sparsemappos.go

     1  // Copyright 2022 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package ssa
     6  
     7  import "cmd/internal/src"
     8  
     9  // from https://research.swtch.com/sparse
    10  // in turn, from Briggs and Torczon
    11  
    12  type sparseEntryPos struct {
    13  	key ID
    14  	val int32
    15  	pos src.XPos
    16  }
    17  
    18  type sparseMapPos struct {
    19  	dense  []sparseEntryPos
    20  	sparse []int32
    21  }
    22  
    23  // newSparseMapPos returns a sparseMapPos that can map
    24  // integers between 0 and n-1 to the pair <int32,src.XPos>.
    25  func newSparseMapPos(n int) *sparseMapPos {
    26  	return &sparseMapPos{dense: nil, sparse: make([]int32, n)}
    27  }
    28  
    29  func (s *sparseMapPos) cap() int {
    30  	return len(s.sparse)
    31  }
    32  
    33  func (s *sparseMapPos) size() int {
    34  	return len(s.dense)
    35  }
    36  
    37  func (s *sparseMapPos) contains(k ID) bool {
    38  	i := s.sparse[k]
    39  	return i < int32(len(s.dense)) && s.dense[i].key == k
    40  }
    41  
    42  // get returns the value for key k, or -1 if k does
    43  // not appear in the map.
    44  func (s *sparseMapPos) get(k ID) int32 {
    45  	i := s.sparse[k]
    46  	if i < int32(len(s.dense)) && s.dense[i].key == k {
    47  		return s.dense[i].val
    48  	}
    49  	return -1
    50  }
    51  
    52  func (s *sparseMapPos) set(k ID, v int32, a src.XPos) {
    53  	i := s.sparse[k]
    54  	if i < int32(len(s.dense)) && s.dense[i].key == k {
    55  		s.dense[i].val = v
    56  		s.dense[i].pos = a
    57  		return
    58  	}
    59  	s.dense = append(s.dense, sparseEntryPos{k, v, a})
    60  	s.sparse[k] = int32(len(s.dense)) - 1
    61  }
    62  
    63  func (s *sparseMapPos) remove(k ID) {
    64  	i := s.sparse[k]
    65  	if i < int32(len(s.dense)) && s.dense[i].key == k {
    66  		y := s.dense[len(s.dense)-1]
    67  		s.dense[i] = y
    68  		s.sparse[y.key] = i
    69  		s.dense = s.dense[:len(s.dense)-1]
    70  	}
    71  }
    72  
    73  func (s *sparseMapPos) clear() {
    74  	s.dense = s.dense[:0]
    75  }
    76  
    77  func (s *sparseMapPos) contents() []sparseEntryPos {
    78  	return s.dense
    79  }
    80
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