Adding upstream version 1.20.14.upstream/1.20.14upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 663 insertions, 0 deletions

diff --git a/src/sort/gen_sort_variants.go b/src/sort/gen_sort_variants.go
new file mode 100644
index 0000000..d738cac
--- /dev/null
+++ b/src/sort/gen_sort_variants.go
@@ -0,0 +1,663 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build ignore
+// +build ignore
+
+// This program is run via "go generate" (via a directive in sort.go)
+// to generate implementation variants of the underlying sorting algorithm.
+// When passed the -generic flag it generates generic variants of sorting;
+// otherwise it generates the non-generic variants used by the sort package.
+
+package main
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"go/format"
+	"log"
+	"os"
+	"text/template"
+)
+
+type Variant struct {
+	// Name is the variant name: should be unique among variants.
+	Name string
+
+	// Path is the file path into which the generator will emit the code for this
+	// variant.
+	Path string
+
+	// Package is the package this code will be emitted into.
+	Package string
+
+	// Imports is the imports needed for this package.
+	Imports string
+
+	// FuncSuffix is appended to all function names in this variant's code. All
+	// suffixes should be unique within a package.
+	FuncSuffix string
+
+	// DataType is the type of the data parameter of functions in this variant's
+	// code.
+	DataType string
+
+	// TypeParam is the optional type parameter for the function.
+	TypeParam string
+
+	// ExtraParam is an extra parameter to pass to the function. Should begin with
+	// ", " to separate from other params.
+	ExtraParam string
+
+	// ExtraArg is an extra argument to pass to calls between functions; typically
+	// it invokes ExtraParam. Should begin with ", " to separate from other args.
+	ExtraArg string
+
+	// Funcs is a map of functions used from within the template. The following
+	// functions are expected to exist:
+	//
+	//    Less (name, i, j):
+	//      emits a comparison expression that checks if the value `name` at
+	//      index `i` is smaller than at index `j`.
+	//
+	//    Swap (name, i, j):
+	//      emits a statement that performs a data swap between elements `i` and
+	//      `j` of the value `name`.
+	Funcs template.FuncMap
+}
+
+func main() {
+	genGeneric := flag.Bool("generic", false, "generate generic versions")
+	flag.Parse()
+
+	if *genGeneric {
+		generate(&Variant{
+			Name:       "generic_ordered",
+			Path:       "zsortordered.go",
+			Package:    "slices",
+			Imports:    "import \"constraints\"\n",
+			FuncSuffix: "Ordered",
+			TypeParam:  "[E constraints.Ordered]",
+			ExtraParam: "",
+			ExtraArg:   "",
+			DataType:   "[]E",
+			Funcs: template.FuncMap{
+				"Less": func(name, i, j string) string {
+					return fmt.Sprintf("(%s[%s] < %s[%s])", name, i, name, j)
+				},
+				"Swap": func(name, i, j string) string {
+					return fmt.Sprintf("%s[%s], %s[%s] = %s[%s], %s[%s]", name, i, name, j, name, j, name, i)
+				},
+			},
+		})
+
+		generate(&Variant{
+			Name:       "generic_func",
+			Path:       "zsortanyfunc.go",
+			Package:    "slices",
+			FuncSuffix: "LessFunc",
+			TypeParam:  "[E any]",
+			ExtraParam: ", less func(a, b E) bool",
+			ExtraArg:   ", less",
+			DataType:   "[]E",
+			Funcs: template.FuncMap{
+				"Less": func(name, i, j string) string {
+					return fmt.Sprintf("less(%s[%s], %s[%s])", name, i, name, j)
