run-wc.txt

$ time wc test.txt
 16500000 49252094 2059004431 test.txt

real	0m5.930s
user	0m5.491s
sys	0m0.374s

$ go build wc.go && time ./wc test.txt
16500000 49252094 2059004431

real	0m2.947s
user	0m2.620s
sys	0m0.299s

wc.go

package main

import (
	"flag"
	"fmt"
	"io"
	"os"
)

func main() {
	if err := run(); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
}

func run() error {
	flag.Parse()
	f, err := os.Open(flag.Arg(0))
	if err != nil {
		return err
	}
	defer f.Close()

	var (
		ls       int
		ws       int
		bs       int
		wasSpace bool
	)

	buf := make([]byte, 16*4096)
	for {
		n, err := f.Read(buf)
		if err == io.EOF {
			break
		} else if err != nil {
			return err
		}
		bs += n

		for i := 0; i < n; i++ {
			switch buf[i] {
			case '\n':
				ls++
				fallthrough
			case ' ':
				if !wasSpace {
					ws++
					wasSpace = true
				}
			default:
					wasSpace = false
			}
		}
	}
	if !wasSpace {
		ws++
	}
	fmt.Printf("%d %d %d\n", ls, ws, bs)
	return nil
}