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From: brnstnd@kramden.acf.nyu.edu (Dan Bernstein)
Newsgroups: comp.lang.c
Subject: Re: % operator with negatives
Message-ID: <2882:Dec1618:47:3190@kramden.acf.nyu.edu>
Date: 16 Dec 90 18:47:31 GMT
References: <1990Dec12.205416.26622@zoo.toronto.edu> <7461:Dec1310:04:0990@kramden.acf.nyu.edu> <1529@bbxsda.UUCP>
Organization: IR
Lines: 18

In article <1529@bbxsda.UUCP> scott@bbxsda.UUCP (Scott Amspoker) writes:
> In article <7461:Dec1310:04:0990@kramden.acf.nyu.edu> brnstnd@kramden.acf.nyu.edu (Dan Bernstein) writes:
> >And if you're asking ``Where is the information on it?'', the answer is
> >that a % b is defined so that (a / b) * b + (a % b) equals a. It's the
> >ambiguous definition of / that makes % so useless with negatives.
> Well I can really stir up the muck by pointing out that, by definition,
>     a mod 0 == a

We are (unfortunately) not talking about the mathematical mod function.
We are talking about the C % function.

I have never seen a sane use of remainders outside [0,b), b positive.
I have never seen a program use remainders for b negative. It's a shame
that no popular programming language has a mod function defined only for
b positive and guaranteed to be between 0 and b - 1 inclusive, as this
would strike the right balance between portability and efficiency.

---Dan