Path: utzoo!attcan!uunet!husc6!mailrus!ames!lll-lcc!pyramid!infmx!aland
From: aland@infmx.UUCP (Dr. Scump)
Newsgroups: comp.databases
Subject: Re: Informix 4gl - no integer arithmetic???
Summary: consistent with the documentation
Message-ID: <410@infmx.UUCP>
Date: 7 Sep 88 01:43:27 GMT
References: <466@pan.UUCP>
Organization: Informix Software Inc., Menlo Park, CA.
Lines: 55

In article <466@pan.UUCP>, jw@pan.UUCP (Jamie Watson) writes:
> 
> I have just discovered, the hard way, that in Informix 4gl the following
> statement, which contains only integer values, yields a most surprising
> result:
> 
> main
>   define
>     i integer
>   let i = 630 / 100 * 60
>   display i
> end main
> 
> Running this program produces a result of 378!!!
> 
> The 4gl manual states that all arithmetic is done in type 'decimal', which
> might explain what is going on here, but then it goes on to explain that
> for integer values, the specific type used is 'decimal(10,0)', which would

Um, that's for the *operands*, not necessarily the *result*.  See below...

> imply that the integer nature of the operations should be preserved.  It
> jw

This is consistent with the documentation.  

The type used for the integer *operands* is (10,0); since none of the
operands had scale, no precision is lost.  The scale of the operands
is *not necessarily* the scale used by the result (see page 1-13R of
the manual, second note).  The scale used in the *result* of an equation
depends on the equation; in this case, maximum scale is *22*, not 0,
due to the use of division (scale is 32 - 10 + 0 - 0, using the formula
on page 1-14R of the manual).  Therefore, the result of the right side
of the equation is 378.00000000..., which converts to integer +378 when
converting the value to integer at the end.

This is similar to C's promotion of types.  For example, try

main()
{
    int intvar;
    printf ("In C, we get %d\n", intvar = (630.0 / 100 * 60));
}

and you will get the exact same result (378).  Informix-4GL differs from
C only in that C will not promote beyond integer if no floats / doubles
are used; 4GL will promote scale depending on the type of operation in
an effort to retain accuracy according to the rules on page 1-14R.


-- 
 Alan S. Denney  |  Informix Software, Inc.  |  {pyramid|uunet}!infmx!aland
 Disclaimer: These opinions are mine alone.  If I am caught or killed,
             the secretary will disavow any knowledge of my actions.
 Santos' 4th Law: "Anything worth fighting for is worth fighting *dirty* for"