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merge sort parallelly, reuse slice
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| package main | |
| import ( | |
| "sync" | |
| ) | |
| const parallelBySliceLength = 1 << 10 * 3 | |
| func MergeSortLoop(src []int64) { | |
| srcReadOnly := make([]int64, len(src))//update only in merge stage | |
| copy(srcReadOnly, src) | |
| mergeSortDivideLoop(src, srcReadOnly, 0, len(src)) | |
| } | |
| func mergeSortDivideLoop(srcWriteOnly, srcReadOnly []int64, indexLeftPart, indexRightPart int) { | |
| srcLen := indexRightPart - indexLeftPart | |
| if indexRightPart <= indexLeftPart || srcLen == 1 { | |
| return | |
| } | |
| mid := (indexRightPart + indexLeftPart) / 2 | |
| const parallelBySliceLength = 1 << 10 | |
| if mid-indexLeftPart > parallelBySliceLength || indexRightPart-mid > parallelBySliceLength { | |
| var wg sync.WaitGroup | |
| wg.Add(2) | |
| go func() { | |
| defer wg.Done() | |
| mergeSortDivideLoop(srcWriteOnly, srcReadOnly, indexLeftPart, mid) | |
| return | |
| }() | |
| go func() { | |
| defer wg.Done() | |
| mergeSortDivideLoop(srcWriteOnly, srcReadOnly, mid, indexRightPart) | |
| return | |
| }() | |
| wg.Wait() | |
| mergeSortConqueLoop(srcWriteOnly, srcReadOnly, indexLeftPart, indexRightPart) | |
| return | |
| } | |
| mergeSortDivideLoop(srcWriteOnly, srcReadOnly, indexLeftPart, mid) | |
| mergeSortDivideLoop(srcWriteOnly, srcReadOnly, mid, indexRightPart) | |
| mergeSortConqueLoop(srcWriteOnly, srcReadOnly, indexLeftPart, indexRightPart) | |
| return | |
| } | |
| func mergeSortConqueLoop(srcWriteOnly, srcReadOnly []int64, indexLeftPart, indexRightPart int) { | |
| mid := (indexRightPart + indexLeftPart) / 2 | |
| indexLeftPartMove, indexRightPartMove, IndexRetMove := indexLeftPart, mid, indexLeftPart | |
| for { | |
| if indexLeftPartMove < mid && indexRightPartMove < indexRightPart { | |
| if srcReadOnly[indexLeftPartMove] <= srcReadOnly[indexRightPartMove] { | |
| srcWriteOnly[IndexRetMove] = srcReadOnly[indexLeftPartMove] | |
| indexLeftPartMove++ | |
| } else { | |
| srcWriteOnly[IndexRetMove] = srcReadOnly[indexRightPartMove] | |
| indexRightPartMove++ | |
| } | |
| IndexRetMove++ | |
| } else { | |
| break | |
| } | |
| } | |
| for i := indexLeftPartMove; i < mid; i++ { | |
| srcWriteOnly[IndexRetMove] = srcReadOnly[i] | |
| IndexRetMove++ | |
| } | |
| for i := indexRightPartMove; i < indexRightPart; i++ { | |
| srcWriteOnly[IndexRetMove] = srcReadOnly[i] | |
| IndexRetMove++ | |
| } | |
| for i := indexLeftPart; i < indexRightPart; i++ { | |
| srcReadOnly[i] = srcWriteOnly[i] | |
| } | |
| return | |
| } |
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original, no reuse no parallel processing
reuse src only
parallel processing, no reuse merge slice
parallel processing, reuse merge slice by global slice