+				},
+				"Swap": func(name, i, j string) string {
+					return fmt.Sprintf("%s[%s], %s[%s] = %s[%s], %s[%s]", name, i, name, j, name, j, name, i)
+				},
+			},
+		})
+	} else {
+		generate(&Variant{
+			Name:       "interface",
+			Path:       "zsortinterface.go",
+			Package:    "sort",
+			Imports:    "",
+			FuncSuffix: "",
+			TypeParam:  "",
+			ExtraParam: "",
+			ExtraArg:   "",
+			DataType:   "Interface",
+			Funcs: template.FuncMap{
+				"Less": func(name, i, j string) string {
+					return fmt.Sprintf("%s.Less(%s, %s)", name, i, j)
+				},
+				"Swap": func(name, i, j string) string {
+					return fmt.Sprintf("%s.Swap(%s, %s)", name, i, j)
+				},
+			},
+		})
+
+		generate(&Variant{
+			Name:       "func",
+			Path:       "zsortfunc.go",
+			Package:    "sort",
+			Imports:    "",
+			FuncSuffix: "_func",
+			TypeParam:  "",
+			ExtraParam: "",
+			ExtraArg:   "",
+			DataType:   "lessSwap",
+			Funcs: template.FuncMap{
+				"Less": func(name, i, j string) string {
+					return fmt.Sprintf("%s.Less(%s, %s)", name, i, j)
+				},
+				"Swap": func(name, i, j string) string {
+					return fmt.Sprintf("%s.Swap(%s, %s)", name, i, j)
+				},
+			},
+		})
+	}
+}
+
+// generate generates the code for variant `v` into a file named by `v.Path`.
+func generate(v *Variant) {
+	// Parse templateCode anew for each variant because Parse requires Funcs to be
+	// registered, and it helps type-check the funcs.
+	tmpl, err := template.New("gen").Funcs(v.Funcs).Parse(templateCode)
+	if err != nil {
+		log.Fatal("template Parse:", err)
+	}
+
+	var out bytes.Buffer
+	err = tmpl.Execute(&out, v)
+	if err != nil {
+		log.Fatal("template Execute:", err)
+	}
+
+	formatted, err := format.Source(out.Bytes())
+	if err != nil {
+		log.Fatal("format:", err)
+	}
+
+	if err := os.WriteFile(v.Path, formatted, 0644); err != nil {
+		log.Fatal("WriteFile:", err)
+	}
+}
+
+var templateCode = `// Code generated by gen_sort_variants.go; DO NOT EDIT.
+
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package {{.Package}}
+
+{{.Imports}}
+
+// insertionSort{{.FuncSuffix}} sorts data[a:b] using insertion sort.
+func insertionSort{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a, b int {{.ExtraParam}}) {
+	for i := a + 1; i < b; i++ {
+		for j := i; j > a && {{Less "data" "j" "j-1"}}; j-- {
+			{{Swap "data" "j" "j-1"}}
+		}
+	}
+}
+
+// siftDown{{.FuncSuffix}} implements the heap property on data[lo:hi].
+// first is an offset into the array where the root of the heap lies.
+func siftDown{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, lo, hi, first int {{.ExtraParam}}) {
+	root := lo
+	for {
+		child := 2*root + 1
+		if child >= hi {
+			break
+		}
+		if child+1 < hi && {{Less "data" "first+child" "first+child+1"}} {
+			child++
+		}
+		if !{{Less "data" "first+root" "first+child"}} {
+			return
+		}
+		{{Swap "data" "first+root" "first+child"}}
+		root = child
+	}
+}
+
+func heapSort{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a, b int {{.ExtraParam}}) {
+	first := a
+	lo := 0
+	hi := b - a
+
+	// Build heap with greatest element at top.
+	for i := (hi - 1) / 2; i >= 0; i-- {
+		siftDown{{.FuncSuffix}}(data, i, hi, first {{.ExtraArg}})
+	}
+
+	// Pop elements, largest first, into end of data.
+	for i := hi - 1; i >= 0; i-- {
+		{{Swap "data" "first" "first+i"}}
+		siftDown{{.FuncSuffix}}(data, lo, i, first {{.ExtraArg}})
+	}
+}
+
+// pdqsort{{.FuncSuffix}} sorts data[a:b].
