Rationale for Ada 2012

John Barnes
Contents   Index   References   Search   Previous   Next 

9.4.2 Cyclic fixed point

Measurements in the physical world of Euclid and Newton are either lengths or angles. Angles are cyclic in nature and so can be mapped with a modular type. However, this leaves scaling in the hands of the user and is machine dependent. Consideration was given to the possibility of a cyclic form of fixed point. Sadly, there was much hidden complexity and so no solution was agreed. (See AI-175).
One might have thought that it would be easy to use the natural wrap-around hardware. However, with a binary machine, if 180 degrees is held exactly then 60 degrees is not which excludes an exact representation of an equilateral triangle. The whole point about using fixed point is that it is precise but it just doesn't work unless the hardware uses a base with divisibility by 60. The Babylonians would have understood. The text of AI-175 includes a generic which might be useful for many applications.

Contents   Index   References   Search   Previous   Next 
© 2011, 2012, 2013 John Barnes Informatics.
Sponsored in part by:
The Ada Resource Association:


and   Ada-Europe: