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From: tony@deepthought.Sgi.COM (Tony Leavitt)
Newsgroups: comp.lang.ada
Subject: Run-time checking and speed
Date: 10 Jan 1995 22:20:14 GMT
Organization: Silicon Graphics, Inc.
Sender: tony@deepthought (Tony Leavitt)
Distribution: world
Message-ID: <3ev16u$ojc@pong.lasc.lockheed.com>
NNTP-Posting-Host: deepthought.lasc.lockheed.com
Date: 1995-01-10T22:20:14+00:00
List-Id: <comp.lang.ada>

I have a question about developing Ada code that still has all of
its normal run-time checking and is "fast."  Is there an execution
difference with repsect to run-time checking in any of the following.
Or, is there "a good real-time style" for this type of stuff? 



-- CASE 1
-- This case seems to need all of the full run-time checking since
-- the variables x and y can be unlimited when accessing the array.

XY_array : array (integer range 1..100, integer range 1..100) of float ;

for x in 1..100 loop
  for y in 1..100 loop
     XY_array(x,y) := calc_something  ;
   end loop ;
end loop ;



-- CASE 2
-- This case it seems that no runtime checking is needed when
-- accessing the array since x and y are, by definition, within
-- the array bounds (assuming memory doesn't go bad while running).

subtype arraybounds is integer range 1..100 ;

XY_array : array (arraybounds, arraybounds) of float ;

for x in arraybounds loop
  for y in arraybounds loop
     XY_array(x,y) := calc_something  ;
   end loop ;
end loop ;



-- CASE 3
-- This seems similar to CASE 2

XY_array : array (integer range 1..100, integer range 1..100) of float ;

for x in XY_array'Range(1) loop
  for y in XY_array'Range(2) loop
     XY_array(x,y) := calc_something  ;
   end loop ;
end loop ;




I've used loops since they are simple, but other issues are the same.
For example, I could have a function compute the array indices and return
either integers or arraybounds.  If I return arraybounds, it seems that
the run-time check would occur at assigning the arraybounds and not when
accessing the array.

TIA,

-- 

Tony Leavitt

Email: tony@gelac.lasc.lockheed.com