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Note: this last value is required forthe current version of the compiler, but it will be droped in future releases.Is_Local(int index) checks whether a pC++ collection element of an index \index"is stored in local processor's memory. It returns \true" if the element is in the local memory and \false" otherwise. Is_Local(int index1, int index2) is the two-dimensionalimplementation with \index1" being the rst index and \index2" the second.Get_Element(int index) returns a pointer to a collection element with the index, \index." If the element is local it returns a pointer to the element. If the element is not local, ona distributed-memory machine, it fetches the element and stores it in a local buer and thenreturns a pointer to the buer, or simply returns a pointer to the element on a shared-memorymachine regardless of the element is local or not. Get_Element(int index1, int index2)is the two-dimensional implementation.60returns a pointer to a segmentof an element.
Like, it fetches the segment of the element if necessary. \index"again is the index of the element. \oset" is the oset of a eld of the element with respectto the beginning of the element. \oset" has to be given in terms of integers. \size" is thesize of the eld in terms of integers. As an example, if myElement is declared asGet_ElementPart(int index, int offset, int size)Get_Elementclass myElement {public:int i, j;double a[10];void foo();}the oset of the eld a and the size are then given byoffset = ((char*)&myElement.a[0] - (char*)&myElement) / sizeof(int);size = 10*sizeof(double)/sizeof(int).,, andreturn an integer, a oating point, or a double oating point eld, respectively.
\index" is the index of the elementand \oset" is the oset of the eld in integers.Similar to Get Element(int index), Get CopyElem(int index) fetches a copy of anelement. However, instead of using the only buer to store the fetched copy, it creates a newbuer for the fetched copy. This copy can be deleted or overwritten only by the user.Get ElementPart Int(int index,int offset) Get ElementPart Float(int index,intoffset)Get ElementPart Double(int index,int offset)8.1 The pC++ SuperKernel collectionThe SuperKernel collection inherits Kernel class, therefore, all functionalities available to theKernel class are available as \methods of collection" in Superkernel. SuperKernel is designedas a base collection so that new collections can be derived from it.
It provides a few basicelement access functions. The declaration of the SuperKernel is as follows:Collection SuperKernel : public Kernel {public:int dim1size;int dim2size;SuperKernel(Distribution *T, Align *A);ElementType *operator()(int i);ElementType *operator()(int i, int j);MethodOfElement:int Ident;int index1;int index2;61SuperKernel<ElementType> *ThisCollection;ElementType *Self(int i);ElementType *Self(int i, int j);};In the \methods of collection" part (part before the MethodOfElement statement), \dim1size"and \dim2size" denote the rst and second dimension sizes of the collection.
They are setby the alignment parameter, Align, in the collection constructor. Operators (int i) and(int i, int j) are overloaded. So instead of using Get_Element(), a user uses these operators to fetch elements. Suppose we construct a one-dimensional collection of myElementby calling SuperKernel constructor,SuperKernel<myElement> S(&D, &A);S(10) then returns a pointer to the 11th element of the collection and S(10)->a will return apointer to the array \a." Meanwhile, S(10)->a[5] will return the 6th element in the array.In the \methods of elements" part (part after the MethodOfElement statement), \index1"and \index2" denote the indexes assigned to a collection element.
These indexes can beaccessed by an element. For example, in a two-dimensional collection, function foo() can bedened asvoid myElement::foo() {if(index1 == 1) printf("Hello from element (%d, %d)\n", index1, index2);}In this example, all elements with index1 = 1 print the message.The pointer \ThisCollection" provides a way for the methods of element to access methods of collection. Without it methods of element cannot execute a method of collection.
Wecan modify the above example to allow foo() access a collection element:void myElement::foo() {a[5] = (*ThisCollection)(2,3)->a[5];}In this example the value of a[5] of collection element (2,3) is assigned to a[5] of the currentelement. Since every element executes this operation, the value of a[5] of element (2,3)is broadcast to other elements in the collection.
Note that currently this is not an ecientway to broadcast, because (*ThisCollection)(2,3) simply invokes the overloaded operatorwhich fetches the entire element (2,3) and returns a pointer to the copy. In our future release,the compiler will convert this to Get ElementPartDouble so that only array element a[5] isfetched.The \Self" functions in methods of element provide another convenient way for an elementto address other elements in a collection. The integers \i" and \j" represent index osetsto the current element. As an example, Self(1,1) would return the element with indexes(index1+1, index2+1), where index1 and index2 are the indexes of the current element.629 The DistributedArray CollectionDistributedArray provides the a number of functions for the user-interface. The denitionof the collection and some useful functions are given below. Functions and variables internalto the collection are omitted.Collection DistributedArray : public SuperKernel {public:DistributedArray(Distribution *T, Align *A);void Assign(int i, ElementType &e);void Assign(int i, int j, ElementType &e);DistributedArray<ElementType>&operator = (DistributedArray<ElementType> &rhs);void Shift(int dim, int distance);void Reduce();void ReduceDim1();void ReduceDim2();void Broadcast();void BroadcastDim1();void BroadcastDim2();double DotProd(DistributedArray<ElementType> &arg1);MethodOfElement:void WhereAmI();virtual double Dot(ElementType &arg1);virtual ElementType &operator +=(ElementType &rhs);double dotprodtemp;};is the constructor of the collection.It has class objects Distribution and Align as its arguments.Assign(int i, ElementType &e) copies an element of DistributedArray element type,argument \e," to an element of an index \i" of the invokingDistributedArray(Distribution *T, Align *A)DistributedArray object.Assign(int i, int j, ElementType &e)is its two-dimensional counter part.Operator \=" is overloaded.
It copies a DistributedArray object to another DistributedArray object.Shift(int dim, int distance) performs a circular shift of collection elements parallelto a given dimension of the collection by a given distance. Elements shifted out at one endare shifted in at the other end.
For example, Shift(1, 2) will shift elements parallel to therst dimension by a distance of 2.Reduce() applies a global reduction to collection elements. Elements are summed together, the result is stored in element \0," the very rst element in the collection.
It is63assumed that the total number of elements in the collection is a power of two. A user needsto dene function &operator +=(ElementType &rhs) before invoking this function.ReduceDim1() applies a reduction parallel to the rst dimension of the collection. Elements are summed together along columns, if the rst index is dened as the row indexand the second as the column index. The results are stored in elements in the rst row.It is assumed that the number of rows is a power of two. A user needs to dene function&operator +=(ElementType &rhs) before invoking this function.ReduceDim2() applies a reduction parallel to the second dimension of the collection.Elements are summed together along rows. The results are stored in elements in the rstcolumn.
It is assumed that the number of columns is a power of two. A user needs to denefunction &operator +=(ElementType &rhs) before invoking this function.Broadcast() broadcasts element zero to all others elements in a collection. After thebroadcast, each element gets an exact copy of the rst element in the collection.
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