javascript v8 double base36 decode/encode in python

b36dec.py

# this is specific to the v8 js engine
# firefox actually does something slightly different so their encodings are incompatible

import sys
import math
import string
from functools import reduce
import numpy as np
from numpy import float64 as f64

alpha = string.digits + string.ascii_lowercase


# example input: ruse0iihfcd
# example output: 0.7737566290658499
def b36_double(b36):
    return reduce(lambda a, x: f64(alpha.index(x) + a) / 36, reversed(b36), 0)


# sadly python doesnt have an `unfold` so this looks a bit messy
def double_b36(d):
    d = f64(d)
    delta = f64(0.5) * (np.nextafter(d, 1) - d)
    # if d is a smoll boi
    delta = max(np.nextafter(f64(0), 1), delta)
    res = ''
    while d >= delta:
        d *= 36
        delta *= 36
        x = math.floor(d)
        d -= x
        res += alpha[x]
    return res


#print(double_b36(0.123456789))
print(b36_double(sys.argv[1]))