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Source file src/cmd/internal/src/xpos.go

Documentation: cmd/internal/src

     1  // Copyright 2016 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  // This file implements the compressed encoding of source
     6  // positions using a lookup table.
     7  
     8  package src
     9  
    10  // XPos is a more compact representation of Pos.
    11  type XPos struct {
    12  	index int32
    13  	lico
    14  }
    15  
    16  // NoXPos is a valid unknown position.
    17  var NoXPos XPos
    18  
    19  // IsKnown reports whether the position p is known.
    20  // XPos.IsKnown() matches Pos.IsKnown() for corresponding
    21  // positions.
    22  func (p XPos) IsKnown() bool {
    23  	return p.index != 0 || p.Line() != 0
    24  }
    25  
    26  // Before reports whether the position p comes before q in the source.
    27  // For positions with different bases, ordering is by base index.
    28  func (p XPos) Before(q XPos) bool {
    29  	n, m := p.index, q.index
    30  	return n < m || n == m && p.lico < q.lico
    31  }
    32  
    33  // After reports whether the position p comes after q in the source.
    34  // For positions with different bases, ordering is by base index.
    35  func (p XPos) After(q XPos) bool {
    36  	n, m := p.index, q.index
    37  	return n > m || n == m && p.lico > q.lico
    38  }
    39  
    40  // A PosTable tracks Pos -> XPos conversions and vice versa.
    41  // Its zero value is a ready-to-use PosTable.
    42  type PosTable struct {
    43  	baseList []*PosBase
    44  	indexMap map[*PosBase]int
    45  }
    46  
    47  // XPos returns the corresponding XPos for the given pos,
    48  // adding pos to t if necessary.
    49  func (t *PosTable) XPos(pos Pos) XPos {
    50  	m := t.indexMap
    51  	if m == nil {
    52  		// Create new list and map and populate with nil
    53  		// base so that NoPos always gets index 0.
    54  		t.baseList = append(t.baseList, nil)
    55  		m = map[*PosBase]int{nil: 0}
    56  		t.indexMap = m
    57  	}
    58  	i, ok := m[pos.base]
    59  	if !ok {
    60  		i = len(t.baseList)
    61  		t.baseList = append(t.baseList, pos.base)
    62  		t.indexMap[pos.base] = i
    63  	}
    64  	return XPos{int32(i), pos.lico}
    65  }
    66  
    67  // Pos returns the corresponding Pos for the given p.
    68  // If p cannot be translated via t, the function panics.
    69  func (t *PosTable) Pos(p XPos) Pos {
    70  	var base *PosBase
    71  	if p.index != 0 {
    72  		base = t.baseList[p.index]
    73  	}
    74  	return Pos{base, p.lico}
    75  }
    76  

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