gistfile1.txt

// This requires tip of Go master branch for 1.18; `gotip` is a great tool to
// use.
//

// Run benchmark with
// $ gotip test -bench=. <filename>
package main

import (
	"math/rand"
	"sort"
	"testing"
)

const N = 100_000

type Pair struct {
	A, B int
}

func makeRandomPairs(n int) []*Pair {
	pairs := make([]*Pair, n)
	for i := 0; i < n; i++ {
		pairs[i] = &Pair{ rand.Intn(n), rand.Intn(n) }
	}
	return pairs
}

func TestTest(t *testing.T) {
	pairs := makeRandomPairs(10)
	quickSortFunc_gen(pairs, 0, len(pairs), maxDepth(len(pairs)), func(a, b *Pair) bool { return a.A < b.A })
	for _, pair := range pairs {
		t.Logf("%#v", pair)
	}
}

func BenchmarkSortSlice(b *testing.B) {
	rand.Seed(42)
	for i := 0; i < b.N; i++ {
		b.StopTimer()
		pairs := makeRandomPairs(N)
		b.StartTimer()
		sort.Slice(pairs, func(i, j int) bool { return pairs[i].A < pairs[j].A })
	}
}

func BenchmarkSortGeneric(b *testing.B) {
	rand.Seed(42)
	for i := 0; i < b.N; i++ {
		b.StopTimer()
		pairs := makeRandomPairs(N)
		b.StartTimer()
		quickSortFunc_gen(pairs, 0, len(pairs), maxDepth(len(pairs)), func(a, b *Pair) bool { return a.A < b.A })
	}
}

// These functions are taken from the Go source code of sort.go and
// tweaked to only work on []int, avoiding interfaces and dispatch.
func insertionSort_func(data []int, a, b int) {
	for i := a + 1; i < b; i++ {
		for j := i; j > a && data[j] < data[j-1]; j-- {
			data[j], data[j-1] = data[j-1], data[j]
		}
	}
}

func maxDepth(n int) int {
	var depth int
	for i := n; i > 0; i >>= 1 {
		depth++
	}
	return depth * 2
}

func quickSort_func(data []int, a, b, maxDepth int) {
	for b-a > 12 {
		if maxDepth == 0 {
			heapSort_func(data, a, b)
			return
		}
		maxDepth--
		mlo, mhi := doPivot_func(data, a, b)
		if mlo-a < b-mhi {
			quickSort_func(data, a, mlo, maxDepth)
			a = mhi
		} else {
			quickSort_func(data, mhi, b, maxDepth)
			b = mlo
		}
	}
	if b-a > 1 {
		for i := a + 6; i < b; i++ {
			if data[i] < data[i-6] {
				data[i], data[i-6] = data[i-6], data[i]
			}
		}
		insertionSort_func(data, a, b)
	}
}

func siftDown_func(data []int, lo, hi, first int) {
	root := lo
	for {
		child := 2*root + 1
		if child >= hi {
			break
		}
		if child+1 < hi && data[first+child] < data[first+child+1] {
			child++
		}
		if !(data[first+root] < data[first+child]) {
			return
		}
		data[first+root], data[first+child] = data[first+child], data[first+root]
		root = child
	}
}

func heapSort_func(data []int, a, b int) {
	first := a
	lo := 0
	hi := b - a
	for i := (hi - 1) / 2; i >= 0; i-- {
		siftDown_func(data, i, hi, first)
	}
	for i := hi - 1; i >= 0; i-- {
		data[first], data[first+i] = data[first+i], data[first]
		siftDown_func(data, lo, i, first)
	}
}

func medianOfThree_func(data []int, m1, m0, m2 int) {
	if data[m1] < data[m0] {
		data[m1], data[m0] = data[m0], data[m1]
	}
	if data[m2] < data[m1] {
		data[m2], data[m1] = data[m1], data[m2]
		if data[m1] < data[m0] {
			data[m1], data[m0] = data[m0], data[m1]
		}
	}
}

func doPivot_func(data []int, lo, hi int) (midlo, midhi int) {
	m := int(uint(lo+hi) >> 1)
	if hi-lo > 40 {
		s := (hi - lo) / 8
		medianOfThree_func(data, lo, lo+s, lo+2*s)
		medianOfThree_func(data, m, m-s, m+s)
		medianOfThree_func(data, hi-1, hi-1-s, hi-1-2*s)
	}
	medianOfThree_func(data, lo, m, hi-1)
	pivot := lo
	a, c := lo+1, hi-1
	for ; a < c && data[a] < data[pivot]; a++ {
	}
	b := a
	for {
		for ; b < c && data[pivot] >= data[b]; b++ {
		}
		for ; b < c && data[pivot] < data[c-1]; c-- {
		}
		if b >= c {
			break
		}
		data[b], data[c-1] = data[c-1], data[b]
		b++
		c--
	}
	protect := hi-c < 5
	if !protect && hi-c < (hi-lo)/4 {
		dups := 0
		if data[pivot] >= data[hi-1] {
			data[c], data[hi-1] = data[hi-1], data[c]
			c++
			dups++
		}
		if data[b-1] >= data[pivot] {
			b--
			dups++
		}
		if data[m] >= data[pivot] {
			data[m], data[b-1] = data[b-1], data[m]
			b--
			dups++
		}
		protect = dups > 1
	}
	if protect {
		for {
			for ; a < b && data[b-1] >= data[pivot]; b-- {
			}
			for ; a < b && data[a] < data[pivot]; a++ {
			}
			if a >= b {
				break
			}
			data[a], data[b-1] = data[b-1], data[a]
			a++
			b--
		}
	}
	data[pivot], data[b-1] = data[b-1], data[pivot]
	return b - 1, c
}

