ENH: improve flexibilty of globalIndex

- construct or reset from a list of local sizes. It is generally
  easier and safer to assemble sizes and let globalIndex determine the
  corresponding offsets, when working with raw values.

- Can use reset() from sizes or fine-tune offsets with setLocalSize()
  instead of using the potentially more fragile non-const access to
  the offsets.

- add globalIndex const_iterator to iterate across the access ranges.
  This is makes it simpler to use with the List slice() method to
  access or operate on a sub-section of list.

  For example,
      scalarField allValues = ...;
      globalIndex procAccess = ...;

      for (const labelRange& range : procAccess)
      {
          someOutput(allValues.slice(range));
      }

src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndex.C

@@ -27,6 +27,84 @@ License
 \*---------------------------------------------------------------------------*/
 
 #include "globalIndex.H"
+#include "labelRange.H"
+
+// * * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * //
+
+Foam::labelList
+Foam::globalIndex::calcOffsets
+(
+    const labelUList& localSizes,
+    const bool checkOverflow
+)
+{
+    labelList values;
+
+    const label len = localSizes.size();
+
+    if (len)
+    {
+        values.resize(len+1);
+
+        label start = 0;
+        for (label i = 0; i < len; ++i)
+        {
+            values[i] = start;
+            start += localSizes[i];
+
+            if (checkOverflow && start < values[i])
+            {
+                FatalErrorInFunction
+                    << "Overflow : sum of sizes exceeds labelMax ("
+                    << labelMax << ") after index " << i << " of "
+                    << flatOutput(localSizes) << nl
+                    << "Please recompile with larger datatype for label." << nl
+                    << exit(FatalError);
+            }
+        }
+        values[len] = start;
+    }
+
+    return values;
+}
+
+
+Foam::List<Foam::labelRange>
+Foam::globalIndex::calcRanges
+(
+    const labelUList& localSizes,
+    const bool checkOverflow
+)
+{
+    List<labelRange> values;
+
+    const label len = localSizes.size();
+
+    if (len)
+    {
+        values.resize(len);
+
+        label start = 0;
+        for (label i = 0; i < len; ++i)
+        {
+            values[i].reset(start, localSizes[i]);
+            start += localSizes[i];
+
+            if (checkOverflow && start < values[i].start())
+            {
+                FatalErrorInFunction
+                    << "Overflow : sum of sizes exceeds labelMax ("
+                    << labelMax << ") after index " << i << " of "
+                    << flatOutput(localSizes) << nl
+                    << "Please recompile with larger datatype for label." << nl
+                    << exit(FatalError);
+            }
+        }
+    }
+
+    return values;
+}
+
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
@@ -52,8 +130,8 @@ void Foam::globalIndex::bin
     bins.m() = UIndirectList<label>(globalIds, order);
 
     labelList& binOffsets = bins.offsets();
-    binOffsets.setSize(offsets.size());
-    binOffsets = 0;
+    binOffsets.resize_nocopy(offsets.size());
+    binOffsets = Zero;
 
     validBins.clear();
 
@@ -106,33 +184,80 @@ void Foam::globalIndex::reset
     const bool parallel
 )
 {
-    offsets_.resize(Pstream::nProcs(comm)+1);
+    const label len = Pstream::nProcs(comm);
 
-    labelList localSizes(Pstream::nProcs(comm), Zero);
-    localSizes[Pstream::myProcNo(comm)] = localSize;
-
-    if (parallel)
+    if (len)
     {
-        Pstream::gatherList(localSizes, tag, comm);
-        Pstream::scatterList(localSizes, tag, comm);
-    }
+        // Seed with localSize, zero elsewhere (for non-parallel branch)
+        labelList localSizes(len, Zero);
+        localSizes[Pstream::myProcNo(comm)] = localSize;
 
