Module: Baseh::BaseN

Defined in:
lib/baseh/basen.rb

Overview

Fixed-length base-N encoding, spec section 5. Most significant digit first.

Class Method Summary collapse

Class Method Details

.alphabet_index(alphabet) ⇒ Object 



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# File 'lib/baseh/basen.rb', line 39

def alphabet_index(alphabet)
  alphabet.each_char.each_with_index.to_h
end

.decode_base_n(text, alphabet, index = nil) ⇒ Object

Spec 5.2. Raises INVALID_CHARACTER for symbols outside the alphabet.



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# File 'lib/baseh/basen.rb', line 22

def decode_base_n(text, alphabet, index = nil)
  index ||= alphabet_index(alphabet)
  base = alphabet.length
  value = 0
  text.each_char do |ch|
    digit = index[ch]
    if digit.nil?
      raise BasehError.new(
        "INVALID_CHARACTER",
        "Symbol #{ch.inspect} is not in the alphabet"
      )
    end
    value = value * base + digit
  end
  value
end

.encode_base_n(value, alphabet, length) ⇒ Object

Spec 5.1. All arithmetic stays in Integer (arbitrary precision).



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# File 'lib/baseh/basen.rb', line 9

def encode_base_n(value, alphabet, length)
  base = alphabet.length
  out = Array.new(length)
  v = value
  (length - 1).downto(0) do |pos|
    digit = v % base
    out[pos] = alphabet[digit]
    v /= base
  end
  out.join
end