plugeth/common/prque/sstack.go

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// CookieJar - A contestant's algorithm toolbox
// Copyright (c) 2013 Peter Szilagyi. All rights reserved.
//
// CookieJar is dual licensed: use of this source code is governed by a BSD
// license that can be found in the LICENSE file. Alternatively, the CookieJar
// toolbox may be used in accordance with the terms and conditions contained
// in a signed written agreement between you and the author(s).
// This is a duplicated and slightly modified version of "gopkg.in/karalabe/cookiejar.v2/collections/prque".
package prque
import "golang.org/x/exp/constraints"
// The size of a block of data
const blockSize = 4096
// A prioritized item in the sorted stack.
type item[P constraints.Ordered, V any] struct {
value V
priority P
}
// SetIndexCallback is called when the element is moved to a new index.
// Providing SetIndexCallback is optional, it is needed only if the application needs
// to delete elements other than the top one.
type SetIndexCallback[V any] func(data V, index int)
// Internal sortable stack data structure. Implements the Push and Pop ops for
// the stack (heap) functionality and the Len, Less and Swap methods for the
// sortability requirements of the heaps.
type sstack[P constraints.Ordered, V any] struct {
setIndex SetIndexCallback[V]
size int
capacity int
offset int
blocks [][]*item[P, V]
active []*item[P, V]
}
// Creates a new, empty stack.
func newSstack[P constraints.Ordered, V any](setIndex SetIndexCallback[V]) *sstack[P, V] {
result := new(sstack[P, V])
result.setIndex = setIndex
result.active = make([]*item[P, V], blockSize)
result.blocks = [][]*item[P, V]{result.active}
result.capacity = blockSize
return result
}
// Pushes a value onto the stack, expanding it if necessary. Required by
// heap.Interface.
func (s *sstack[P, V]) Push(data any) {
if s.size == s.capacity {
s.active = make([]*item[P, V], blockSize)
s.blocks = append(s.blocks, s.active)
s.capacity += blockSize
s.offset = 0
} else if s.offset == blockSize {
s.active = s.blocks[s.size/blockSize]
s.offset = 0
}
if s.setIndex != nil {
s.setIndex(data.(*item[P, V]).value, s.size)
}
s.active[s.offset] = data.(*item[P, V])
s.offset++
s.size++
}
// Pops a value off the stack and returns it. Currently no shrinking is done.
// Required by heap.Interface.
func (s *sstack[P, V]) Pop() (res any) {
s.size--
s.offset--
if s.offset < 0 {
s.offset = blockSize - 1
s.active = s.blocks[s.size/blockSize]
}
res, s.active[s.offset] = s.active[s.offset], nil
if s.setIndex != nil {
s.setIndex(res.(*item[P, V]).value, -1)
}
return
}
// Returns the length of the stack. Required by sort.Interface.
func (s *sstack[P, V]) Len() int {
return s.size
}
// Compares the priority of two elements of the stack (higher is first).
// Required by sort.Interface.
func (s *sstack[P, V]) Less(i, j int) bool {
return s.blocks[i/blockSize][i%blockSize].priority > s.blocks[j/blockSize][j%blockSize].priority
}
// Swaps two elements in the stack. Required by sort.Interface.
func (s *sstack[P, V]) Swap(i, j int) {
ib, io, jb, jo := i/blockSize, i%blockSize, j/blockSize, j%blockSize
a, b := s.blocks[jb][jo], s.blocks[ib][io]
if s.setIndex != nil {
s.setIndex(a.value, i)
s.setIndex(b.value, j)
}
s.blocks[ib][io], s.blocks[jb][jo] = a, b
}
// Resets the stack, effectively clearing its contents.
func (s *sstack[P, V]) Reset() {
*s = *newSstack[P, V](s.setIndex)
}