Python and JS implementations

[DonaldTsang]

Python would be used for toying around and general scripting.
JS implementation woulb be used for web applications.

[DonaldTsang]

partial solution

x = ['!','$','%','(',')','*','+',',','-','.','0','1','2','3','4','5',
    '6','7','8','9',';','=','>','@','A','B','C','D','E','F','G','H',
    'I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X',
    'Y','Z','[',']','^','_','`','a','b','c','d','e','f','g','h','i',
    'j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y',
    'z','{','|','}','~']
    
b = b"\xFE\xE1\xDE\xAD"

def encode_chunk(byte):
  assert type(byte) == bytes and len(byte) == 4
  accum = sum([byte[i]<<(8*(3-i)) for i in range(4)])
  return "".join([x[(accum//(85**(4-i)))%85] for i in range(5)])

def decode_chunk(string):
  assert type(string) == str and len(string) == 5
  accum = sum([x.index(string[i])*(85**(4-i)) for i in range(5)])
  return b"".join([bytes([(accum>>(8*(3-i)))&255]) for i in range(4)])

def encode_byte(byte):
  assert type(byte) == bytes
  byte = [byte[i:i+4] for i in range(0, len(byte), 4)]
  return "".join([encode_chunk(i) for i in byte])

def decode_byte(string):
  assert type(string) == str
  string = [string[i:i+5] for i in range(0, len(string), 5)]
  return b"".join([decode_chunk(i) for i in string])

[kstenerud]

Yes, if you'd like to help out with implementations in other languages, I'll include them here :)

The C implementation was only intended as a lowest common denominator reference implementation, since all languages have C bindings.

[DonaldTsang]

Made a useful class for this

class conversion:
  char_set, byte_count, char_chunk, base = None, None, None, None

  def conversion(self,char_set,byte_count,char_chunk,base):
    self.char_set = char_set
    self.byte_count = byte_count
    self.char_chunk = char_chunk
    self.base = base

  def encode_chunk(self,byte):
    assert type(byte) == bytes and len(byte) == self.byte_count
    accum = sum([byte[i]<<(8*(self.byte_count-i-1)) for i in range(self.byte_count)])
    return "".join([x[(accum//(self.base**(self.char_chunk-i-1)))%self.base] for i in range(self.char_chunk)])

  def decode_chunk(self,string):
    assert type(string) == str and len(string) == self.char_chunk
    accum = sum([x.index(string[i])*(self.base**(self.char_chunk-i-1)) for i in range(self.char_chunk)])
    return b"".join([bytes([(accum>>(8*(self.byte_count-i-1)))&255]) for i in range(self.byte_count)])

  def encode_byte(self,byte):
    assert type(byte) == bytes
    byte = [byte[i:i+self.byte_count] for i in range(0, len(byte), self.byte_count)]
    return "".join([self.encode_chunk(i) for i in byte])

  def decode_byte(self,string):
    assert type(string) == str
    string = [string[i:i+self.char_chunk] for i in range(0, len(string), self.char_chunk)]
    return b"".join([self.decode_chunk(i) for i in string])