github.com/Inphi/go-ethereum@v1.9.7/common/prque/sstack.go (about)

     1  // CookieJar - A contestant's algorithm toolbox
     2  // Copyright (c) 2013 Peter Szilagyi. All rights reserved.
     3  //
     4  // CookieJar is dual licensed: use of this source code is governed by a BSD
     5  // license that can be found in the LICENSE file. Alternatively, the CookieJar
     6  // toolbox may be used in accordance with the terms and conditions contained
     7  // in a signed written agreement between you and the author(s).
     8  
     9  // This is a duplicated and slightly modified version of "gopkg.in/karalabe/cookiejar.v2/collections/prque".
    10  
    11  package prque
    12  
    13  // The size of a block of data
    14  const blockSize = 4096
    15  
    16  // A prioritized item in the sorted stack.
    17  //
    18  // Note: priorities can "wrap around" the int64 range, a comes before b if (a.priority - b.priority) > 0.
    19  // The difference between the lowest and highest priorities in the queue at any point should be less than 2^63.
    20  type item struct {
    21  	value    interface{}
    22  	priority int64
    23  }
    24  
    25  // SetIndexCallback is called when the element is moved to a new index.
    26  // Providing SetIndexCallback is optional, it is needed only if the application needs
    27  // to delete elements other than the top one.
    28  type SetIndexCallback func(data interface{}, index int)
    29  
    30  // Internal sortable stack data structure. Implements the Push and Pop ops for
    31  // the stack (heap) functionality and the Len, Less and Swap methods for the
    32  // sortability requirements of the heaps.
    33  type sstack struct {
    34  	setIndex SetIndexCallback
    35  	size     int
    36  	capacity int
    37  	offset   int
    38  
    39  	blocks [][]*item
    40  	active []*item
    41  }
    42  
    43  // Creates a new, empty stack.
    44  func newSstack(setIndex SetIndexCallback) *sstack {
    45  	result := new(sstack)
    46  	result.setIndex = setIndex
    47  	result.active = make([]*item, blockSize)
    48  	result.blocks = [][]*item{result.active}
    49  	result.capacity = blockSize
    50  	return result
    51  }
    52  
    53  // Pushes a value onto the stack, expanding it if necessary. Required by
    54  // heap.Interface.
    55  func (s *sstack) Push(data interface{}) {
    56  	if s.size == s.capacity {
    57  		s.active = make([]*item, blockSize)
    58  		s.blocks = append(s.blocks, s.active)
    59  		s.capacity += blockSize
    60  		s.offset = 0
    61  	} else if s.offset == blockSize {
    62  		s.active = s.blocks[s.size/blockSize]
    63  		s.offset = 0
    64  	}
    65  	if s.setIndex != nil {
    66  		s.setIndex(data.(*item).value, s.size)
    67  	}
    68  	s.active[s.offset] = data.(*item)
    69  	s.offset++
    70  	s.size++
    71  }
    72  
    73  // Pops a value off the stack and returns it. Currently no shrinking is done.
    74  // Required by heap.Interface.
    75  func (s *sstack) Pop() (res interface{}) {
    76  	s.size--
    77  	s.offset--
    78  	if s.offset < 0 {
    79  		s.offset = blockSize - 1
    80  		s.active = s.blocks[s.size/blockSize]
    81  	}
    82  	res, s.active[s.offset] = s.active[s.offset], nil
    83  	if s.setIndex != nil {
    84  		s.setIndex(res.(*item).value, -1)
    85  	}
    86  	return
    87  }
    88  
    89  // Returns the length of the stack. Required by sort.Interface.
    90  func (s *sstack) Len() int {
    91  	return s.size
    92  }
    93  
    94  // Compares the priority of two elements of the stack (higher is first).
    95  // Required by sort.Interface.
    96  func (s *sstack) Less(i, j int) bool {
    97  	return (s.blocks[i/blockSize][i%blockSize].priority - s.blocks[j/blockSize][j%blockSize].priority) > 0
    98  }
    99  
   100  // Swaps two elements in the stack. Required by sort.Interface.
   101  func (s *sstack) Swap(i, j int) {
   102  	ib, io, jb, jo := i/blockSize, i%blockSize, j/blockSize, j%blockSize
   103  	a, b := s.blocks[jb][jo], s.blocks[ib][io]
   104  	if s.setIndex != nil {
   105  		s.setIndex(a.value, i)
   106  		s.setIndex(b.value, j)
   107  	}
   108  	s.blocks[ib][io], s.blocks[jb][jo] = a, b
   109  }
   110  
   111  // Resets the stack, effectively clearing its contents.
   112  func (s *sstack) Reset() {
   113  	*s = *newSstack(s.setIndex)
   114  }