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@jsundram

jsundram/base64.py

Created March 30, 2016 01:32
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base64 encoding for integers. To make long numbers (i.e. hashes) more readable. Not as cool as RFC 1751, but less code.
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base64.py
ALPHABET = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_'
TABLE = {c: i for (i, c) in enumerate(ALPHABET)}
def decode(s, b=64):
"""Interpret the input string as a base b number"""
i, multiplier = 0, 1
for c in reversed(s):
i += multiplier * TABLE[c]
multiplier *= b
return i
def encode(h, b=64):
"""Given an hex string, convert to a base b number."""
assert b <= len(ALPHABET)
i = int(h, 16) # hex -> decimal
s = ''
while 0 < i:
i, d = divmod(i, b)
s += ALPHABET[d]
return s[::-1]
@dlamblin
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dlamblin commented Dec 13, 2018 •
edited
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Why not use the standard order and just change the +/ to -_?

ALPHABET='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'  #or
ALPHABET='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_'

I recommend (since b is a parameter) that the ALPHABET and TABLE actually be indexed by b like:

ALPHABET={
    56: '23456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnpqrstuvwxyz',
    58: '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz',
    64: 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/',
    '64u': 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_',
}
TABLE={b:{c: i for (i,c) in enumerate(ALPHABET[b])} for b in ALPHABET}

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