GVRS C API testing on Raspberry PI

[gwlucastrig]

This morning, I began testing the GVRS C API on a Raspberry Pi 5 running under Linux.

The source code built and ran the first time, with no suprises. The test files for GVRS were stored on the Micro SD
card file system. In the tests results shown below, the most meaningful values are probably the "Row Major" performance
test which shows about 40 million lookup operations per second for the uncompressed version (ETOPO1_v4.gvrs) and
about 14.8 lookup operations per second for the compressed version (ETOPO1_v4_comp.gvrs).

Read Performance for file /home/gwlucas/GridfourC/data/ETOPO1_v4.gvrs
Test                     Time (sec)    Operations    Operations/sec
Tile Access                0.086            10800      125581.4
Tile Block Access          5.685        233280000    41034300.8
Row Major Order            5.821        233280000    40075588.4
Column Major Order         6.145        233280000    37962571.2
    
Read Performance for file /home/gwlucas/GridfourC/data/ETOPO1_v4_comp.gvrs
Test                     Time (sec)    Operations    Operations/sec
Tile Access               10.017            10800        1078.2
Tile Block Access         15.580        233280000    14973042.4
Row Major Order           15.673        233280000    14884195.8
Column Major Order        16.018        233280000    14563615.9

Raspberry Pi is a new environment for me, so I welcome any suggestions about testing and development that you may have.

[gwlucastrig]

I've been lucky enough to find some substantial opportunities for speeding up the reading of GVRS data, particularly for the canonical Huffman variation.

Read time for the file cited above is now about 3.5 seconds for the "Tile Access" test. The Tile Access test measures the time required to read data from a file and decompress it, but does not account for the overhead of marshalling each individual data value for presentation to the calling application (there are 233 million data value to be transferred, so it adds up).

For a variation of the ETOPO1 file that used data compression based on the canonical Huffman format exclusively, the time to access the file averaged 2.145 seconds across multiple tests.