-    label offset = 0;
-    offsets_[0] = 0;
-    for (const int proci : Pstream::allProcs(comm))
-    {
-        const label oldOffset = offset;
-        offset += localSizes[proci];
-
-        if (offset < oldOffset)
+        if (parallel)
         {
-            FatalErrorInFunction
-                << "Overflow : sum of sizes " << localSizes
-                << " exceeds capability of label (" << labelMax
-                << "). Please recompile with larger datatype for label."
-                << exit(FatalError);
+            Pstream::gatherList(localSizes, tag, comm);
+            Pstream::scatterList(localSizes, tag, comm);
+        }
+
+        reset(localSizes, true);  // checkOverflow = true
+    }
+    else
+    {
+        offsets_.clear();
+    }
+}
+
+
+void Foam::globalIndex::reset
+(
+    const labelUList& localSizes,
+    const bool checkOverflow
+)
+{
+    const label len = localSizes.size();
+
+    if (len)
+    {
+        offsets_.resize_nocopy(len+1);
+
+        label start = 0;
+        for (label i = 0; i < len; ++i)
+        {
+            offsets_[i] = start;
+            start += localSizes[i];
+
+            if (checkOverflow && start < offsets_[i])
+            {
+                FatalErrorInFunction
+                    << "Overflow : sum of sizes exceeds labelMax ("
+                    << labelMax << ") after index " << i << " of "
+                    << flatOutput(localSizes) << nl
+                    << "Please recompile with larger datatype for label." << nl
+                    << exit(FatalError);
+            }
+        }
+        offsets_[len] = start;
+    }
+    else
+    {
+        offsets_.clear();
+    }
+}
+
+
+void Foam::globalIndex::setLocalSize(const label proci, const label len)
+{
+    if (proci >= 0 && proci+1 < offsets_.size() && len >= 0)
+    {
+        const label delta = (len - (offsets_[proci+1] - offsets_[proci]));
+
+        // TBD: additional overflow check
+        if (delta)
+        {
+            for (label i = proci+1; i < offsets_.size(); ++i)
+            {
+                offsets_[i] += delta;
+            }
         }
-        offsets_[proci+1] = offset;
     }
 }
 
@@ -159,6 +284,33 @@ Foam::labelList Foam::globalIndex::sizes() const
 }
 
 
+Foam::List<Foam::labelRange>
+Foam::globalIndex::ranges() const
+{
+    List<labelRange> values;
+
+    const label len = (offsets_.size() - 1);
+
+    if (len < 1)
+    {
+        return values;
+    }
+
+    values.resize(len);
+
+    for (label proci=0; proci < len; ++proci)
+    {
+        values[proci].reset
+        (
+            offsets_[proci],
+            (offsets_[proci+1] - offsets_[proci])
+        );
+    }
+
+    return values;
+}
+
+
 Foam::label Foam::globalIndex::maxNonLocalSize(const label proci) const
 {
     const label len = (offsets_.size() - 1);

src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndex.H

@@ -68,6 +68,12 @@ Ostream& operator<<(Ostream& os, const globalIndex& gi);
 
 class globalIndex
 {
+    // Private Data
+
+        //- Start of proci. Size is nProcs()+1. (so like CompactListList)
+        labelList offsets_;
+
+
     // Private Member Functions
 
         //- Sort and bin. validBins contains bins with non-zero size.
@@ -80,26 +86,42 @@ class globalIndex
             DynamicList<label>& validBins
         );
 
-
-    // Private Data
-
-        //- Start of proci. Size is nProcs()+1. (so like CompactListList)
-        labelList offsets_;
-
-
 public:
 
+    // Public Data Types
+
+        //- Disambiguation tag (list construction dispatch)
+        enum accessType : char { OFFSETS, SIZES };
+
+
     // Constructors
 
         //- Default construct
         globalIndex() = default;
 
-        //- Construct from local max size.
-        //  Does communication with default communicator and message tag.
+        //- Copy construct from a list of offsets.
+        //- No communication required
+        inline explicit globalIndex(const labelUList& listOffsets);
+
+        //- Move construct from a list of offsets.
+        //- No communication required
+        inline explicit globalIndex(labelList&& listOffsets);
+
+        //- Copy construct from a list of offsets or sizes.
+        //- No communication required
+        inline globalIndex
+        (
+            const labelUList& offsetsOrSizes,
+            enum accessType accType
+        );
+
+        //- Construct from local size.
+        //  Communication with default communicator and message tag.
         inline explicit globalIndex(const label localSize);
 
