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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
/*
* Line tables
*/
package gosym
import "encoding/binary"
type LineTable struct {
Data []byte
PC uint64
Line int
}
// TODO(rsc): Need to pull in quantum from architecture definition.
const quantum = 1
func (t *LineTable) parse(targetPC uint64, targetLine int) (b []byte, pc uint64, line int) {
// The PC/line table can be thought of as a sequence of
// <pc update>* <line update>
// batches. Each update batch results in a (pc, line) pair,
// where line applies to every PC from pc up to but not
// including the pc of the next pair.
//
// Here we process each update individually, which simplifies
// the code, but makes the corner cases more confusing.
b, pc, line = t.Data, t.PC, t.Line
for pc <= targetPC && line != targetLine && len(b) > 0 {
code := b[0]
b = b[1:]
switch {
case code == 0:
if len(b) < 4 {
b = b[0:0]
break
}
val := binary.BigEndian.Uint32(b)
b = b[4:]
line += int(val)
case code <= 64:
line += int(code)
case code <= 128:
line -= int(code - 64)
default:
pc += quantum * uint64(code-128)
continue
}
pc += quantum
}
return b, pc, line
}
func (t *LineTable) slice(pc uint64) *LineTable {
data, pc, line := t.parse(pc, -1)
return &LineTable{data, pc, line}
}
func (t *LineTable) PCToLine(pc uint64) int {
_, _, line := t.parse(pc, -1)
return line
}
func (t *LineTable) LineToPC(line int, maxpc uint64) uint64 {
_, pc, line1 := t.parse(maxpc, line)
if line1 != line {
return 0
}
// Subtract quantum from PC to account for post-line increment
return pc - quantum
}
// NewLineTable returns a new PC/line table
// corresponding to the encoded data.
// Text must be the start address of the
// corresponding text segment.
func NewLineTable(data []byte, text uint64) *LineTable {
return &LineTable{data, text, 0}
}
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