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// Tideland Go Library - Sort
//
// Copyright (C) 2009-2017 Frank Mueller / Tideland / Oldenburg / Germany
//
// All rights reserved. Use of this source code is governed
// by the new BSD license.
package sort
//--------------------
// IMPORTS
//--------------------
import (
"runtime"
"sort"
)
//--------------------
// CONTROL VALUES
//--------------------
// sequentialThreshold for switching from sequential quick sort to insertion sort.
var sequentialThreshold int = runtime.NumCPU()*4 - 1
// parallelThreshold for switching from parallel to sequential quick sort.
var parallelThreshold int = runtime.NumCPU()*2048 - 1
//--------------------
// HELPING FUNCS
//--------------------
// insertionSort for smaller data collections.
func insertionSort(data sort.Interface, lo, hi int) {
for i := lo + 1; i < hi+1; i++ {
for j := i; j > lo && data.Less(j, j-1); j-- {
data.Swap(j, j-1)
}
}
}
// median to caclculate the median based on Tukey's ninther.
func median(data sort.Interface, lo, hi int) int {
m := (lo + hi) / 2
d := (hi - lo) / 8
// Move median into the middle.
mot := func(ml, mm, mh int) {
if data.Less(mm, ml) {
data.Swap(mm, ml)
}
if data.Less(mh, mm) {
data.Swap(mh, mm)
}
if data.Less(mm, ml) {
data.Swap(mm, ml)
}
}
// Get low, middle, and high median.
if hi-lo > 40 {
mot(lo+d, lo, lo+2*d)
mot(m-d, m, m+d)
mot(hi-d, hi, hi-2*d)
}
// Get combined median.
mot(lo, m, hi)
return m
}
// partition the data based on the median.
func partition(data sort.Interface, lo, hi int) (int, int) {
med := median(data, lo, hi)
idx := lo
data.Swap(med, hi)
for i := lo; i < hi; i++ {
if data.Less(i, hi) {
data.Swap(i, idx)
idx++
}
}
data.Swap(idx, hi)
return idx - 1, idx + 1
}
// sequentialQuickSort using itself recursively.
func sequentialQuickSort(data sort.Interface, lo, hi int) {
if hi-lo > sequentialThreshold {
// Use sequential quicksort.
plo, phi := partition(data, lo, hi)
sequentialQuickSort(data, lo, plo)
sequentialQuickSort(data, phi, hi)
} else {
// Use insertion sort.
insertionSort(data, lo, hi)
}
}
// parallelQuickSort using itself recursively and concurrent.
func parallelQuickSort(data sort.Interface, lo, hi int, done chan bool) {
if hi-lo > parallelThreshold {
// Parallel QuickSort.
plo, phi := partition(data, lo, hi)
partDone := make(chan bool)
go parallelQuickSort(data, lo, plo, partDone)
go parallelQuickSort(data, phi, hi, partDone)
// Wait for the end of both sorts.
<-partDone
<-partDone
} else {
// Sequential QuickSort.
sequentialQuickSort(data, lo, hi)
}
// Signal that it's done.
done <- true
}
//--------------------
// PARALLEL QUICKSORT
//--------------------
// Sort is the single function for sorting data according
// to the standard sort interface. Internally it uses the
// parallel quicksort.
func Sort(data sort.Interface) {
done := make(chan bool)
go parallelQuickSort(data, 0, data.Len()-1, done)
<-done
}
// EOF
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