You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: util.go
    path of file: ./repos/gccrs/libgo/go/golang.org/x/tools/go/analysis/passes/internal/analysisutil
    
    the code of the file until where you have to start completion: // Copyright 2018 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.

// Package analysisutil defines various helper functions
// used by two or more packages beneath go/analysis.
package analysisutil

import (
	"bytes"
	"go/ast"
	"go/printer"
	"go/token"
	"go/types"
	"io/ioutil"
)

// Format returns a string representation of the expression.
func Format(fset *token.FileSet, x ast.Expr) string {
	var b byt
    
func LineStart(f *token.File, line int) token.Pos {
	// Use binary search to find the start offset of this line.
	//
	// TODO(adonovan): eventually replace this function with the
	// simpler and more efficient (*go/token.File).LineStart, added
	// in go1.12.

	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
		}
	}
}