github.com/cockroachdb/pebble@v1.1.1-0.20240513155919-3622ade60459/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 mergingIterHeap struct {
     8  	cmp     Compare
     9  	reverse bool
    10  	items   []*mergingIterLevel
    11  }
    12  
    13  func (h *mergingIterHeap) len() int {
    14  	return len(h.items)
    15  }
    16  
    17  func (h *mergingIterHeap) clear() {
    18  	h.items = h.items[:0]
    19  }
    20  
    21  func (h *mergingIterHeap) less(i, j int) bool {
    22  	ikey, jkey := h.items[i].iterKey, h.items[j].iterKey
    23  	if c := h.cmp(ikey.UserKey, jkey.UserKey); c != 0 {
    24  		if h.reverse {
    25  			return c > 0
    26  		}
    27  		return c < 0
    28  	}
    29  	if h.reverse {
    30  		return ikey.Trailer < jkey.Trailer
    31  	}
    32  	return ikey.Trailer > jkey.Trailer
    33  }
    34  
    35  func (h *mergingIterHeap) swap(i, j int) {
    36  	h.items[i], h.items[j] = h.items[j], h.items[i]
    37  }
    38  
    39  // init, fix, up and down are copied from the go stdlib.
    40  func (h *mergingIterHeap) init() {
    41  	// heapify
    42  	n := h.len()
    43  	for i := n/2 - 1; i >= 0; i-- {
    44  		h.down(i, n)
    45  	}
    46  }
    47  
    48  func (h *mergingIterHeap) fix(i int) {
    49  	if !h.down(i, h.len()) {
    50  		h.up(i)
    51  	}
    52  }
    53  
    54  func (h *mergingIterHeap) pop() *mergingIterLevel {
    55  	n := h.len() - 1
    56  	h.swap(0, n)
    57  	h.down(0, n)
    58  	item := h.items[n]
    59  	h.items = h.items[:n]
    60  	return item
    61  }
    62  
    63  func (h *mergingIterHeap) up(j int) {
    64  	for {
    65  		i := (j - 1) / 2 // parent
    66  		if i == j || !h.less(j, i) {
    67  			break
    68  		}
    69  		h.swap(i, j)
    70  		j = i
    71  	}
    72  }
    73  
    74  func (h *mergingIterHeap) down(i0, n int) bool {
    75  	i := i0
    76  	for {
    77  		j1 := 2*i + 1
    78  		if j1 >= n || j1 < 0 { // j1 < 0 after int overflow
    79  			break
    80  		}
    81  		j := j1 // left child
    82  		if j2 := j1 + 1; j2 < n && h.less(j2, j1) {
    83  			j = j2 // = 2*i + 2  // right child
    84  		}
    85  		if !h.less(j, i) {
    86  			break
    87  		}
    88  		h.swap(i, j)
    89  		i = j
    90  	}
    91  	return i > i0
    92  }