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Date: Mon, 18 May 1998 10:03:53 +0200

Message-Id: <199805180803.KAA00738@pc85.lri.fr>

From: Jean-Christophe Filliatre <Jean-Christophe.Filliatre@lri.fr>

To: N Hur <mapnh@maths.bath.ac.uk>

Subject: Re: Is this OK?

In-Reply-To: <Pine.SUN.3.91.980515135653.27393A-100000@thor.maths.bath.ac.uk>

*> (* a camllight session *)
*

*>
*

*> #(-234)/4
*

*> ;;
*

*> - : int = -58
*

*>
*

*>
*

*> #div_big_int (big_int_of_string "-234") (big_int_of_string "4");;
*

*> - : big_int = -59
*

There is OK. Indeed, when defining the quotient and the remainder you

must specify the range of the remainder. Usually, you specify that the

remainder of the division of a by b is between 0 and b-1, whatever is

the sign of a. That is the case in the big_in library.

But in the case of Caml division, the specification is different: the

remainder has the same sign that a, which is negative in your example.

But in both cases you always have

a = b * (a/b) + (a mod b)

which is the expected invariant.

-- Jean-Christophe FILLIATRE mailto:Jean-Christophe.Filliatre@lri.fr http://www.lri.fr/~filliatr

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