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: runewidth_posix.go
    path of file: ./repos/podman/vendor/github.com/mattn/go-runewidth
    
    the code of the file until where you have to start completion: //go:build !windows && !js && !appengine
// +build !windows,!js,!appengine

package runewidth

import (
	"os"
	"regexp"
	"strings"
)

var reLoc = regexp.MustCompile(`^[a-z][a-z][a-z]?(?:_[A-Z][A-Z])?\.(.+)`)

var mblenTable = map[string]int
    
func IsEastAsian() bool {
	locale := os.Getenv("LC_ALL")
	if locale == "" {
		locale = os.Getenv("LC_CTYPE")
	}
	if locale == "" {
		locale = os.Getenv("LANG")
	}

	// ignore C locale
	if locale == "POSIX" || locale == "C" {
		return false
	}
	if len(locale) > 1 && locale[0] == 'C' && (locale[1] == '.' || locale[1] == '-') {
		return false
	}

	return isEastAsian(locale)
}