Why padding is used in Base64 encoding? [duplicate]

Question

Possible Duplicate:
Why does base64 encoding requires padding if the input length is not divisible by 3?

Quoting Wikipedia:

...these padding characters must then be discarded when decoding but still allow the calculation of the effective length of the unencoded text, when its input binary length would not be a multiple of 3 bytes. ...

But the calculation of length raw data can easily be done even if strip the padding character.

          |               Encoded
          |--------------------------------------
Raw Size  | Total Size | Real Size | Padding Size
1         | 4          | 2         | 2
2         | 4          | 3         | 1
3         | 4          | 4         | 0
4         | 8          | 6         | 2
5         | 8          | 7         | 1
6         | 8          | 8         | 0
7         | 12         | 10        | 2
8         | 12         | 11        | 1
9         | 12         | 12        | 0
10        | 16         | 14        | 2
.
.
.

So given the real encoded size (third column) you can always correctly guess what padded size would be:

PaddedSize = 4 * Ceil (RealSize / 4)

So in theory, there was no need of padding. Algorithm would have handled it. Considering that Base64 encoding is a popular industry standard, it is used in many applications and devices. These would have benefited from reduced encoded size. So question is, why padding is used in Base64 encoding?

Answer 1

It makes the encoded message an integer multiple of 4 characters. This might make writing a decoder slightly easier. You can load and process characters in blocks of 4 and convert them to 3 output characters, and the padding makes it easy to do this without going off the end of the string.

Answer 2

As you note, the end-padding is at most 2 bytes in length regardless of the length of the message, so it's not a really significant saving - more of a micro-optimization. If your application is both the producer and consumer of the encoding, you could strip out the padding, but it's not really worth the hassle.