This class contains a pool of objects that can be used and reused
while minimizing the amount of required memory allocation and
deallocation operations

Includes:
- Replace SIGN macro with sgn2 function
- Avoid duplication of sgn function definition

CHECK statements added where invalid reference was detected.
Some variable names fixed.

- Enumerate filter types
- Define 6-tap vertical affine filter to reduce number of operations

Avoids dynamic memory allocation