[aftbit]

My personal favorite encoding is base58 aka Bitcoin address encoding. It uses characters [A-Za-z0-9] except for [0OIl]. It is almost as dense as base64, "double clickable", but not (as) predictable in length as base32.

It was chosen to avoid a number of the most annoying ambiguous letter shapes for hand-entry of long address strings.

https://en.bitcoin.it/wiki/Base58Check_encoding

[bredren]

Reminds me that Windows activation keys used to exclude a broader set of characters to avoid transcription errors: looking it up again: 0OI1 and 5AELNSUZ

[unshavedyak]

Is there a good reason why Base63 (nopad) doesn't exist? Ie Base64 minus the `-`, so that you almost get the density of base64 (nopad) but the double click friendly feature.

I was reviewing encodings recently and didn't want to drop all the way down to base32, but for some reason the library i was using didn't allow anything beyond base32 and bas64 variants, despite having a feature where you can define your own base.

I thought maybe it was performance oriented. An odd prefix length like base63 would mean .. i think, a slightly more computationally demanding set of encoding instructions?

Either way i basically want base58 but i don't care about legibility, i just wanted double click and url friendly characters.

[fauigerzigerk]

>Is there a good reason why Base63 (nopad) doesn't exist? Ie Base64 minus the `-`, so that you almost get the density of base64 (nopad) but the double click friendly feature.

Yes, the reason is that you need 64 characters if you want each character to encode 6 bits as log2(64) == 6. If you only have 63 characters in your alphabet then one of your 6-bit combinations has no character to represent it.

Base32 can represent 5 bits per character because log2(32) == 5. Anything in between 32 and 64 doesn't buy you anything because there is no integer between 5 and 6.

[unshavedyak]

Is that "just" a performance concern though? Ie why is there a base58 and base62 but no base63?

Now you've got me curious on the performance of base58 to base64 hah. Down the rabbit hole i go. Appreciate your reply, thanks :)

[TedDoesntTalk]

It’s not too difficult to write your own encoding. Probably 10 lines of code or less if you hard-code your encoding alphabet.