refactor, an angle is always sampled for an uncorrelated
+  // distribution even when no angle distribution exists in the ACE file
+  // (isotropic is assumed). To preserve the RNG stream, we explicitly
+  // mark fission reactions so that we avoid the angle sampling.
+  if (is_fission(mt_)) {
+    for (auto& p : products_) {
+      if (p.particle_ == ParticleType::neutron) {
+        for (auto& d : p.distribution_) {
+          auto d_ = dynamic_cast<UncorrelatedAngleEnergy*>(d.get());
+          if (d_) d_->fission_ = true;
+        }
+      }
+    }
+  }
+  // <<<<<<<<<<<<<<<<<<<<<<<<<<<< REMOVE THIS <<<<<<<<<<<<<<<<<<<<<<<<<
 }
 
-}
+//==============================================================================
+// Fortran compatibility functions
+//==============================================================================
+
+Reaction* reaction_from_hdf5(hid_t group, int* temperatures, int n)
+{
+  std::vector<int> temps {temperatures, temperatures + n};
+  return new Reaction{group, temps};
+}
+
+void reaction_delete(Reaction* rx) { delete rx; }
+
+int reaction_mt(Reaction* rx) { return rx->mt_; }
+
+double reaction_q_value(Reaction* rx) { return rx->q_value_; }
+
+bool reaction_scatter_in_cm(Reaction* rx) { return rx->scatter_in_cm_; }
+
+double reaction_product_decay_rate(Reaction* rx, int product)
+{
+  return rx->products_[product - 1].decay_rate_;
+}
+
+int reaction_product_emission_mode(Reaction* rx, int product)
+{
+  switch (rx->products_[product - 1].emission_mode_) {
+  case ReactionProduct::EmissionMode::prompt:
+    return 1;
+  case ReactionProduct::EmissionMode::delayed:
+    return 2;
+  case ReactionProduct::EmissionMode::total:
+    return 3;
+  }
+}
+
+int reaction_product_particle(Reaction* rx, int product)
+{
+  switch (rx->products_[product - 1].particle_) {
+  case ParticleType::neutron:
+    return 1;
+  case ParticleType::photon:
+    return 2;
+  case ParticleType::electron:
+    return 3;
+  case ParticleType::positron:
+    return 4;
+  }
+}
+
+void reaction_product_sample(Reaction* rx, int product, double E_in, double* E_out, double* mu)
+{
+  rx->products_[product - 1].sample(E_in, *E_out, *mu);
+}
+
+double reaction_product_yield(Reaction* rx, int product, double E)
+{
+  return (*rx->products_[product - 1].yield_)(E);
+}
+
+int reaction_products_size(Reaction* rx) { return rx->products_.size(); }
+
+double reaction_xs(Reaction* rx, int temperature, int energy)
+{
+  return rx->xs_[temperature - 1].value[energy - 1];
+}
+
+double reaction_sample_elastic_mu(Reaction* rx, double E)
+{
+  // Get elastic scattering distribution
+  auto& d = rx->products_[0].distribution_[0];
+
+  // Check if it is an uncorrelated angle-energy distribution
+  auto d_ = dynamic_cast<UncorrelatedAngleEnergy*>(d.get());
+  if (d_) {
+    return d_->sampleMu(E);
+  } else {
+    return 2.0*prn() - 1.0;
+  }
+
+}
+
+int reaction_xs_size(Reaction* rx, int temperature)
+{
+  return rx->xs_[temperature - 1].value.size();
+}
+
+int reaction_xs_threshold(Reaction* rx, int temperature)
+{
+  return rx->xs_[temperature - 1].threshold;
+}
+
+}