func insertionSortFunc_gen[Elem any](data []Elem, a, b int, less func(a, b Elem) bool) {
	for i := a + 1; i < b; i++ {
		for j := i; j > a && less(data[j], data[j-1]); j-- {
			data[j], data[j-1] = data[j-1], data[j]
		}
	}
}

func quickSortFunc_gen[Elem any](data []Elem, a, b, maxDepth int, less func(a, b Elem) bool) {
	for b-a > 12 {
		if maxDepth == 0 {
			heapSortFunc_gen(data, a, b, less)
			return
		}
		maxDepth--
		mlo, mhi := doPivot_gen(data, a, b, less)
		if mlo-a < b-mhi {
			quickSortFunc_gen(data, a, mlo, maxDepth, less)
			a = mhi
		} else {
			quickSortFunc_gen(data, mhi, b, maxDepth, less)
			b = mlo
		}
	}
	if b-a > 1 {
		for i := a + 6; i < b; i++ {
			if less(data[i], data[i-6]) {
				data[i], data[i-6] = data[i-6], data[i]
			}
		}
		insertionSortFunc_gen(data, a, b, less)
	}
}

func siftDown_gen[Elem any](data []Elem, lo, hi, first int, less func(a, b Elem) bool) {
	root := lo
	for {
		child := 2*root + 1
		if child >= hi {
			break
		}
		if child+1 < hi && less(data[first+child], data[first+child+1]) {
			child++
		}
		if !less(data[first+root], data[first+child]) {
			return
		}
		data[first+root], data[first+child] = data[first+child], data[first+root]
		root = child
	}
}

func heapSortFunc_gen[Elem any](data []Elem, a, b int, less func(a, b Elem) bool) {
	first := a
	lo := 0
	hi := b - a
	for i := (hi - 1) / 2; i >= 0; i-- {
		siftDown_gen(data, i, hi, first, less)
	}
	for i := hi - 1; i >= 0; i-- {
		data[first], data[first+i] = data[first+i], data[first]
		siftDown_gen(data, lo, i, first, less)
	}
}

func medianOfThree_gen[Elem any](data []Elem, m1, m0, m2 int, less func(a, b Elem) bool) {
	if less(data[m1], data[m0]) {
		data[m1], data[m0] = data[m0], data[m1]
	}
	if less(data[m2], data[m1]) {
		data[m2], data[m1] = data[m1], data[m2]
		if less(data[m1], data[m0]) {
			data[m1], data[m0] = data[m0], data[m1]
		}
	}
}

func doPivot_gen[Elem any](data []Elem, lo, hi int, less func(a, b Elem) bool) (midlo, midhi int) {
	m := int(uint(lo+hi) >> 1)
	if hi-lo > 40 {
		s := (hi - lo) / 8
		medianOfThree_gen(data, lo, lo+s, lo+2*s, less)
		medianOfThree_gen(data, m, m-s, m+s, less)
		medianOfThree_gen(data, hi-1, hi-1-s, hi-1-2*s, less)
	}
	medianOfThree_gen(data, lo, m, hi-1, less)
	pivot := lo
	a, c := lo+1, hi-1
	for ; a < c && less(data[a], data[pivot]); a++ {
	}
	b := a
	for {
		for ; b < c && !less(data[pivot], data[b]); b++ {
		}
		for ; b < c && less(data[pivot], data[c-1]); c-- {
		}
		if b >= c {
			break
		}
		data[b], data[c-1] = data[c-1], data[b]
		b++
		c--
	}
	protect := hi-c < 5
	if !protect && hi-c < (hi-lo)/4 {
		dups := 0
		if !less(data[pivot], data[hi-1]) {
			data[c], data[hi-1] = data[hi-1], data[c]
			c++
			dups++
		}
		if !less(data[b-1], data[pivot]) {
			b--
			dups++
		}
		if !less(data[m], data[pivot]) {
			data[m], data[b-1] = data[b-1], data[m]
			b--
			dups++
		}
		protect = dups > 1
	}
	if protect {
		for {
			for ; a < b && !less(data[b-1], data[pivot]); b-- {
			}
			for ; a < b && less(data[a], data[pivot]); a++ {
			}
			if a >= b {
				break
			}
			data[a], data[b-1] = data[b-1], data[a]
			a++
			b--
		}
	}
	data[pivot], data[b-1] = data[b-1], data[pivot]
	return b - 1, c
}