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From: jbs@yktvmv.watson.ibm.com
Subject: Re: Fortran or Ada?
Date: 1998/09/30
Message-ID: <19980930.153012.753@yktvmv.watson.ibm.com>#1/1
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References: <36068E73.F0398C54@meca.polymtl.ca>
 <slrn70dv6k.2qp.gisle@krake.ii.uib.no> <m3n27sqhms.fsf@visar.physast.uga.edu>
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 <360A3446.8AD84137@lmco.com> <6udre0$ha1$1@nnrp1.dejanews.com>
 <19980925.185359.250@yktvmv.watson.ibm.com> <6uifdr$dog$1@nnrp1.dejanews.com>
 <19980928.184428.604@yktvmv.watson.ibm.com>
 <wclodius-2909981741110001@clodius.lanl.gov>
 <19980929.214309.386@yktvmv.watson.ibm.com> <6utg60$h6l$1@nnrp1.dejanews.com>
Organization: IBM
Newsgroups: comp.lang.fortran,comp.lang.ada
Date: 1998-09-30T00:00:00+00:00
List-Id: <comp.lang.ada>

In article <6utg60$h6l$1@nnrp1.dejanews.com>,
 on Wed, 30 Sep 1998 14:45:20 GMT,
 dewarr@my-dejanews.com writes:
>In article <19980929.214309.386@yktvmv.watson.ibm.com>,
>  jbs@yktvmv.watson.ibm.com wrote:
>>          The accident report indicates that they deliberately
>> chose not to do it in this case because they were worried about
>> performance.  This would seem to indicate that turning off the
>> error check is not cheap (in terms of performance).
>>                   James B. Shearer
>
>
>This is incomprehensible. Turning off a check eliminates the code for the
>check and eliminates the performance penalty of the check. What are you
>trying to say here?

         Let me quote the accident report again:
!In the failure scenario, the primary technical causes are the Operand Error
!when converting the horizontal bias variable BH, and the lack of protection of
!this conversion which caused the SRI computer to stop.
!
!It has been stated to the Board that not all the conversions were protected
!because a maximum workload target of 80% had been set for the SRI computer. To
!determine the vulnerability of unprotected code, an analysis was performed on
!every operation which could give rise to an exception, including an Operand
!Error. In particular, the conversion of floating point values to integers was
!analysed and operations involving seven variables were at risk of leading to
!an Operand Error. This led to protection being added to four of the variables,
!evidence of which appears in the Ada code. However, three of the variables
!were left unprotected. No reference to justification of this decision was
!found directly in the source code. Given the large amount of documentation
!associated with any industrial application, the assumption, although agreed,
!was essentially obscured, though not deliberately, from any external review.

         It appears you do not turn off the check, instead you "protect"
the check which is expensive.
                        James B. Shearer