Pre-compute and use contiguous wedge masks.

This is purely a refactoring patch and has no functional effect.

Uses of these masks can be arranged such that all input blocks are
contiguous in memory (stride == block width). In this case 1D versions
of  operations can be used. 1D vector operations have superior performance
over 2D block equivalents as they are more processor cache friendly and
they can do away with a second loop overhead.

Change-Id: I2b76c9888aea2c857cc497e8a4b2841fd3dad54e