Huff0 : Early detection offers better speed (v0.7)

 In my earlier release, i skipped the integration of a simple to understand but more difficult to execute feature : early detection of border-cases segments.

This definition regroups both "not compressible segments" and "single character segments". The previous algorithm was correctly detecting these cases, but during the construction of the Huffman tree.

The new algorithm ensures these situations are detected before any operation is done to build the tree. It does so by counting differently, in a new structure created for this purpose. The net result is a speed improvement for files which feature such situations :

Detailed performance assessment :

		Huff0 v0.6			Huff0 v0.7
	Ratio	Compress	Decoding	Ratio	Compress	Decoding
Not compressible
enwik8.7z	1.000	810 MB/s	1.93 GB/s	1.000	870 MB/s	1.93 GB/s
Hardly compressible
win98-lz4hc-lit	1.024	465 MB/s	600 MB/s	1.024	485 MB/s	600 MB/s
audio1	1.070	285 MB/s	280 MB/s	1.070	285 MB/s	280 MB/s
Distributed
enwik8-lz4hc-lit	1.290	204 MB/s	194 MB/s	1.290	204 MB/s	194 MB/s
Lightly Ordered
enwik8-lz4hc-offh	1.131	197 MB/s	184 MB/s	1.131	197 MB/s	184 MB/s
Ordered
enwik8-lz4hc-ml	2.309	214 MB/s	195 MB/s	2.309	214 MB/s	195 MB/s
Squeezed
office-lz4hc-run	3.152	218 MB/s	202 MB/s	3.152	218 MB/s	202 MB/s
enwik8-lz4hc-run	4.959	245 MB/s	224 MB/s	4.959	245 MB/s	224 MB/s
Ultra compressible
loong	275	785 MB/s	2.93 GB/s	275	860 MB/s	2.93 GB/s

This (mostly) closes the gap with Range0 regarding the detection speed of not compressible segments, which is the main case to consider for real-life situations.

You can download and test the new version here :
http://fastcompression.blogspot.com/p/huff0-range0-entropy-coders.html