From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=0.7 required=5.0 tests=BAYES_00,FREEMAIL_FROM,
	FREEMAIL_REPLYTO,REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no
	version=3.4.4
X-Google-Thread: a07f3367d7,78ff7923606282ea
X-Google-Attributes: gida07f3367d7,public,usenet
X-Google-NewGroupId: yes
X-Google-Language: ENGLISH,ASCII-7-bit
X-Received: by 10.180.106.232 with SMTP id gx8mr172711wib.2.1366858345917;
        Wed, 24 Apr 2013 19:52:25 -0700 (PDT)
Path: 
 hg5ni24017wib.1!nntp.google.com!feeder1.cambriumusenet.nl!feed.tweaknews.nl!194.109.133.81.MISMATCH!newsfeed.xs4all.nl!newsfeed2.news.xs4all.nl!xs4all!border4.nntp.ams.giganews.com!border2.nntp.ams.giganews.com!border3.nntp.ams.giganews.com!border1.nntp.ams.giganews.com!nntp.giganews.com!rt.uk.eu.org!de-l.enfer-du-nord.net!feeder1.enfer-du-nord.net!newsfeed.eweka.nl!eweka.nl!feeder3.eweka.nl!212.23.6.68.MISMATCH!zen.net.uk!hamilton.zen.co.uk!reader01.nrc01.news.zen.net.uk.POSTED!not-for-mail
From: Phil Thornley <phil.jpthornley@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: SPARK - division by zero problem
Date: Thu, 18 Apr 2013 09:35:48 +0100
Message-ID: <MPG.2bd9c09a49da8ab39896a4@news.zen.co.uk>
References: <0dbac307-0c0c-4883-8644-d1ffc25419f8@googlegroups.com>
Reply-To: phil.jpthornley@gmail.com
MIME-Version: 1.0
User-Agent: MicroPlanet-Gravity/3.0.4
Organization: Zen Internet
NNTP-Posting-Host: 70bc4af4.news.zen.co.uk
X-Trace: 
 DXC=[UcCf57aB8bIgV_m`EU;eoa0UP_O8AJol=dR0\ckLKG`WeZ<[7LZNRf1IKCnlfP7odUhLi?]0KG=k>9Ld44A[H=k30FehBjPbWa
X-Complaints-To: abuse@zen.co.uk
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Date: 2013-04-18T09:35:48+01:00
List-Id: <comp.lang.ada>

In article <0dbac307-0c0c-4883-8644-d1ffc25419f8@googlegroups.com>, 
see.my.homepage@gmail.com says...
> 
> While playing with SPARK (I also agree that comp.lang.ada is adequate for SPARK content) I have found a problem that can be shown in the following stripped-down example:
> 
> <my_package.ads>
> package My_Package is
> 
>     procedure Divide (X : in Integer; Y : in Integer; Z : out Integer);
>     --# derives Z from X, Y;
>     --# pre Y /= 0;
>     --# post Z = X / Y;
> 
> end My_Package;
> 
> <my_package.adb>
> package body My_Package is
> 
>     procedure Divide (X : in Integer; Y : in Integer; Z : out Integer) is
>     begin
>         Z := X / Y;  -- this is line 5
>     end Divide;
> 
> end My_Package;
> 
> In this example I would expect the VC associated with rtc on line 5 above to be discharged based on the hypothesis from Divide's precondition: that is, Y is known to be non-zero, so division by zero in line 5 cannot happen.
> 
> Tools are invoked in the following order:
> 
> $ sparkmake
> $ spark -index_file=spark.idx -vcg -config_file=config.cfg -output_dir=spark my_package.adb
> $ sparksimp
> $ pogs
> 
> The summary says that the VC in question in undischarged.
> Is there anything missing?
> 
> The tools come from Ubuntu packages and announce themselves as GPL 2011.

The undischarged VC I get is:
procedure_divide_1.
H1:    y <> 0 .
H2:    x >= - 2147483648 .
H3:    x <= 2147483647 .
H4:    y >= - 2147483648 .
H5:    y <= 2147483647 .
H6:    integer__size >= 0 .
       ->
C1:    x div y <= 2147483647 .

which is false for x = -2147483648, y = -1

Cheers,

Phil