It was chosen to avoid a number of the most annoying ambiguous letter shapes for hand-entry of long address strings.
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.
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.
Now you've got me curious on the performance of base58 to base64 hah. Down the rabbit hole i go. Appreciate your reply, thanks :)
I didn’t look into it much but it seems like a great encoding even outside of this project. Predictable length, reasonable density, “double clickable” etc. I’ve been annoyed with both hex and base64 for a while so it’s pretty cool just by itself.
> Re: prefix, is the concern that I haven't defined the allowed character set as part of the spec?
Yeah, the worry is almost entirely “subtle deviations across stacks”, which is usually due to ambiguous specs. It’s so annoying when there’s minor differences, compatibility options etc (like base64 which has another “URL-friendly” encoding - ugh).