+// The algorithm based on pattern-defeating quicksort(pdqsort), but without the optimizations from BlockQuicksort.
+// pdqsort paper: https://arxiv.org/pdf/2106.05123.pdf
+// C++ implementation: https://github.com/orlp/pdqsort
+// Rust implementation: https://docs.rs/pdqsort/latest/pdqsort/
+// limit is the number of allowed bad (very unbalanced) pivots before falling back to heapsort.
+func pdqsort{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a, b, limit int {{.ExtraParam}}) {
+	const maxInsertion = 12
+
+	var (
+		wasBalanced    = true // whether the last partitioning was reasonably balanced
+		wasPartitioned = true // whether the slice was already partitioned
+	)
+
+	for {
+		length := b - a
+
+		if length <= maxInsertion {
+			insertionSort{{.FuncSuffix}}(data, a, b {{.ExtraArg}})
+			return
+		}
+
+		// Fall back to heapsort if too many bad choices were made.
+		if limit == 0 {
+			heapSort{{.FuncSuffix}}(data, a, b {{.ExtraArg}})
+			return
+		}
+
+		// If the last partitioning was imbalanced, we need to breaking patterns.
+		if !wasBalanced {
+			breakPatterns{{.FuncSuffix}}(data, a, b {{.ExtraArg}})
+			limit--
+		}
+
+		pivot, hint := choosePivot{{.FuncSuffix}}(data, a, b {{.ExtraArg}})
+		if hint == decreasingHint {
+			reverseRange{{.FuncSuffix}}(data, a, b {{.ExtraArg}})
+			// The chosen pivot was pivot-a elements after the start of the array.
+			// After reversing it is pivot-a elements before the end of the array.
+			// The idea came from Rust's implementation.
+			pivot = (b - 1) - (pivot - a)
+			hint = increasingHint
+		}
+
+		// The slice is likely already sorted.
+		if wasBalanced && wasPartitioned && hint == increasingHint {
+			if partialInsertionSort{{.FuncSuffix}}(data, a, b {{.ExtraArg}}) {
+				return
+			}
+		}
+
+		// Probably the slice contains many duplicate elements, partition the slice into
+		// elements equal to and elements greater than the pivot.
+		if a > 0 && !{{Less "data" "a-1" "pivot"}} {
+			mid := partitionEqual{{.FuncSuffix}}(data, a, b, pivot {{.ExtraArg}})
+			a = mid
+			continue
+		}
+
+		mid, alreadyPartitioned := partition{{.FuncSuffix}}(data, a, b, pivot {{.ExtraArg}})
+		wasPartitioned = alreadyPartitioned
+
+		leftLen, rightLen := mid-a, b-mid
+		balanceThreshold := length / 8
+		if leftLen < rightLen {
+			wasBalanced = leftLen >= balanceThreshold
+			pdqsort{{.FuncSuffix}}(data, a, mid, limit {{.ExtraArg}})
+			a = mid + 1
+		} else {
+			wasBalanced = rightLen >= balanceThreshold
+			pdqsort{{.FuncSuffix}}(data, mid+1, b, limit {{.ExtraArg}})
+			b = mid
+		}
+	}
+}
+
+// partition{{.FuncSuffix}} does one quicksort partition.
+// Let p = data[pivot]
+// Moves elements in data[a:b] around, so that data[i]<p and data[j]>=p for i<newpivot and j>newpivot.
