Yappy levels mapping

[tansy]

Yappy levels mapping

I happen to check yappy and to my surprise it uses 100 levels. 100 levels that are virtually indistinguishable from each other.
Checked the source and I get where it come from but these levels are needlessly numerous.
While in the beginning they do provide measurable difference, later they are basically the same - difference in ratio between level 98 and 99 is 0.000434%.

# lzbench -eyappy silesia.tar

Compressor name  lv Compr.size Ratio  Filename 
yappy 2014-03-22 -0  109432876 51.63  silesia.tar
yappy 2014-03-22 -1  105755106 49.89  silesia.tar
yappy 2014-03-22 -2  103971220 49.05  silesia.tar
yappy 2014-03-22 -3  102945870 48.57  silesia.tar
yappy 2014-03-22 -4  102351839 48.29  silesia.tar
yappy 2014-03-22 -5  101910770 48.08  silesia.tar
yappy 2014-03-22 -6  101582066 47.93  silesia.tar
yappy 2014-03-22 -7  101303954 47.79  silesia.tar
yappy 2014-03-22 -8  100703725 47.51  silesia.tar
yappy 2014-03-22 -9  100158415 47.25  silesia.tar
yappy 2014-03-22 -10 100020279 47.19  silesia.tar
(...)     
yappy 2014-03-22 -95  98683510 46.56  silesia.tar
yappy 2014-03-22 -96  98682010 46.56  silesia.tar
yappy 2014-03-22 -97  98675172 46.55  silesia.tar
yappy 2014-03-22 -98  98674715 46.55  silesia.tar
yappy 2014-03-22 -99  98673795 46.55  silesia.tar

So I tried what every gzip dev would do - map these levels into smaller, more meaningful and manageable range, namely 1..9.
As returns from more 'levels' diminishes quickly, likely at exponential pace so I decided to choose exponential number of iterations as a yardstick and comeup with this formula:

# "lzbench-yappy-9_lv__lv2=(1<<lv)>>2" -eyappy,1,2,3,4,5,6,7,8,9 silesia.tar

Compressor name  lv  old Compr.size Ratio  Filename 
yappy 2014-03-22 -1    0  109432876 51.63  silesia.tar
yappy 2014-03-22 -2    1  105755106 49.89  silesia.tar
yappy 2014-03-22 -3    2  103971220 49.05  silesia.tar
yappy 2014-03-22 -4    4  102351839 48.29  silesia.tar
yappy 2014-03-22 -5    8  100703725 47.51  silesia.tar
yappy 2014-03-22 -6   16   99471363 46.93  silesia.tar
yappy 2014-03-22 -7   32   98912604 46.67  silesia.tar
yappy 2014-03-22 -8   64   98734033 46.58  silesia.tar
yappy 2014-03-22 -9  128   98644248 46.54  silesia.tar

Now differece in ratio between levels 8 and 9 is 0.042359%. Still very little, but somewhat more meaningful. 100 times more.
The low levels are also well 'spread', correspondingly with their performance.