Re: Question for the folks who designed Ada95

[Marin David Condic <condicma@bogon.pwfl.com>]

Fraser Wilson wrote:
> 
> Here's a question: has anyone ever used a modular type which was not
> a power of 2, and lived to tell the tale?  What was the context?
> 
Reasonably often. I've found them useful as cycle counters or in
creating some form of circular queue. Certainly not as frequently as one
would, say, use the standard Integer, but often enough that I find it a
convenience.

I've seen a number of times in code something equivalent to:

X := X + 1 ;
if (X > Some_Max_Limit) then
    X := 0 ;
end if ;

A modular type of a non-power-of-2 makes this a natural thing because it
is the compiler's problem to figure out if we've hit the wraparound
point & it will likely do this as efficiently as possible.

I think I've seen this most frequently in some form of bus communication
where raw data is being buffered, buffers are being toggled or where
data is being read and dropping stale data is "a good thing". But I also
see it in code that deals with cyclic events - not all of which happen
in powers of two and quite frequently you want the ability to "tune" the
number of cycles by recompiling with new constants.

MDC
-- 
Marin David Condic
Real Time & Embedded Systems, Propulsion Systems Analysis
United Technologies, Pratt & Whitney, Large Military Engines
M/S 731-95, P.O.B. 109600, West Palm Beach, FL, 33410-9600
***To reply, remove "bogon" from the domain name.***

Visit my web page at: http://www.flipag.net/mcondic