-        //- Construct from local max size.
-        //  Does communication with given communicator and message tag
+        //- Construct from local size.
+        //  Communication with given communicator and message tag,
+        //  unless parallel == false
         inline globalIndex
         (
             const label localSize,
@@ -108,13 +130,8 @@ public:
             const bool parallel     //!< use parallel comms
         );
 
-        //- Copy construct from list of labels
-        inline explicit globalIndex(const labelUList& offsets);
-
-        //- Move construct from list of labels
-        inline explicit globalIndex(labelList&& offsets);
-
-        //- Construct from Istream
+        //- Construct from Istream.
+        //- No communication required
         explicit globalIndex(Istream& is);
 
 
@@ -123,9 +140,6 @@ public:
         //- Check for default constructed or global sum == 0
         inline bool empty() const;
 
-        //- The number of processors covered by the offsets
-        inline label nProcs() const noexcept;
-
         //- Global sum of localSizes
         inline label size() const;
 
@@ -142,6 +156,18 @@ public:
         inline const labelList& offsets() const noexcept;
 
 
+    // Dimensions
+
+        //- The number of processors covered by the offsets
+        inline label nProcs() const noexcept;
+
+        //- Range of process indices for all addressed offsets (processes)
+        inline labelRange allProcs() const noexcept;
+
+        //- Range of process indices for addressed sub-offsets (processes)
+        inline labelRange subProcs() const noexcept;
+
+
     // Edit
 
         //- Write-access to the offsets, for changing after construction
@@ -152,7 +178,8 @@ public:
         inline void reset(const label localSize);
 
         //- Reset from local size.
-        //  Does communication with given communicator and message tag
+        //  Does communication with given communicator and message tag,
+        //  unless parallel == false
         void reset
         (
             const label localSize,
@@ -161,8 +188,20 @@ public:
             const bool parallel     //!< use parallel comms
         );
 
+        //- Reset from list of local sizes,
+        //- with optional check for label overflow.
+        //- No communication required
+        void reset
+        (
+            const labelUList& sizes,
+            const bool checkOverflow = false
+        );
 
-        // Queries
+        //- Alter local size for given processor
+        void setLocalSize(const label proci, const label len);
+
+
+    // Queries
 
         // Queries relating to my processor (using world communicator)
 
@@ -178,6 +217,9 @@ public:
             //- Return start/size range of local processor data
             inline labelRange range() const;
 
+            //- Return start/size ranges for all data
+            List<labelRange> ranges() const;
+
             //- Is on local processor
             inline bool isLocal(const label i) const;
 
@@ -240,6 +282,99 @@ public:
             inline label whichProcID(const label i) const;
 
 
+    // Iteration
+
+        //- Forward input iterator with const access
+        class const_iterator
+        {
+            //- The parent class for which this is an iterator
+            const globalIndex* parent_;
+
+            //- The index into the parent
+            label proci_;
+
+
+        public:
+
+        // Constructors
+
+            //- Construct from globalIndex list at given index
+            explicit const_iterator
+            (
+                const globalIndex* globalIdx,
+                const label proci = 0
+            ) noexcept;
+
+
+        // Member Operators
+
+            //- The associated local proc
+            inline label proci() const noexcept;
+
+            //- The local start
+            inline label start() const;
+
+            //- The local size
+            inline label size() const;
+
+            //- The local range
+            inline labelRange range() const;
+
+            //- The local range
+            inline labelRange operator*() const;
+
+            inline const_iterator& operator++();
+            inline const_iterator operator++(int);
+
+            inline const_iterator& operator--();
+            inline const_iterator operator--(int);
+
+            inline bool operator==(const const_iterator& iter) const noexcept;
+            inline bool operator!=(const const_iterator& iter) const noexcept;
+        };
+
+
+        //- A const_iterator set to the beginning
+        inline const_iterator cbegin() const noexcept;
+
+        //- A const_iterator set to beyond the end
+        inline const const_iterator cend() const noexcept;
+
+        //- A const_iterator set to the beginning
+        inline const_iterator begin() const noexcept;
+
+        //- A const_iterator set to beyond the end
+        inline const const_iterator end() const noexcept;
+
+
+    // Helper Functions
+
+        //- Calculate offsets from a list of local sizes,
+        //- with optional check for label overflow
+        static labelList calcOffsets
+        (
+            const labelUList& localSizes,
+            const bool checkOverflow = false
+        );
+
+        //- Calculate offsets from list of lists,
+        //- with optional check for label overflow
+        template<class SubListType>
+        static labelList calcListOffsets
+        (
+            const List<SubListType>& lists,
+            const bool checkOverflow = false
+        );
+
+        //- Calculate ranges (offset/size) from a list of local sizes,
+        //- with optional check for label overflow
+        static List<labelRange> calcRanges
+        (
+            const labelUList& localSizes,
+            const bool checkOverflow = false
+        );
+
+
         // Other
 
