View source for PKWARE DCL Implode

== Identification ==
A DCL Implode datastream starts with a two-byte header. The first byte indicates the type of compression:
* <code>0x00</code>: binary compression
* <code>0x01</code>: ASCII compression (a method optimized for compressing text)

The second byte specifies the size of the dictionary:
* <code>0x04</code>: 1024 bytes
* <code>0x05</code>: 2048 bytes
* <code>0x06</code>: 4096 bytes

Most common is {{magic|0x00 0x06}}, indicating binary compression and a 4K dictionary.

Since the header bytes aren't very discriminating, it may be worth noting that the ''last'' 3 bytes of the datastream will match one of these 8 bit-patterns (assuming padding bits are 0, and there are no padding bytes):

 ... xxxxxxxx 00000001 11111111
 ... 1xxxxxxx 10000000 01111111
 ... 01xxxxxx 11000000 00111111
 ... 001xxxxx 11100000 00011111
 ... 0001xxxx 11110000 00001111
 ... 00001xxx 11111000 00000111
 ... 000001xx 11111100 00000011
 ... 0000001x 11111110 00000001

Caution: In some uses of this compression, e.g. by [[TSComp|The Stirling Compressor]] or [[PC-Shrink]], zero-length input compresses to zero-length output. In this special case, neither the header nor the last few bytes are present.