cumulate (original) (raw)

Brian Goetz brian.goetz at oracle.com
Wed Dec 26 14:56:13 PST 2012

Grabbed and committed.

On 12/22/2012 1:55 PM, Doug Lea wrote:

On 12/21/12 16:31, Brian Goetz wrote:

It's gone. (Well, not gone. Mercurial history is still there.)

I propose this as the replacement: In Arrays: void parallelPrefix(T[], int offset, int length, BinaryOperator); void parallelPrefix(int[], int offset, int length, IntBinaryOperator); void parallelPrefix(long[], int offset, int length, LongBinaryOperator); void parallelPrefix(double[], int offset, int length, DoubleBinaryOperator); Actually, to be consistent with Arrays.sort (and other in-place methods in Arrays), it should use fromIndex, toIndex. The "T" and long versions pasted below. After Brian grabs and commits some stuff, it should all be in place.... -Doug /** * Cumulates in parallel each element of the given array in place, * using the supplied function. For example if the array initially * holds {@code [2, 1, 0, 3]} and the operation performs addition, * then upon return the array holds {@code [2, 3, 3, 6]}. * Parallel prefix computation is usually more efficient than * sequential loops for large arrays. * * @param array the array, which is modified in-place by this method * @param op the function to perform cumulations. The function * must be amenable to left-to-right application through the * elements of the array, as well as possible left-to-right * application across segments of the array. */ public static void parallelPrefix(T[] array, BinaryOperator op) { if (array.length > 0) new ArrayPrefixUtil.CumulateTask (null, op, array, 0, array.length).invoke(); } /** * Performs {@link #parallelPrefix(Object[], BinaryOperator)} * for the given subrange of the array. * * @param array the array * @param fromIndex the index of the first element, inclusive * @param toIndex the index of the last element, exclusive * @param op the function to perform cumulations. * @throws IllegalArgumentException if {@code fromIndex > toIndex} * @throws ArrayIndexOutOfBoundsException * if {@code fromIndex < 0} or {@code toIndex > array.length} */ public static void parallelPrefix(T[] array, int fromIndex, int toIndex, BinaryOperator op) { checkFromToBounds(array.length, fromIndex, toIndex); if (fromIndex < toIndex)_ _new ArrayPrefixUtil.CumulateTask_ _(null, op, array, fromIndex, toIndex).invoke();_ _}_ _/**_ _* Cumulates in parallel each element of the given array in place,_ _* using the supplied function. For example if the array initially_ _* holds {@code [2, 1, 0, 3]} and the operation performs addition,_ _* then upon return the array holds {@code [2, 3, 3, 6]}._ _* Parallel prefix computation is usually more efficient than_ _* sequential loops for large arrays._ _*_ _* @param array the array, which is modified in-place by this method_ _* @param op the function to perform cumulations. The function_ _* must be amenable to left-to-right application through the_ _* elements of the array, as well as possible left-to-right_ _* application across segments of the array._ _*/_ _public static void parallelPrefix(long[] array, LongBinaryOperator_ _op) {_ _if (array.length > 0) new ArrayPrefixUtil.LongCumulateTask (null, op, array, 0, array.length).invoke(); } ... and others similarly...

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