             //- Collect data in processor order on master (== procIDs[0]).

src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexI.H

@@ -31,9 +31,53 @@ License
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
+inline Foam::globalIndex::globalIndex
+(
+    const labelUList& listOffsets
+)
+{
+    if (listOffsets.size() > 1)
+    {
+        offsets_ = listOffsets;
+    }
+}
+
+
+inline Foam::globalIndex::globalIndex
+(
+    labelList&& listOffsets
+)
+{
+    if (listOffsets.size() > 1)
+    {
+        offsets_.transfer(listOffsets);
+    }
+    else
+    {
+        listOffsets.clear();
+    }
+}
+
+
+inline Foam::globalIndex::globalIndex
+(
+    const labelUList& offsetsOrSizes,
+    enum globalIndex::accessType accType
+)
+{
+    if (accType == accessType::SIZES)
+    {
+        reset(offsetsOrSizes);
+    }
+    else if (offsetsOrSizes.size() > 1)
+    {
+        // accessType::OFFSETS
+        offsets_ = offsetsOrSizes;
+    }
+}
+
+
 inline Foam::globalIndex::globalIndex(const label localSize)
-:
-    globalIndex()
 {
     reset(localSize);
 }
@@ -46,25 +90,11 @@ inline Foam::globalIndex::globalIndex
     const label comm,
     const bool parallel
 )
-:
-    globalIndex()
 {
     reset(localSize, tag, comm, parallel);
 }
 
 
-inline Foam::globalIndex::globalIndex(const labelUList& offsets)
-:
-    offsets_(offsets)
-{}
-
-
-inline Foam::globalIndex::globalIndex(labelList&& offsets)
-:
-    offsets_(std::move(offsets))
-{}
-
-
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
 inline bool Foam::globalIndex::empty() const
@@ -76,7 +106,23 @@ inline bool Foam::globalIndex::empty() const
 inline Foam::label Foam::globalIndex::nProcs() const noexcept
 {
     const label len = (offsets_.size() - 1);
-    return (len < 1) ? 0 : len;
+    return (len < 1) ? static_cast<label>(0) : len;
+}
+
+
+inline Foam::labelRange Foam::globalIndex::allProcs() const noexcept
+{
+    // Proc 0 -> nProcs
+    const label len = (offsets_.size() - 1);
+    return (len < 1) ? labelRange() : labelRange(0, len);
+}
+
+
+inline Foam::labelRange Foam::globalIndex::subProcs() const noexcept
+{
+    // Proc 1 -> nProcs
+    const label len = (offsets_.size() - 2);
+    return (len < 1) ? labelRange() : labelRange(1, len);
 }
 
 
@@ -104,7 +150,7 @@ inline const Foam::labelUList Foam::globalIndex::localStarts() const
 
 inline Foam::label Foam::globalIndex::size() const
 {
-    return offsets_.empty() ? 0 : offsets_.last();
+    return offsets_.empty() ? static_cast<label>(0) : offsets_.last();
 }
 
