What's the deal with Base64?

[greenmachine]

I got the idea to make an all-around base converter to change numbers from one base to another. I'm about 99% done - or at least I thought I was until I went and looked up Base64 notation to make sure I was using the right characters. Up until I looked it up, I had assumed that it would follow the same pattern as the lower bases: 0-9 for the numbers 0-9, then A-F (in hex) for 10-15. I assumed this would keep going, so that base 36 would have 0-9 and then A-Z (10-36), and base 62 would have 0-9, A-Z, and a-z. Base64 introduces '+' and '/' for the values 62 and 63, but then also places A-Z first, followed by a-z and then 0-9 (+ and / are last either way).

Why all of a sudden do the places switch? Is there a reason that A-Z is before the numbers, even though it makes more sense the other way? Or is Base64 really different, and I am just too unfamiliar with it to know?

Base64 also has = as a "pad" character, which I don't understand either....

[flyingboz]

I got the idea to make an all-around base converter to change numbers from one base to another. Base64 also has = as a "pad" character, which I don't understand either....

Base64 is an encoding/decoding mechanism designed to move big ascii through smtp servers that weren't built for it - mail was an english text only affair back in the day

The algorithms you will find googling for base64 implementations likely will have little to do with number base arithmetic. They simply provide a standardized way of taking things bigger than ascii 127 and representing them in a manner that an original SMTP server could process without munging. That's where

the Line length and padding come into play.

If you are purely interested in the math, implement in the same way you would binary, decimal or hex.