Make MFParallelFor safer from int overflow

Src/Base/AMReX_BaseFabUtility.H

@@ -53,14 +53,14 @@ void fill (BaseFab<STRUCT>& aos_fab, F && f)
             std::uint64_t const threadIdxx = handler.threadIdx();
             std::uint64_t const blockIdxx = handler.blockIdx();
             auto const shared = (T*)handler.sharedMemory();
-            if (icell < ntotcells) {
+            if (icell < indexer.numPts()) {
                 auto ga = new(shared+threadIdxx*STRUCTSIZE) STRUCT;
                 auto [i, j, k] = indexer(icell);
                 f(*ga, i, j, k);
             }
             handler.sharedBarrier();
             for (std::uint64_t m = threadIdxx,
-                     mend = amrex::min<std::uint64_t>(blockDimx, ntotcells-blockDimx*blockIdxx) * STRUCTSIZE;
+                     mend = amrex::min<std::uint64_t>(blockDimx, indexer.numPts()-blockDimx*blockIdxx) * STRUCTSIZE;
                  m < mend; m += blockDimx) {
                 p[blockDimx*blockIdxx*STRUCTSIZE+m] = shared[m];
             }
@@ -72,14 +72,14 @@ void fill (BaseFab<STRUCT>& aos_fab, F && f)
             std::uint64_t const icell = std::uint64_t(blockDim.x)*blockIdx.x+threadIdx.x;
             Gpu::SharedMemory<T> gsm;
             T* const shared = gsm.dataPtr();
-            if (icell < ntotcells) {
+            if (icell < indexer.numPts()) {
                 auto ga = new(shared+std::uint64_t(threadIdx.x)*STRUCTSIZE) STRUCT;
                 auto [i, j, k] = indexer(icell);
                 f(*ga, i, j, k);
             }
             __syncthreads();
             for (std::uint64_t m = threadIdx.x,
-                     mend = amrex::min<std::uint64_t>(blockDim.x, ntotcells-std::uint64_t(blockDim.x)*blockIdx.x) * STRUCTSIZE;
+                     mend = amrex::min<std::uint64_t>(blockDim.x, indexer.numPts()-std::uint64_t(blockDim.x)*blockIdx.x) * STRUCTSIZE;
                  m < mend; m += blockDim.x) {
                 p[std::uint64_t(blockDim.x)*blockIdx.x*STRUCTSIZE+m] = shared[m];
             }

Src/Base/AMReX_Box.H

@@ -1842,13 +1842,16 @@ Box makeSingleCellBox (int i, int j, int k, IndexType typ = IndexType::TheCellTy
 
 struct BoxIndexer
 {
+    std::uint64_t npts;
+
 #if (AMREX_SPACEDIM == 3)
     Math::FastDivmodU64 fdxy;
     Math::FastDivmodU64 fdx;
     IntVect lo;
 
     BoxIndexer (Box const& box)
-        : fdxy(std::uint64_t(box.length(0))*std::uint64_t(box.length(1))),
+        : npts(box.numPts()),
+          fdxy(std::uint64_t(box.length(0))*std::uint64_t(box.length(1))),
           fdx (std::uint64_t(box.length(0))),
           lo  (box.smallEnd())
         {}
@@ -1877,7 +1880,8 @@ struct BoxIndexer
     IntVect lo;
 
     BoxIndexer (Box const& box)
-        : fdx (std::uint64_t(box.length(0))),
+        : npts(box.numPts()),
+          fdx (std::uint64_t(box.length(0))),
           lo  (box.smallEnd())
         {}
 
@@ -1902,7 +1906,8 @@ struct BoxIndexer
     int lo;
 
     BoxIndexer (Box const& box)
-        : lo(box.smallEnd(0))
+        : npts(box.numPts()),
+          lo(box.smallEnd(0))
         {}
 
     [[nodiscard]] AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
@@ -1918,6 +1923,9 @@ struct BoxIndexer
     }
 
 #endif
+
+    [[nodiscard]] AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
+    std::uint64_t numPts () const { return npts; }
 };
 
 }

Src/Base/AMReX_FabArrayBase.H

@@ -651,7 +651,7 @@ public:
         ~ParForInfo ();
 
         std::pair<int*,int*> const& getBlocks () const { return m_nblocks_x; }
-        Box const* getBoxes () const { return m_boxes; }
+        BoxIndexer const* getBoxes () const { return m_boxes; }
 
         ParForInfo () = delete;
         ParForInfo (ParForInfo const&) = delete;
@@ -663,7 +663,7 @@ public:
         IntVect m_ng;
         int m_nthreads;
         std::pair<int*,int*> m_nblocks_x;
-        Box* m_boxes = nullptr;
+        BoxIndexer* m_boxes = nullptr;
         char* m_hp = nullptr;
         char* m_dp = nullptr;
     };