Convert a number into english words (Indian numbering system) in ruby

number_to_words.rb

# https://stackoverflow.com/a/43522719 + couple of fixes

def number_to_words(num)
  numbers_to_name = {
    10_000_000 => "crore",
    100_000 => "lakh",
    1000 => "thousand",
    100 => "hundred",
    90 => "ninety",
    80 => "eighty",
    70 => "seventy",
    60 => "sixty",
    50 => "fifty",
    40 => "forty",
    30 => "thirty",
    20 => "twenty",
    19 => "nineteen",
    18 => "eighteen",
    17 => "seventeen",
    16 => "sixteen",
    15 => "fifteen",
    14 => "fourteen",
    13 => "thirteen",
    12 => "twelve",
    11 => "eleven",
    10 => "ten",
    9 => "nine",
    8 => "eight",
    7 => "seven",
    6 => "six",
    5 => "five",
    4 => "four",
    3 => "three",
    2 => "two",
    1 => "one"
  }

  log_floors_to_ten_powers = {
    0 => 1,
    1 => 10,
    2 => 100,
    3 => 1000,
    4 => 1000,
    5 => 100_000,
    6 => 100_000,
    7 => 10_000_000
  }

  num = num.to_i
  return '' if (num <= 0) || (num >= 100_000_000)

  log_floor = Math.log(num, 10).round(15).floor
  ten_power = log_floors_to_ten_powers[log_floor]

  if num <= 20
    numbers_to_name[num]
  elsif log_floor == 1
    rem = num % 10
    [numbers_to_name[num - rem], number_to_words(rem)].join(' ')
  else
    [number_to_words(num / ten_power), numbers_to_name[ten_power], number_to_words(num % ten_power)].join(' ').strip
  end
end

Workaround for floating point error in Math.log output taken from here - https://stackoverflow.com/a/56370318/923080