From 263a22a67bf4ed55c37451c78d8563be96291fee Mon Sep 17 00:00:00 2001
From: Henry Weller <http://openfoam.org>
Date: Thu, 7 Nov 2019 17:17:09 +0000
Subject: [PATCH] subCycle: Add special treatment for nSubCycles = 1

Now running sub-cycling with nSubCycles = 1 is as efficient as running the same
code without the sub-cycling loop.
---
 src/OpenFOAM/algorithms/subCycle/subCycle.H | 93 +++++++++++++--------
 src/OpenFOAM/db/Time/subCycleTime.C         | 19 ++++-
 2 files changed, 75 insertions(+), 37 deletions(-)

diff --git a/src/OpenFOAM/algorithms/subCycle/subCycle.H b/src/OpenFOAM/algorithms/subCycle/subCycle.H
index 144274acd7..414a0f0e48 100644
--- a/src/OpenFOAM/algorithms/subCycle/subCycle.H
+++ b/src/OpenFOAM/algorithms/subCycle/subCycle.H
@@ -57,7 +57,7 @@ class subCycleField
         GeometricField& gf0_;
 
         //- Copy of the "real" old-time value of the field
-        GeometricField gf_0_;
+        tmp<GeometricField> gf_0_;
 
 
 public:
@@ -68,23 +68,35 @@ public:
     // Constructors
 
         //- Construct from field and number of sub-cycles
-        subCycleField(GeometricField& gf)
+        subCycleField
+        (
+            GeometricField& gf,
+            const label nSubCycles
+        )
         :
             gf_(gf),
-            gf0_(gf.oldTime()),
-            gf_0_(gf0_.name() + "_", gf0_)
-        {}
+            gf0_(gf.oldTime())
+        {
+            if (nSubCycles > 1)
+            {
+                gf_0_ = GeometricField::New(gf0_.name() + "_", gf0_);
+            }
+        }
 
 
     //- Destructor
     ~subCycleField()
     {
-        // Reset the old-time field
-        gf0_ = gf_0_;
+        if (gf_0_.valid())
+        {
+            // Reset the old-time field
+            gf0_ = gf_0_;
 
-        // Correct the time index of the field to correspond to the global time
-        gf_.timeIndex() = time().timeIndex();
-        gf0_.timeIndex() = time().timeIndex();
+            // Correct the time index of the field
+            // to correspond to the global time
+            gf_.timeIndex() = time().timeIndex();
+            gf0_.timeIndex() = time().timeIndex();
+        }
     }
 
     //- Access to time
@@ -136,25 +148,33 @@ public:
     // Constructors
 
         //- Construct from field list and number of sub-cycles
-        subCycleFields(List<GeometricField*>& gfPtrs)
+        subCycleFields
+        (
+            List<GeometricField*>& gfPtrs,
+            const label nSubCycles
+        )
         :
             gfPtrs_(gfPtrs),
-            gf0Ptrs_(gfPtrs.size()),
-            gf_0Ptrs_(gfPtrs.size())
+            gf0Ptrs_(gfPtrs.size())
         {
-            forAll(gfPtrs_, i)
+            if (nSubCycles > 1)
             {
-                gf0Ptrs_[i] = &gfPtrs_[i]->oldTime();
+                gf_0Ptrs_.setSize(gfPtrs.size());
 
-                gf_0Ptrs_.set
-                (
-                    i,
-                    new volScalarField
+                forAll(gfPtrs_, i)
+                {
+                    gf0Ptrs_[i] = &gfPtrs_[i]->oldTime();
+
+                    gf_0Ptrs_.set
                     (
-                        gf0Ptrs_[i]->name() + "_",
-                        *gf0Ptrs_[i]
-                    )
-                );
+                        i,
+                        new volScalarField
+                        (
+                            gf0Ptrs_[i]->name() + "_",
+                            *gf0Ptrs_[i]
+                        )
+                    );
+                }
             }
         }
 
@@ -162,15 +182,18 @@ public:
     //- Destructor
     ~subCycleFields()
     {
-        forAll(gfPtrs_, i)
+        if (gf_0Ptrs_.size())
         {
-            // Reset the old-time fields
-            *gf0Ptrs_[i] = gf_0Ptrs_[i];
+            forAll(gfPtrs_, i)
+            {
+                // Reset the old-time fields
+                *gf0Ptrs_[i] = gf_0Ptrs_[i];
 
-            // Correct the time index of the fields
-            // to correspond to the global time
-            gfPtrs_[i]->timeIndex() = time().timeIndex();
-            gf0Ptrs_[i]->timeIndex() = time().timeIndex();
+                // Correct the time index of the fields
+                // to correspond to the global time
+                gfPtrs_[i]->timeIndex() = time().timeIndex();
+                gf0Ptrs_[i]->timeIndex() = time().timeIndex();
+            }
         }
     }
 
@@ -223,11 +246,15 @@ public:
             const label nSubCycles
         )
         :
-            SubCycleField<GeometricField>(gf),
+            SubCycleField<GeometricField>(gf, nSubCycles),
             subCycleTime(const_cast<Time&>(this->time()), nSubCycles)
         {
-            // Update the field time index to correspond to the sub-cycle time
-            this->updateTimeIndex();
+            if (nSubCycles > 1)
+            {
+                // Update the field time index to correspond
+                // to the sub-cycle time
+                this->updateTimeIndex();
+            }
         }
 
         //- Disallow default bitwise copy construction
diff --git a/src/OpenFOAM/db/Time/subCycleTime.C b/src/OpenFOAM/db/Time/subCycleTime.C
index 7c4ad49058..ccbcb2ef28 100644
--- a/src/OpenFOAM/db/Time/subCycleTime.C
+++ b/src/OpenFOAM/db/Time/subCycleTime.C
@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     | Website:  https://openfoam.org
-    \\  /    A nd           | Copyright (C) 2011-2018 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2019 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -33,7 +33,10 @@ Foam::subCycleTime::subCycleTime(Time& t, const label nSubCycles)
     nSubCycles_(nSubCycles),
     subCycleIndex_(0)
 {
-    time_.subCycle(nSubCycles_);
+    if (nSubCycles_ > 1)
+    {
+        time_.subCycle(nSubCycles_);
+    }
 }
 
 
@@ -55,7 +58,10 @@ bool Foam::subCycleTime::end() const
 
 void Foam::subCycleTime::endSubCycle()
 {
-    time_.endSubCycle();
+    if (nSubCycles_ > 1)
+    {
+        time_.endSubCycle();
+    }
 }
 
 
@@ -63,8 +69,13 @@ void Foam::subCycleTime::endSubCycle()
 
 Foam::subCycleTime& Foam::subCycleTime::operator++()
 {
-    time_++;
+    if (nSubCycles_ > 1)
+    {
+        time_++;
+    }
+
     subCycleIndex_++;
+
     return *this;
 }