go tour rot13 exercise I imagine the strings.ToLower version is much slower. experimenting is all.

rot13.go

package main

import (
	"io"
	"os"
	"strings"
)

type rot13Reader struct {
	r io.Reader
}

func (rot *rot13Reader) Read(p []byte) (n int, err error) {
	n, err = rot.r.Read(p)

	for i := 0; i < len(p); i++ {
		lc := strings.ToLower(string(p[i]))
		if lc >= "a" && lc <= "m" {
			p[i] += 13
		} else if lc >= "n" && lc <= "z" {
			p[i] -= 13
		}
//		if p[i] >= 'A' && p[i] <= 'M' || p[i] >= 'a' && p[i] <= 'm' {
//			p[i] += 13
//		} else if p[i] >= 'N' && p[i] <= 'Z' || p[i] >= 'n' && p[i] <= 'z' {
//			p[i] -= 13
//		}
	}

	return
}

func main() {
	s := strings.NewReader(
	"Lbh penpxrq gur pbqr!")
	r := rot13Reader{s}
	io.Copy(os.Stdout, &r)
}