There are four basic source files for each compression layout:
1) hor_full.c: fully packed horizontal bit packing
2) hor_word.c: word aligned horizontal bit packing
3) ver_64.c:   vertical bit packing with k = 64
4) ver_8192.c: vertical bit packing with k = 8192
The raw.c is uncompressed scanning and the rand.c & rand.h
contain helper functions for random number generation.
The _SCALAR macro can be defined (-D_SCALAR) in files
hor_full.c hor_word.c and ver_64.c to show performance
using scalar code. Otherwise, the default is SIMD code.
