SitxBrimstoneAlgorithm

Introduction

Brimstone is based on PPMd variant G, with some changes.

Differences

• The first 128 states of MaxContext in the initialization are given the frequency 2. The last 128 are given the frequency 1 as in the original.
• All code related to the LastBreath variable in the suballocator is removed.
• The range coder uses 65536 as the "bottom" value, instead of 32768.

Data stream

The data stream begins with two bytes giving the PPMd settings. The first is the suballocator size, given as the two-logarithm of the number of bytes allocated. In other words, the size will be 2^byte1. Allowed values are between 16 and 30, inclusive. The second is the max order value. Allowed values are between 2 and 16, inclusive.

This is followed by the byte stream from the range coder.