implement base64 decoding

go/encode.go

@@ -39,8 +39,50 @@ func base64encode(b []byte) []byte {
	return res
}
func decode(b byte) byte {
	if 'A' <= b && b <= 'Z' {
		return b - 'A'
	} else if 'a' <= b && b <= 'z' {
		return 26 + b - 'a'
	} else if '0' <= b && b <= '9' {
		return 52 + b - '0'
	} else if b == '+' {
		return 62
	} else if b == '/' {
		return 63
	} else {
		fmt.Println("oops")
		return ' '
	}
}
func base64decode(b []byte) []byte {
	res := make([]byte, len(b) / 4 * 3)
	//fmt.Println(len(b), "->", len(res))
	for i := 0; i < len(b); i += 4 {
		c1, c2, c3, c4 := decode(b[i]), decode(b[i+1]), decode(b[i+2]), decode(b[i+3])
		r1 := (c1 << 2) + (c2 >> 4)
		r2 := ((c2 ^ ((c2 >> 4) << 4)) << 4) + (c3 >> 2)
		r3 := ((c3 ^ ((c3 >> 2) << 2)) << 6) + c4
		base := i - i / 4
		//fmt.Print(i, base, c1, c2, c3, c4, "\t", string(b[i]), string(b[i+1]), string(b[i+2]), string(b[i+3]))
		//fmt.Printf("\t -> '%s' '%s' '%s'\n", string(r1), string(r2), string(r3))
		res[base + 0] = r1
		res[base + 1] = r2
		res[base + 2] = r3
	}
	return res
}
func main() {
	base64 := base64encode([]byte("Hello, World!  "))
	//                                          ^^     (padded to a multiple of three)
	fmt.Println(string(base64))
	plain := base64decode(base64)
	fmt.Println(string(plain))
	secret := []byte("SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t")
	fmt.Println(string(secret))
	decoded := base64decode(secret)
	fmt.Println(string(decoded))
}