From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <775b8d190512152138g7ffaa837oe193f1556392a721@mail.gmail.com>
Date: Fri, 16 Dec 2005 16:38:16 +1100
From: Bruce Ellis <bruce.ellis@gmail.com>
To: erik quanstrom <quanstro@speakeasy.net>,
	Fans of the OS Plan 9 from Bell Labs <9fans@cse.psu.edu>
Subject: Re: [9fans] More Microsoft bashing
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	<20051216045115.GC15067@augusta.math.psu.edu>
	<20051216050214.GD15067@augusta.math.psu.edu>
	<20051216053346.F1BC41B12F7@dexter-peak.quanstro.net>
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horseshitt.  read.

brucee

On 12/16/05, erik quanstrom <quanstro@quanstro.net> wrote:
> you've got to take you're math cap off, and put your cs cap on.
>
> the motivation for defining MOD and DIV is so you can do somethign
> like this
>
>        row =3D size  DIV columns
>        col   =3D size MOD columns
>
> the pseudo-mathematics is applied ex post facto. clearly you have to
> get a single value out of the operation but that value is never going to
> be a member of Z. it's going to be a n-bit binary integer. also,
>
> ; cat > /tmp/fu.c
> int main(void){
>        int x;
>
>        x =3D 1 % 0;
> }
> /tmp/fu.c: In function `main':
> /tmp/fu.c:4: warning: division by zero
>
> - erik
>
>
> Dan Cross <cross@math.psu.edu> writes
>
> |
> | On Thu, Dec 15, 2005 at 11:51:15PM -0500, Dan Cross wrote:
> | > On Thu, Dec 15, 2005 at 08:04:02PM -0800, Jack Johnson wrote:
> | > > So, what *is* -5 MOD 3?
> | >
> | > Well, in general, it depends.
> | >
> | > Do you care whether the result a set or an integer?  The definitions =
due
> | > to Wirth et al are the former, while the MS definition appears to be =
the
> | > latter.
> |
> | Hmm, I guess on further reflection I ought to explain what I mean by
> | this before someone jumps all over me.
> |
> | The definition as per Wirth et al gives you a positive generator for an
> | equivalence class on Z, whereas the microsoft definition gives you the
> | definition of the division function extended to all of Z, which yields
> | an integer; the former definition is probably more comfortable for a
> | mathematician, and more what one would expect.  The latter is more
> | comfortable for someone who just wants to write a program.  In neither
> | case does this have much to do with the actual implementation (that is
> | to say, it's not like DIV actually gives you back an object
> | representing the set of all integers congruent to 0 modulo some integer
> | in Pascal), but only how that language interprets the definitions.
> |
> | > Regardless, all these definitions are problematic.  No where does it =
say
> | > they're defined only on Z*; what if Y is 0?
> |
> | This is still a problem.  You really want a function f: Z x Z* -> Z,
> | not f: Z x Z -> Z; that is, for f(x, y) =3D x div y, y should be non-ze=
ro.
> | Otherwise, it would be an absurdity.
> |
> |       - Dan C.
>