 
@@ -276,4 +322,143 @@ inline Foam::label Foam::globalIndex::whichProcID(const label i) const
 }
 
 
+// * * * * * * * * * * * * * * * * Iterators * * * * * * * * * * * * * * * * //
+
+inline Foam::globalIndex::const_iterator::
+const_iterator
+(
+    const globalIndex* globalIdx,
+    const label i
+) noexcept
+:
+    parent_(globalIdx),
+    proci_(i)
+{}
+
+
+inline Foam::label Foam::globalIndex::const_iterator::
+proci() const noexcept
+{
+    return proci_;
+}
+
+
+inline Foam::label Foam::globalIndex::const_iterator::
+start() const
+{
+    return (*parent_).localStart(proci_);
+}
+
+
+inline Foam::label Foam::globalIndex::const_iterator::
+size() const
+{
+    return (*parent_).localSize(proci_);
+}
+
+
+inline Foam::labelRange Foam::globalIndex::const_iterator::
+range() const
+{
+    return (*parent_).range(proci_);
+}
+
+
+inline Foam::labelRange Foam::globalIndex::const_iterator::
+operator*() const
+{
+    return this->range();
+}
+
+
+inline Foam::globalIndex::const_iterator&
+Foam::globalIndex::const_iterator::
+operator++()
+{
+    ++proci_;
+    return *this;
+}
+
+
+inline Foam::globalIndex::const_iterator
+Foam::globalIndex::const_iterator::
+operator++(int)
+{
+    const_iterator old(*this);
+    ++proci_;
+    return old;
+}
+
+
+inline Foam::globalIndex::const_iterator&
+Foam::globalIndex::const_iterator::
+operator--()
+{
+    --proci_;
+    return *this;
+}
+
+
+inline Foam::globalIndex::const_iterator
+Foam::globalIndex::const_iterator::
+operator--(int)
+{
+    const_iterator old(*this);
+    --proci_;
+    return old;
+}
+
+
+inline bool
+Foam::globalIndex::const_iterator::
+operator==
+(
+    const const_iterator& iter
+) const noexcept
+{
+    return (proci_ == iter.proci_);
+}
+
+
+inline bool
+Foam::globalIndex::const_iterator::
+operator!=
+(
+    const const_iterator& iter
+) const noexcept
+{
+    return (proci_ != iter.proci_);
+}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+inline Foam::globalIndex::const_iterator
+Foam::globalIndex::cbegin() const noexcept
+{
+    return const_iterator(this);
+}
+
+
+inline const Foam::globalIndex::const_iterator
+Foam::globalIndex::cend() const noexcept
+{
+    return const_iterator(this, this->nProcs());
+}
+
+
+inline Foam::globalIndex::const_iterator
+Foam::globalIndex::begin() const noexcept
+{
+    return const_iterator(this);
+}
+
+
+inline const Foam::globalIndex::const_iterator
+Foam::globalIndex::end() const noexcept
+{
+    return const_iterator(this, this->nProcs());
+}
+
+
 // ************************************************************************* //

src/OpenFOAM/meshes/polyMesh/globalMeshData/globalIndexTemplates.C

@@ -28,6 +28,46 @@ License
 
 #include "globalIndex.H"
 
+// * * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * //
+
+template<class SubListType>
+Foam::labelList
+Foam::globalIndex::calcListOffsets
+(
+    const List<SubListType>& lists,
+    const bool checkOverflow
+)
+{
+    labelList values;
+
+    const label len = lists.size();
+
+    if (len)
+    {
+        values.resize(len+1);
+
+        label start = 0;
+        for (label i = 0; i < len; ++i)
+        {
+            values[i] = start;
+            start += lists[i].size();
+
+            if (checkOverflow && start < values[i])
+            {
+                FatalErrorInFunction
+                    << "Overflow : sum of sizes exceeds labelMax ("
+                    << labelMax << ") after index " << i << nl
+                    << "Please recompile with larger datatype for label." << nl
+                    << exit(FatalError);
+            }
+        }
+        values[len] = start;
+    }
+
+    return values;
+}
+
+
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
 template<class Container, class Type>