+// On return, data[newpivot] = p
+func partition{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a, b, pivot int {{.ExtraParam}}) (newpivot int, alreadyPartitioned bool) {
+	{{Swap "data" "a" "pivot"}}
+	i, j := a+1, b-1 // i and j are inclusive of the elements remaining to be partitioned
+
+	for i <= j && {{Less "data" "i" "a"}} {
+		i++
+	}
+	for i <= j && !{{Less "data" "j" "a"}} {
+		j--
+	}
+	if i > j {
+		{{Swap "data" "j" "a"}}
+		return j, true
+	}
+	{{Swap "data" "i" "j"}}
+	i++
+	j--
+
+	for {
+		for i <= j && {{Less "data" "i" "a"}} {
+			i++
+		}
+		for i <= j && !{{Less "data" "j" "a"}} {
+			j--
+		}
+		if i > j {
+			break
+		}
+		{{Swap "data" "i" "j"}}
+		i++
+		j--
+	}
+	{{Swap "data" "j" "a"}}
+	return j, false
+}
+
+// partitionEqual{{.FuncSuffix}} partitions data[a:b] into elements equal to data[pivot] followed by elements greater than data[pivot].
+// It assumed that data[a:b] does not contain elements smaller than the data[pivot].
+func partitionEqual{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a, b, pivot int {{.ExtraParam}}) (newpivot int) {
+	{{Swap "data" "a" "pivot"}}
+	i, j := a+1, b-1 // i and j are inclusive of the elements remaining to be partitioned
+
+	for {
+		for i <= j && !{{Less "data" "a" "i"}} {
+			i++
+		}
+		for i <= j && {{Less "data" "a" "j"}} {
+			j--
+		}
+		if i > j {
+			break
+		}
+		{{Swap "data" "i" "j"}}
+		i++
+		j--
+	}
+	return i
+}
+
+// partialInsertionSort{{.FuncSuffix}} partially sorts a slice, returns true if the slice is sorted at the end.
+func partialInsertionSort{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a, b int {{.ExtraParam}}) bool {
+	const (
+		maxSteps         = 5  // maximum number of adjacent out-of-order pairs that will get shifted
+		shortestShifting = 50 // don't shift any elements on short arrays
+	)
+	i := a + 1
+	for j := 0; j < maxSteps; j++ {
+		for i < b && !{{Less "data" "i" "i-1"}} {
+			i++
+		}
+
+		if i == b {
+			return true
+		}
+
+		if b-a < shortestShifting {
+			return false
+		}
+
+		{{Swap "data" "i" "i-1"}}
+
+		// Shift the smaller one to the left.
+		if i-a >= 2 {
+			for j := i - 1; j >= 1; j-- {
+				if !{{Less "data" "j" "j-1"}} {
+					break
+				}
+				{{Swap "data" "j" "j-1"}}
+			}
+		}
+		// Shift the greater one to the right.
+		if b-i >= 2 {
+			for j := i + 1; j < b; j++ {
+				if !{{Less "data" "j" "j-1"}} {
+					break
+				}
+				{{Swap "data" "j" "j-1"}}
+			}
+		}
+	}
+	return false
+}
+
+// breakPatterns{{.FuncSuffix}} scatters some elements around in an attempt to break some patterns
+// that might cause imbalanced partitions in quicksort.
+func breakPatterns{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a, b int {{.ExtraParam}}) {
+	length := b - a
+	if length >= 8 {
+		random := xorshift(length)
+		modulus := nextPowerOfTwo(length)
+
+		for idx := a + (length/4)*2 - 1; idx <= a + (length/4)*2 + 1; idx++ {
+			other := int(uint(random.Next()) & (modulus - 1))
+			if other >= length {
+				other -= length
+			}
+			{{Swap "data" "idx" "a+other"}}
+		}
+	}
+}
+
+// choosePivot{{.FuncSuffix}} chooses a pivot in data[a:b].
+//
+// [0,8): chooses a static pivot.
+// [8,shortestNinther): uses the simple median-of-three method.
+// [shortestNinther,∞): uses the Tukey ninther method.
+func choosePivot{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a, b int {{.ExtraParam}}) (pivot int, hint sortedHint) {
+	const (
+		shortestNinther = 50
+		maxSwaps        = 4 * 3
+	)
+
+	l := b - a
+
+	var (
+		swaps int
+		i     = a + l/4*1
+		j     = a + l/4*2
+		k     = a + l/4*3
+	)
+
+	if l >= 8 {
+		if l >= shortestNinther {
+			// Tukey ninther method, the idea came from Rust's implementation.
