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From: diamond@diamond.csl.sony.junet (Norman Diamond)
Newsgroups: comp.lang.pascal
Subject: Re: Realint qestion
Message-ID: <10254@socslgw.csl.sony.JUNET>
Date: 16 May 89 02:41:09 GMT
References: <19573@adm.BRL.MIL> <21930@santra.UUCP> <10247@socslgw.csl.sony.JUNET> <4664@freja.diku.dk>
Sender: news@csl.sony.JUNET
Reply-To: diamond@csl.sony.junet (Norman Diamond)
Organization: Sony Computer Science Laboratory Inc., Tokyo, Japan
Lines: 49

In article <21930@santra.UUCP> s32935k@taltta.hut.fi (Carl Torsten Stenholm) wrote:

>>>function realint (x: real): real;
>>>begin
>>>  realint := x - (x - trunc (x));
>>>end;

>>>Well now the only difference between this function and putting "trunc (x)" 
>>>directly in the code is that trunc returns an integer (I think).

I replied:

>>Suppose MAXINT is 2147whatever (about 2 billion), and x is -2.35e+3000 ?
In article <4664@freja.diku.dk> damm@freja.diku.dk (Kristian Damm Jensen) writes:

>In that case you would REALLY be in trouble since the code contains a
>call trunc (x).

Oh yeah, sorry.

>I that case you can't just use the standard trunc-function since the 
>restriction on types are much stronger on parameters than on plain assignment.
>In an assignment the types just has to be compatible (for the full 
>description of type compatibility see the Users Manual And Report 
>p. 159 (3. ed.))- in parameters they have BE the same type.

In fact, this is not correct.  Realint takes a *value* parameter, and
trunc effectively does the same.  For a *value* parameter, the actual
must be assignment-compatible to the formal, since it really is only
a kind of assignment.  Full compatibility is only required for *var*
parameters.  Please read the standard again, shortly before or after
the section you cited.

There is a minor difference, since trunc *returns* an integer.  The
integer can be converted back to real automatically, while the result
of realint cannot be converted back to integer automatically (it
would need a call to -- you guessed it -- trunc).  However, the user
of realint really wants a real from it, right?  So she could just call
trunc instead of realint.  He doesn't need realint.

In the C group a while back, there were discussions of SLMs (silly
little macros).  I guess realint might be this group's first SLF.
Doubtless there will be more SLFs and SLPs to follow.

--
Norman Diamond, Sony Computer Science Lab (diamond%csl.sony.co.jp@relay.cs.net)
  The above opinions are my own.   |  Why are programmers criticized for
  If they're also your opinions,   |  re-implementing the wheel, when car
  you're infringing my copyright.  |  manufacturers are praised for it?