68 lines
2.6 KiB
Markdown
68 lines
2.6 KiB
Markdown
# base-x
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[](https://www.npmjs.org/package/base-x)
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[](https://travis-ci.org/cryptocoinjs/base-x)
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[](https://github.com/feross/standard)
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Fast base encoding / decoding of any given alphabet using bitcoin style leading
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zero compression.
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**WARNING:** This module is **NOT RFC3548** compliant, it cannot be used for base16 (hex), base32, or base64 encoding in a standards compliant manner.
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## Example
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Base58
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``` javascript
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var BASE58 = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
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var bs58 = require('base-x')(BASE58)
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var decoded = bs58.decode('5Kd3NBUAdUnhyzenEwVLy9pBKxSwXvE9FMPyR4UKZvpe6E3AgLr')
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console.log(decoded)
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// => <Buffer 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>
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console.log(bs58.encode(decoded))
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// => 5Kd3NBUAdUnhyzenEwVLy9pBKxSwXvE9FMPyR4UKZvpe6E3AgLr
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```
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### Alphabets
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See below for a list of commonly recognized alphabets, and their respective base.
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Base | Alphabet
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------------- | -------------
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2 | `01`
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8 | `01234567`
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11 | `0123456789a`
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16 | `0123456789abcdef`
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32 | `0123456789ABCDEFGHJKMNPQRSTVWXYZ`
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32 | `ybndrfg8ejkmcpqxot1uwisza345h769` (z-base-32)
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36 | `0123456789abcdefghijklmnopqrstuvwxyz`
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58 | `123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz`
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62 | `0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ`
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64 | `ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/`
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67 | `ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_.!~`
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## How it works
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It encodes octet arrays by doing long divisions on all significant digits in the
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array, creating a representation of that number in the new base. Then for every
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leading zero in the input (not significant as a number) it will encode as a
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single leader character. This is the first in the alphabet and will decode as 8
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bits. The other characters depend upon the base. For example, a base58 alphabet
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packs roughly 5.858 bits per character.
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This means the encoded string 000f (using a base16, 0-f alphabet) will actually decode
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to 4 bytes unlike a canonical hex encoding which uniformly packs 4 bits into each
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character.
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While unusual, this does mean that no padding is required and it works for bases
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like 43.
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## LICENSE [MIT](LICENSE)
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A direct derivation of the base58 implementation from [`bitcoin/bitcoin`](https://github.com/bitcoin/bitcoin/blob/f1e2f2a85962c1664e4e55471061af0eaa798d40/src/base58.cpp), generalized for variable length alphabets.
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