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Re: Base64 encoding

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jonas.thornvall@gmail.com writes:

> Den lördag 14 mars 2015 kl. 12:20:43 UTC+1 skrev jonas.t...@gmail.com:
>> Den lördag 14 mars 2015 kl. 12:12:14 UTC+1 skrev jonas.t...@gmail.com:
>> > Den lördag 14 mars 2015 kl. 11:56:15 UTC+1 skrev Ben Bacarisse:
>> > > jonas.thornvall@gmail.com writes:
<snip>
>> > > > Could the below logic represent how a conversion could be done.
<snip>
>> > > > 1. Get the byte values with charCodeAt
>> > > > 2. Treat the bytevalues from string as base 256.
>> > > > 3. Convert the base 256 value to base 10. (do not know howto go from
>> > > > 256 to 64 right out of head)
>> > > > 4. Convert base 10 into base 64.
>> > > > 5. Map the characters upon the base 64 encoded.
>> > > >
>> > > > Maybe it is wrong?
>> > > 
>> > > The main error is that the values from charCodeAt are not eight bits
>> > > wide but up to 16 bits wide, but you also need to take care of the
>> > > padding issue -- the number of encoded bytes may not be a multiple of
>> > > three.  Obviously the issue is slightly different when encoding 16-bit
>> > > values.
<snip>
>> > But isn't the ascii table 8-bit?

Yes, but ECMAScript uses 16 bit numbers to represent characters in a
string.  You are free to limit yourself to only encoding those strings
that containing character values from 0 to 255, but there will be
strings with characters outside of this range.

<snip>
>> Maybe i missunderstand you are you saying that three ASCII character
>> encoded as 16-bit? Then it is just a subset of the ASCII character
>> set allowed?
>
> Are they encoded as triplets?

In a sense, yes.  Think about how the two strings "a" and "aa" would be
base-64 encoded.  The encoding is specified by an RFC:

  https://www.rfc-editor.org/info/rfc4648

so it's not hard to find all the details.

-- 
Ben.

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Base64 encoding jonas.thornvall@gmail.com - 2015-03-13 23:15 -0700
  Re: Base64 encoding Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-03-14 10:56 +0000
    Re: Base64 encoding jonas.thornvall@gmail.com - 2015-03-14 04:12 -0700
      Re: Base64 encoding jonas.thornvall@gmail.com - 2015-03-14 04:20 -0700
        Re: Base64 encoding jonas.thornvall@gmail.com - 2015-03-14 05:01 -0700
          Re: Base64 encoding Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-03-14 12:45 +0000
  Re: Base64 encoding Richard Damon <Richard@Damon-Family.org> - 2015-03-14 09:46 -0400

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