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// 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 slices
// insertionSortLessFunc sorts data[a:b] using insertion sort.
func insertionSortLessFunc[E any](data []E, a, b int, less func(a, b E) 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]
}
}
}
// siftDownLessFunc implements the heap property on data[lo:hi].
// first is an offset into the array where the root of the heap lies.
func siftDownLessFunc[E any](data []E, lo, hi, first int, less func(a, b E) 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 heapSortLessFunc[E any](data []E, a, b int, less func(a, b E) bool) {
first := a
lo := 0
hi := b - a
// Build heap with greatest element at top.
for i := (hi - 1) / 2; i >= 0; i-- {
siftDownLessFunc(data, i, hi, first, less)
}
// Pop elements, largest first, into end of data.
for i := hi - 1; i >= 0; i-- {
data[first], data[first+i] = data[first+i], data[first]
siftDownLessFunc(data, lo, i, first, less)
}
}
// pdqsortLessFunc 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 pdqsortLessFunc[E any](data []E, a, b, limit int, less func(a, b E) bool) {
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 {
insertionSortLessFunc(data, a, b, less)
return
}
// Fall back to heapsort if too many bad choices were made.
if limit == 0 {
heapSortLessFunc(data, a, b, less)
return
}
// If the last partitioning was imbalanced, we need to breaking patterns.
if !wasBalanced {
breakPatternsLessFunc(data, a, b, less)
limit--
}
pivot, hint := choosePivotLessFunc(data, a, b, less)
if hint == decreasingHint {
reverseRangeLessFunc(data, a, b, less)
// 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 partialInsertionSortLessFunc(data, a, b, less) {
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], data[pivot]) {
mid := partitionEqualLessFunc(data, a, b, pivot, less)
a = mid
continue
}
mid, alreadyPartitioned := partitionLessFunc(data, a, b, pivot, less)
wasPartitioned = alreadyPartitioned
leftLen, rightLen := mid-a, b-mid
balanceThreshold := length / 8
if leftLen < rightLen {
wasBalanced = leftLen >= balanceThreshold
pdqsortLessFunc(data, a, mid, limit, less)
a = mid + 1
} else {
wasBalanced = rightLen >= balanceThreshold
pdqsortLessFunc(data, mid+1, b, limit, less)
b = mid
}
}
}
// partitionLessFunc 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 partitionLessFunc[E any](data []E, a, b, pivot int, less func(a, b E) bool) (newpivot int, alreadyPartitioned bool) {
data[a], data[pivot] = data[pivot], data[a]
i, j := a+1, b-1 // i and j are inclusive of the elements remaining to be partitioned
for i <= j && less(data[i], data[a]) {
i++
}
for i <= j && !less(data[j], data[a]) {
j--
}
if i > j {
data[j], data[a] = data[a], data[j]
return j, true
}
data[i], data[j] = data[j], data[i]
i++
j--
for {
for i <= j && less(data[i], data[a]) {
i++
}
for i <= j && !less(data[j], data[a]) {
j--
}
if i > j {
break
}
data[i], data[j] = data[j], data[i]
i++
j--
}
data[j], data[a] = data[a], data[j]
return j, false
}
// partitionEqualLessFunc 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 partitionEqualLessFunc[E any](data []E, a, b, pivot int, less func(a, b E) bool) (newpivot int) {
data[a], data[pivot] = data[pivot], data[a]
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], data[i]) {
i++
}
for i <= j && less(data[a], data[j]) {
j--
}
if i > j {
break
}
data[i], data[j] = data[j], data[i]
i++
j--
}
return i
}
// partialInsertionSortLessFunc partially sorts a slice, returns true if the slice is sorted at the end.
func partialInsertionSortLessFunc[E any](data []E, a, b int, less func(a, b E) bool) 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], data[i-1]) {
i++
}
if i == b {
return true
}
if b-a < shortestShifting {
return false
}
data[i], data[i-1] = data[i-1], data[i]
// Shift the smaller one to the left.
if i-a >= 2 {
for j := i - 1; j >= 1; j-- {
if !less(data[j], data[j-1]) {
break
}
data[j], data[j-1] = data[j-1], data[j]
}
}
// Shift the greater one to the right.