+			i = medianAdjacent{{.FuncSuffix}}(data, i, &swaps {{.ExtraArg}})
+			j = medianAdjacent{{.FuncSuffix}}(data, j, &swaps {{.ExtraArg}})
+			k = medianAdjacent{{.FuncSuffix}}(data, k, &swaps {{.ExtraArg}})
+		}
+		// Find the median among i, j, k and stores it into j.
+		j = median{{.FuncSuffix}}(data, i, j, k, &swaps {{.ExtraArg}})
+	}
+
+	switch swaps {
+	case 0:
+		return j, increasingHint
+	case maxSwaps:
+		return j, decreasingHint
+	default:
+		return j, unknownHint
+	}
+}
+
+// order2{{.FuncSuffix}} returns x,y where data[x] <= data[y], where x,y=a,b or x,y=b,a.
+func order2{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a, b int, swaps *int {{.ExtraParam}}) (int, int) {
+	if {{Less "data" "b" "a"}} {
+		*swaps++
+		return b, a
+	}
+	return a, b
+}
+
+// median{{.FuncSuffix}} returns x where data[x] is the median of data[a],data[b],data[c], where x is a, b, or c.
+func median{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a, b, c int, swaps *int {{.ExtraParam}}) int {
+	a, b = order2{{.FuncSuffix}}(data, a, b, swaps {{.ExtraArg}})
+	b, c = order2{{.FuncSuffix}}(data, b, c, swaps {{.ExtraArg}})
+	a, b = order2{{.FuncSuffix}}(data, a, b, swaps {{.ExtraArg}})
+	return b
+}
+
+// medianAdjacent{{.FuncSuffix}} finds the median of data[a - 1], data[a], data[a + 1] and stores the index into a.
+func medianAdjacent{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a int, swaps *int {{.ExtraParam}}) int {
+	return median{{.FuncSuffix}}(data, a-1, a, a+1, swaps {{.ExtraArg}})
+}
+
+func reverseRange{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a, b int {{.ExtraParam}}) {
+	i := a
+	j := b - 1
+	for i < j {
+		{{Swap "data" "i" "j"}}
+		i++
+		j--
+	}
+}
+
+func swapRange{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a, b, n int {{.ExtraParam}}) {
+	for i := 0; i < n; i++ {
+		{{Swap "data" "a+i" "b+i"}}
+	}
+}
+
+func stable{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, n int {{.ExtraParam}}) {
+	blockSize := 20 // must be > 0
+	a, b := 0, blockSize
+	for b <= n {
+		insertionSort{{.FuncSuffix}}(data, a, b {{.ExtraArg}})
+		a = b
+		b += blockSize
+	}
+	insertionSort{{.FuncSuffix}}(data, a, n {{.ExtraArg}})
+
+	for blockSize < n {
+		a, b = 0, 2*blockSize
+		for b <= n {
+			symMerge{{.FuncSuffix}}(data, a, a+blockSize, b {{.ExtraArg}})
+			a = b
+			b += 2 * blockSize
+		}
+		if m := a + blockSize; m < n {
+			symMerge{{.FuncSuffix}}(data, a, m, n {{.ExtraArg}})
+		}
+		blockSize *= 2
+	}
+}
+
+// symMerge{{.FuncSuffix}} merges the two sorted subsequences data[a:m] and data[m:b] using
+// the SymMerge algorithm from Pok-Son Kim and Arne Kutzner, "Stable Minimum
+// Storage Merging by Symmetric Comparisons", in Susanne Albers and Tomasz
+// Radzik, editors, Algorithms - ESA 2004, volume 3221 of Lecture Notes in
+// Computer Science, pages 714-723. Springer, 2004.
+//
+// Let M = m-a and N = b-n. Wolog M < N.
+// The recursion depth is bound by ceil(log(N+M)).
+// The algorithm needs O(M*log(N/M + 1)) calls to data.Less.
