RE: [Caml-list] Integer arithmetic: mod

["Dave Berry" <Dave@kal.com>]

The Standard ML Basis Library also has both div/mod and rem/quot.  (This
was after some people complained that the original language definition
required the slower, Knuth-approved, behaviour).



-----Original Message-----
From: Marcin 'Qrczak' Kowalczyk [mailto:qrczak@knm.org.pl]
Sent: 04 August 2001 21:26
To: caml-list@inria.fr
Subject: Re: [Caml-list] Integer arithmetic: mod


Sat, 04 Aug 2001 11:48:07 -0700, Chris Hecker <checker@d6.com> pisze:

> Most computer languages (and chips) simply say "(a/b)*b + a mod b =
> a" and leave it at that.

Fortunately not all, e.g. in Python (-123) % 10 == 7. In C89 the
behavior for negative numbers was left implementation-defined but
in C99 it is specified as truncation towards 0.

> Unfortunately, people (and language and chip designers) assume
> (-4)/3 = -1 (truncate towards zero) rather than -2 (floor),

Not all people: Donald Knuth clearly disagrees. He has written
something along the lines "beware of programming languages which use
a different definition than the one which says (-4)/3 = -2".

Haskell has both: div & mod truncate downwards, quot & rem truncate
towards 0.

-- 
 __("<  Marcin Kowalczyk * qrczak@knm.org.pl http://qrczak.ids.net.pl/
 \__/
  ^^                      SYGNATURA ZASTĘPCZA
QRCZAK

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