if b-i >= 2 {
for j := i + 1; j < b; j++ {
if !less(data[j], data[j-1]) {
break
}
data[j], data[j-1] = data[j-1], data[j]
}
}
}
return false
}
// breakPatternsLessFunc scatters some elements around in an attempt to break some patterns
// that might cause imbalanced partitions in quicksort.
func breakPatternsLessFunc[E any](data []E, a, b int, less func(a, b E) bool) {
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
}
data[idx], data[a+other] = data[a+other], data[idx]
}
}
}
// choosePivotLessFunc 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 choosePivotLessFunc[E any](data []E, a, b int, less func(a, b E) bool) (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 = medianAdjacentLessFunc(data, i, &swaps, less)
j = medianAdjacentLessFunc(data, j, &swaps, less)
k = medianAdjacentLessFunc(data, k, &swaps, less)
}
// Find the median among i, j, k and stores it into j.
j = medianLessFunc(data, i, j, k, &swaps, less)
}
switch swaps {
case 0:
return j, increasingHint
case maxSwaps:
return j, decreasingHint
default:
return j, unknownHint
}
}
// order2LessFunc returns x,y where data[x] <= data[y], where x,y=a,b or x,y=b,a.
func order2LessFunc[E any](data []E, a, b int, swaps *int, less func(a, b E) bool) (int, int) {
if less(data[b], data[a]) {
*swaps++
return b, a
}
return a, b
}
// medianLessFunc returns x where data[x] is the median of data[a],data[b],data[c], where x is a, b, or c.
func medianLessFunc[E any](data []E, a, b, c int, swaps *int, less func(a, b E) bool) int {
a, b = order2LessFunc(data, a, b, swaps, less)
b, c = order2LessFunc(data, b, c, swaps, less)
a, b = order2LessFunc(data, a, b, swaps, less)
return b
}
// medianAdjacentLessFunc finds the median of data[a - 1], data[a], data[a + 1] and stores the index into a.
func medianAdjacentLessFunc[E any](data []E, a int, swaps *int, less func(a, b E) bool) int {
return medianLessFunc(data, a-1, a, a+1, swaps, less)
}
func reverseRangeLessFunc[E any](data []E, a, b int, less func(a, b E) bool) {
i := a
j := b - 1
for i < j {
data[i], data[j] = data[j], data[i]
i++
j--
}
}
func swapRangeLessFunc[E any](data []E, a, b, n int, less func(a, b E) bool) {
for i := 0; i < n; i++ {
data[a+i], data[b+i] = data[b+i], data[a+i]
}
}
func stableLessFunc[E any](data []E, n int, less func(a, b E) bool) {
blockSize := 20 // must be > 0
a, b := 0, blockSize
for b <= n {
insertionSortLessFunc(data, a, b, less)
a = b
b += blockSize
}
insertionSortLessFunc(data, a, n, less)
for blockSize < n {
a, b = 0, 2*blockSize
for b <= n {
symMergeLessFunc(data, a, a+blockSize, b, less)
a = b
b += 2 * blockSize
}
if m := a + blockSize; m < n {
symMergeLessFunc(data, a, m, n, less)
}
blockSize *= 2
}
}
// symMergeLessFunc 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 symMergeLessFunc[E any](data []E, a, m, b int, less func(a, b E) bool) {
// 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], data[a]) {
i = h + 1
} else {
j = h
}
}
// Swap values until data[a] reaches the position before i.
for k := a; k < i-1; k++ {
data[k], data[k+1] = data[k+1], data[k]
}
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], data[h]) {
i = h + 1
} else {
j = h
}
}
// Swap values until data[m] reaches the position i.
for k := m; k > i; k-- {
data[k], data[k-1] = data[k-1], data[k]
}
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], data[c]) {
start = c + 1
} else {
r = c
}
}
end := n - start
if start < m && m < end {
rotateLessFunc(data, start, m, end, less)
}
if a < start && start < mid {
symMergeLessFunc(data, a, start, mid, less)
}
if mid < end && end < b {
symMergeLessFunc(data, mid, end, b, less)
}
}
// rotateLessFunc 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 rotateLessFunc[E any](data []E, a, m, b int, less func(a, b E) bool) {
i := m - a
j := b - m
for i != j {
if i > j {
swapRangeLessFunc(data, m-i, m, j, less)
i -= j
} else {
swapRangeLessFunc(data, m-i, m+j-i, i, less)
j -= i
}
}
// i == j
swapRangeLessFunc(data, m-i, m, i, less)
}