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Date: Wed, 27 Jan 2016 05:02:54 -0500
From: Hendrik Boom <hendrik@topoi.pooq.com>
To: caml-list@inria.fr
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Subject: Re: [Caml-list] truncated division, remainder and arithmetics

On Wed, Jan 27, 2016 at 01:34:47AM +0100, peio wrote:
> Good evening,
> 
> 
> while doing some modular arithmetic I discovered that OCaml uses the
> 'truncated division' convention for the `/` (quotient) operator.
> Actually this convention may seem innocent but it greatly affects the
> `mod` (remainder) operator: the sign of the result is the same as
> dividend.
> 
> After some research I realized that lots of people (D.Knuth!)
> criticized this convention in favor of floored division (sign of
> remainder same as divisor) or euclidean division (remainder always
> positive). I know such a key component of the language isn't likely to
> be changed but I would like to get some of the rationals behind this
> decision.

In the old days when all machines hadn't settled down to one true 
binary arithmetic convention, I noticed that the machines where the 
remainder had the same sign as the dividend were two's complement 
machines, and the ones where the remainder had the same sign as the 
divisor were one's complement machines.

-- hendrik