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base-x-bytearray

Fast base encoding / decoding of any given alphabet to Uint8Array/Buffer

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base-x

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js-standard-style

Fast base encoding / decoding of any given alphabet using bitcoin style leading zero compression.

This is forked from cryptocoinjs/base-x

And simply uses Uint8array if Buffer isn't already available.

Example

Base58

var BASE58 = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
var bs58 = require('base-x')(BASE58)

var decoded = bs58.decode('5Kd3NBUAdUnhyzenEwVLy9pBKxSwXvE9FMPyR4UKZvpe6E3AgLr')

console.log(decoded)
// => <Uint8array- 80 ed db dc 11 68 f1 da ea db d3 e4 4c 1e 3f 8f 5a 28 4c 20 29 f7 8a d2 6a f9 85 83 a4 99 de 5b 19>

console.log(bs58.encode(decoded))
// => 5Kd3NBUAdUnhyzenEwVLy9pBKxSwXvE9FMPyR4UKZvpe6E3AgLr

Alphabets

See below for a list of commonly recognized alphabets, and their respective base.

BaseAlphabet
201
801234567
110123456789a
160123456789abcdef
320123456789ABCDEFGHJKMNPQRSTVWXYZ
360123456789abcdefghijklmnopqrstuvwxyz
58123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz
620123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
64ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/
66ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_.!~

How it works

It encodes octet arrays by doing long divisions on all significant digits in the array, creating a representation of that number in the new base. Then for every leading zero in the input (not significant as a number) it will encode as a single leader character. This is the first in the alphabet and will decode as 8 bits. The other characters depend upon the base. For example, a base58 alphabet packs roughly 5.858 bits per character.

This means the encoded string 000f (using a 0-f alphabet) will actually decode to 4 bytes unlike a typical hex codec which uniformly packs 4 bits into each character.

While unusual, this does mean that no padding is required and it works for bases like 43. If you need standard hex encoding or base64 encoding you probably don't want this.

The algorithm used to convert the base of the number is roughly this:

significant =  12345
base = 16
digits = []
while significant > base:
  significant, remainder = divmod(significant, base)
  digits.append(remainder)
digits.append(significant)
assert list(reversed(digits)) == [3,0,3,9]
assert hex(12345) == '0x3039'

Of course the input is actually an array of digits already :)

License

This library is free and open-source software released under the MIT license.

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Package last updated on 31 Mar 2017

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