[Info-vax] decrementing & for loops in C

[Bill Gunshannon]

In article <wOqdnW_z16MLEPrUnZ2dnUVZ_qLinZ2d at giganews.com>,
	"Richard B. Gilbert" <rgilbert88 at comcast.net> writes:
> Bill Gunshannon wrote:
>> In article <RBJ9l.9487$cu.6865 at news-server.bigpond.net.au>,
>> 	"Tim E. Sneddon" <tesneddon at bigpond.com> writes:
>>> Bill Gunshannon wrote:
>>>> In article <49667A6E.3050507 at nowhere.com>,
>>>> 	nobody <nobody at nowhere.com> writes:
>>>>> Turning off optimization should normally cause the program to execute 
>>>>> your program exactly as written.
>>>> A program should always execute exactly as written.  No machine is smart
>>>> enough to second guess the intent of a human.
>>>>
>>> That is arguable. After your code has been optimised
>>> it doesn't quite execute 'exactly as written'. The
>>> end result might be 'exactly as written'. However, the
>>> path to get there has been completely shuffled around
>>> by the compiler.
>> 
>> Well, let's be clear on this.  By "exactly as written" I mean just what it
>> says.  Not "as the writer intended", but "exactly as written".  That allows
>> for optimizing out code that would never be executed because I wrote the 
>> code wrong, like the original example.  It may not be what I wanted, but
>> it is what I wrote.  But, the system should not be changing the order of
>> operations for any code I wrote because it has absolutely no way of
>> determining that there was not a particular reason for doing it in that
>> order.  No machine (or compiler) is that smart.  Someone mentioned Ada
>> doing this in an earlier post.  Knowing what the primary purposes of Ada
>> are, that would really scare me.
>> "Let's see.  The programmer wants me to check for weight on the wheel
>>  struts before raising the landing gear.  but I think it would be much
>>  more efficient to raise the gear first."   :-)
>> 
>> What, you say that's just silly.  How about this?
>> 
>> {
>>    int thrust_reversers, power_level;
>> 
>> { thrust_reversers = 10; power_level = 20; }
>> }
>> 
>> Does the order of these two (apparently) equal operations make a difference?
> 
> Possibly.  If you accept the implied context of an aircraft about to 
> land it could make a major difference.  Since the largest thing I ever 
> flew was a de Haviland Beaver (L-20) which wasn't so equipped, I can't 
> offer more than a SWAG!
> 
>> Can a machine determine that?
> 
> No!  But I wouldn't ask one to do so!  

There are people here saying they do.  They specifically pointed out
Ada as a language where this is common in compilers.  And, as I stated,
knowing the primary uses for Ada, I would be very afraid.

>                                        If you WOULD, please stay well 
> clear of me, my family, and my property!  And keep your machine and 
> anything it controls well clear too!!!
 
I think you missed something along the way.  I'm the one who doesn't
want any machines making any changes to my programs.  Compile what I
wrote, mistakes and all.  I'll fix them.  But no machine should ever
assume it knows more about my job than I do.  :-)

bill 

-- 
Bill Gunshannon          |  de-moc-ra-cy (di mok' ra see) n.  Three wolves
billg999 at cs.scranton.edu |  and a sheep voting on what's for dinner.
University of Scranton   |
Scranton, Pennsylvania   |         #include <std.disclaimer.h>