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From: Phil Clayton <phil.clayton@lineone.net>
Newsgroups: comp.lang.ada
Subject: Re: Pascal Calling Convention
Date: Wed, 30 Mar 2011 06:42:39 -0700 (PDT)
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Date: 2011-03-30T06:42:39-07:00
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On Mar 29, 1:23 pm, stefan-lu...@see-the.signature wrote:
> The original C++ from Hyman Rosen was
>
> template <unsigned N>
> class set
> {
> =A0 =A0 unsigned n; =A0 =A0// number of members in set
> =A0 =A0 unsigned d[N]; // members are in d[0..n-1]
> =A0 =A0 unsigned s[N]; // d[s[k]] =3D=3D k if k is a member
> =A0 =A0 // unspecified elements of d and s are arbitrary
>
> public:
> =A0 =A0 set() : n(0) { }
> =A0 =A0 bool has(unsigned k)
> =A0 =A0 =A0 =A0 { return k < N && s[k] < n && d[s[k]] =3D=3D k; }
> =A0 =A0 void add(unsigned k)
> =A0 =A0 =A0 =A0 { if (k < N && !has(k)) { d[n] =3D k; s[k] =3D n++; }
> =A0 =A0 void del(unsigned k)
> =A0 =A0 =A0 =A0 { if (has(k)) { unsigned i =3D s[k]; d[i] =3D d[--n]; s[d=
[i]] =3D i; }
> =A0 =A0 void clr() { n =3D 0; }
>
> };

Interesting.  It's worth noting that if N is equal to the number of
keys representable by unsigned and every key is added to the set, n++
in the final add will 'overflow' because n (of type unsigned) needs to
be able to have the range 0 .. N, i.e. N + 1 distinct values.  I doubt
this would cause a problem in practice because
1. unsigned is likely to be at least 32 bits these days(?) so N will
be much smaller;
2. these are designed for sparse arrays, there is a low probability of
filling the entire array.

Clearly I'm not the first person to notice this though...

On Mar 29, 1:23 pm, stefan-lu...@see-the.signature wrote:
>    type Elements is mod <>;
>    ...
>    subtype Counter_Type is Integer range 0 .. Integer(Elements'Last)+1;

Phil