From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: f891f,eac70c5fad02d925,start
X-Google-Attributes: gidf891f,public
X-Google-Thread: 103376,eac70c5fad02d925,start
X-Google-Attributes: gid103376,public
From: ok@goanna.cs.rmit.EDU.AU (Richard A. O'Keefe)
Subject: Concerning subscript bounds checks
Date: 1996/06/21
Message-ID: <4qdj3e$btf@goanna.cs.rmit.EDU.AU>#1/1
X-Deja-AN: 161344676
summary: Good one, Ada!
organization: Comp Sci, RMIT, Melbourne, Australia
keywords: subscripts
newsgroups: comp.lang.ada,comp.lang.misc
nntp-posting-user: ok
Date: 1996-06-21T00:00:00+00:00
List-Id: <comp.lang.ada>


There was some discussion in comp.lang.misc recently about array bounds
checks.  As an exercise, I converted Algorithm AS 47 (an implementation
of the Nelder-Mead simplex minimisation procedure) from Fortran to Ada.

The Fortran original contains 85 array subscripts.
The Ada version      contains 66 array subscripts.
Of these 66, all but 4 occur within the scope of a "for" loop
which *obviously* guarantees the safety of the subscript.

The remaining 4 occur in this context:
    subtype Simplex_Range is Natural range 0 .. Point'Length;
    P: "array (Simplex_Range) of ..."
    Y: "array (Simplex_Range) of ..."
    X: Point;
    J: Simplex_Range;
    ...
    J := 0;		-- at the start, J = Simplex_Range'First
    for I in X'Range loop
	...
	P(J) := ...
	Y(J) := ...
	J := J + 1;
    end loop;		-- at the end, J = Simplex_Range'Last
    P(J) := ...
    Y(J) := ...
end;

A reasonably smart compiler should be able to tell that these four
subscripts are also safe.

-- 
Fifty years of programming language research, and we end up with C++ ???
Richard A. O'Keefe; http://www.cs.rmit.edu.au/~ok; RMIT Comp.Sci.