+// The algorithm needs O((M+N)*log(M)) calls to data.Swap.
+//
+// The paper gives O((M+N)*log(M)) as the number of assignments assuming a
+// rotation algorithm which uses O(M+N+gcd(M+N)) assignments. The argumentation
+// in the paper carries through for Swap operations, especially as the block
+// swapping rotate uses only O(M+N) Swaps.
+//
+// symMerge assumes non-degenerate arguments: a < m && m < b.
+// Having the caller check this condition eliminates many leaf recursion calls,
+// which improves performance.
+func symMerge{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a, m, b int {{.ExtraParam}}) {
+	// Avoid unnecessary recursions of symMerge
+	// by direct insertion of data[a] into data[m:b]
+	// if data[a:m] only contains one element.
+	if m-a == 1 {
+		// Use binary search to find the lowest index i
+		// such that data[i] >= data[a] for m <= i < b.
+		// Exit the search loop with i == b in case no such index exists.
+		i := m
+		j := b
+		for i < j {
+			h := int(uint(i+j) >> 1)
+			if {{Less "data" "h" "a"}} {
+				i = h + 1
+			} else {
+				j = h
+			}
+		}
+		// Swap values until data[a] reaches the position before i.
+		for k := a; k < i-1; k++ {
+			{{Swap "data" "k" "k+1"}}
+		}
+		return
+	}
+
+	// Avoid unnecessary recursions of symMerge
+	// by direct insertion of data[m] into data[a:m]
+	// if data[m:b] only contains one element.
+	if b-m == 1 {
+		// Use binary search to find the lowest index i
+		// such that data[i] > data[m] for a <= i < m.
+		// Exit the search loop with i == m in case no such index exists.
+		i := a
+		j := m
+		for i < j {
+			h := int(uint(i+j) >> 1)
+			if !{{Less "data" "m" "h"}} {
+				i = h + 1
+			} else {
+				j = h
+			}
+		}
+		// Swap values until data[m] reaches the position i.
+		for k := m; k > i; k-- {
+			{{Swap "data" "k" "k-1"}}
+		}
+		return
+	}
+
+	mid := int(uint(a+b) >> 1)
+	n := mid + m
+	var start, r int
+	if m > mid {
+		start = n - b
+		r = mid
+	} else {
+		start = a
+		r = m
+	}
+	p := n - 1
+
+	for start < r {
+		c := int(uint(start+r) >> 1)
+		if !{{Less "data" "p-c" "c"}} {
+			start = c + 1
+		} else {
+			r = c
+		}
+	}
+
+	end := n - start
+	if start < m && m < end {
+		rotate{{.FuncSuffix}}(data, start, m, end {{.ExtraArg}})
+	}
+	if a < start && start < mid {
+		symMerge{{.FuncSuffix}}(data, a, start, mid {{.ExtraArg}})
+	}
+	if mid < end && end < b {
+		symMerge{{.FuncSuffix}}(data, mid, end, b {{.ExtraArg}})
+	}
+}
+
+// rotate{{.FuncSuffix}} rotates two consecutive blocks u = data[a:m] and v = data[m:b] in data:
+// Data of the form 'x u v y' is changed to 'x v u y'.
+// rotate performs at most b-a many calls to data.Swap,
+// and it assumes non-degenerate arguments: a < m && m < b.
+func rotate{{.FuncSuffix}}{{.TypeParam}}(data {{.DataType}}, a, m, b int {{.ExtraParam}}) {
+	i := m - a
+	j := b - m
+
+	for i != j {
+		if i > j {
+			swapRange{{.FuncSuffix}}(data, m-i, m, j {{.ExtraArg}})
+			i -= j
+		} else {
+			swapRange{{.FuncSuffix}}(data, m-i, m+j-i, i {{.ExtraArg}})
+			j -= i
+		}
+	}
+	// i == j
+	swapRange{{.FuncSuffix}}(data, m-i, m, i {{.ExtraArg}})
+}
+`