* Bi-linear interpolation - round towards nearest integer
Add the equivalent of 0.5 to the final calculation pre-rounding.
This will have the effect of rounding to the nearest integer, rather
than truncating. I.e. rounding down
* Unit tests: isolate table tests and check interpolation x/y bins
* Unit tests: add native table3d tests
* Unit tests: derive min/max from axis test values
* Unit tests: more detailed messages
* Unit tests: fix rounding & unit tests
* Performance
* Performance: use uint16_t instead of unsigned long
for the fixed point math: we only need the fractional
part. I.e. 1.16 not 16.16
* Use narrowest possible type
* Optimise bin position logic for performance
* Only promote to uint32_t when really required.
* Simplify bin checks - no zero width bins
* Save memory: use a single byte for the last bin caches
* Performance: increment pointers instead of
repeatedly dereferncing array by index.
* Comments
* Incorrect array underrun logic
* Rename type, comments
* Fix unit tests
tx_haggis