[patch] HPEC CFAR Detection benchmark

[Don McCoy]

The attached patch implements the CFAR benchmark.  Briefly, this problem 
involves finding targets based on data within a three-dimensional cube 
of 'beam locations', 'range gates' and 'doppler bins'.  It does this by 
comparing the signal in a given cell to that of nearby cells in order to 
avoid false-detection of targets.  The range gate parameter is varied 
when considering 'nearby' cells.  A certain number of guard cells are 
skipped, resulting in a computation that sums the values from two thick 
slices of this data cube (one on either side of the slice for a 
particular range gate).  The HPEC PCA Kernel-Level benchmark paper has a 
diagram that shows one cell under consideration.  Please refer to it if 
needed.

The algorithm involves these basic steps:
   - compute the squares of all the values in the data cube
   - for each range gate:
     - sum the squares of desired values around the current range gate
     - compute the normalized power for each cell in the slice
     - search for values that exceed a certain threshold

Some of the code relates to boundary conditions (near either end of the 
'range gates' parameter), but otherwise it follows the above description.

For now, the original implementation used get/put (actually operator()) 
instead of using subviews and the element-wise operators.  Switching 
from one to the other resulted in about a 25% improvement in performance 
for the first set of data (see attached graph).  The other sets 
experienced improvement as well, to varying degrees.  I'd like to 
consider how we can improve the throughput further.  Switching the 
processing order may help possibly.  Thoughts are welcome.

The benchmark only varies the number of range gates based upon the four 
sets of parameters defined in the HPEC paper.  As the workload is 
equally dependent on each of the three dimensions, sweeping the other 
two would not add much value.

Regards,

-- 
Don McCoy
don (at) CodeSourcery
(888) 776-0262 / (650) 331-3385, .712

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