Ascii85

Ascii85 is a form of ASCII Armor developed by Adobe Systems. It is more efficient at encoding binary data as ASCII characters than Base64, resulting in only a (approximately) 25% increase in data size versus 33% for base64.

It is mainly used by Adobe s PostScript and Portable Document Format file formats.

=Encoding and decoding method=

When encoding, the binary data is divided into groups of four bytes, which are treated as a 32-bit number, the first byte being the most significant (i.e., big-endian order). This number is then encoded as five numbers between 0 and 84 by repeatedly dividing it by 85. In fact, it is converted to radix 85. Again, the first number is the most significant. Five numbers is enough, because 855 is greater than 232. These numbers are then encoded as printable characters by adding 33 to them, giving the ASCII characters 33 ( ! ) to 117 ( u ).

Decoding uses the reverse procedure.

Further details: *Conventionally, the encoded data starts with are output, to further mark the end of the data. *Whitespace characters, like newlines, can be added at will. Other characters cause a decoding error. *Groups of characters that decode to a value greater then 232 − 1 will cause a decoding error, as will z characters in the middle of a group, and a final group consisting of only one character.

=Example=

The (historic) ,

: Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, that by a perseverance of delight in the continued and indefatigable generation of knowledge, exceeds the short vehemence of any carnal pleasure.

encoded in Ascii85 is as follows (remember to remove the End Of Line Terminators):