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// Copyright 2019 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.
//go:build !go1.12
// +build !go1.12
package span
import (
"go/token"
)
// lineStart is the pre-Go 1.12 version of (*token.File).LineStart. For Go
// versions <= 1.11, we borrow logic from the analysisutil package.
// TODO(rstambler): Delete this file when we no longer support Go 1.11.
func lineStart(f *token.File, line int) token.Pos {
// Use binary search to find the start offset of this line.
min := 0 // inclusive
max := f.Size() // exclusive
for {
offset := (min + max) / 2
pos := f.Pos(offset)
posn := f.Position(pos)
if posn.Line == line {
return pos - (token.Pos(posn.Column) - 1)
}
if min+1 >= max {
return token.NoPos
}
if posn.Line < line {
min = offset
} else {
max = offset
}
}
}
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