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: stack_tags.go
    path of file: ./repos/goldfish/vendor/github.com/jtolds/gls
    
    the code of the file until where you have to start completion: package gls

// so, basically, we're going to encode integer tags in base-16 on the stack

const (
	bitWidth       = 4
	stackBatchSize = 16
)

var (
	pc_lookup   = make(map[uintptr]int8, 17)
	mark_lookup [16]func(uint, func())
)

func init() {

    
func readStackTag() (tag uint, ok bool) {
	var current_tag uint
	offset := 0
	for {
		batch, next_offset := getStack(offset, stackBatchSize)
		for _, pc := range batch {
			val, ok := pc_lookup[pc]
			if !ok {
				continue
			}
			if val < 0 {
				return current_tag, true
			}
			current_tag <<= bitWidth
			current_tag += uint(val)
		}
		if next_offset == 0 {
			break
		}
		offset = next_offset
	}
	return 0, false
}