github.com/petermattis/pebble@v0.0.0-20190905164901-ab51a2166067/merging_iter_heap.go (about)

     1  // Copyright 2018 The LevelDB-Go and Pebble Authors. All rights reserved. Use
     2  // of this source code is governed by a BSD-style license that can be found in
     3  // the LICENSE file.
     4  
     5  package pebble
     6  
     7  type mergingIterItem struct {
     8  	index int
     9  	key   InternalKey
    10  	value []byte
    11  }
    12  
    13  type mergingIterHeap struct {
    14  	cmp     Compare
    15  	reverse bool
    16  	items   []mergingIterItem
    17  }
    18  
    19  func (h *mergingIterHeap) len() int {
    20  	return len(h.items)
    21  }
    22  
    23  func (h *mergingIterHeap) less(i, j int) bool {
    24  	ikey, jkey := h.items[i].key, h.items[j].key
    25  	if c := h.cmp(ikey.UserKey, jkey.UserKey); c != 0 {
    26  		if h.reverse {
    27  			return c > 0
    28  		}
    29  		return c < 0
    30  	}
    31  	if h.reverse {
    32  		return ikey.Trailer < jkey.Trailer
    33  	}
    34  	return ikey.Trailer > jkey.Trailer
    35  }
    36  
    37  func (h *mergingIterHeap) swap(i, j int) {
    38  	h.items[i], h.items[j] = h.items[j], h.items[i]
    39  }
    40  
    41  // init, fix, up and down are copied from the go stdlib.
    42  func (h *mergingIterHeap) init() {
    43  	// heapify
    44  	n := h.len()
    45  	for i := n/2 - 1; i >= 0; i-- {
    46  		h.down(i, n)
    47  	}
    48  }
    49  
    50  func (h *mergingIterHeap) fix(i int) {
    51  	if !h.down(i, h.len()) {
    52  		h.up(i)
    53  	}
    54  }
    55  
    56  func (h *mergingIterHeap) pop() *mergingIterItem {
    57  	n := h.len() - 1
    58  	h.swap(0, n)
    59  	h.down(0, n)
    60  	item := &h.items[n]
    61  	h.items = h.items[:n]
    62  	return item
    63  }
    64  
    65  func (h *mergingIterHeap) up(j int) {
    66  	for {
    67  		i := (j - 1) / 2 // parent
    68  		if i == j || !h.less(j, i) {
    69  			break
    70  		}
    71  		h.swap(i, j)
    72  		j = i
    73  	}
    74  }
    75  
    76  func (h *mergingIterHeap) down(i0, n int) bool {
    77  	i := i0
    78  	for {
    79  		j1 := 2*i + 1
    80  		if j1 >= n || j1 < 0 { // j1 < 0 after int overflow
    81  			break
    82  		}
    83  		j := j1 // left child
    84  		if j2 := j1 + 1; j2 < n && h.less(j2, j1) {
    85  			j = j2 // = 2*i + 2  // right child
    86  		}
    87  		if !h.less(j, i) {
    88  			break
    89  		}
    90  		h.swap(i, j)
    91  		i = j
    92  	}
    93  	return i > i0
    94  }