Re: [BLACKBOX] Math.Pi (was: CONSTant expressions)

From: Campbell, Robert D (SELEX) (UK Edinburgh) <"Campbell,>
Date: Mon, 21 Jan 2008 09:19:42 -0000

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Hi Chris

I'm replying personally as I suspect I have sounded off
more than enough in public.

You are right, what I say is 'theory' & supposition. None
of it is actual knowledge.

I did not say the Math.Pi behaviour was intentional. I have no idea.

I wrote my own Pi procedure:

PROCEDURE Pi (x : REAL) : REAL;
  BEGIN
    RETURN Math.Pi (x)
  END Pi;

It behaved like Math.Pi. (ie pi # Pi)


 I rewrote it as
  RETURN 22. / 7.

and now pi does = Pi.

Another hole in my 'theory'.


I first noticed pi # Pi about 10 years ago! I vaguely remember
investigating
this at the time and discovering that Pi was more accurate than pi. But
my memory could be playing me tricks.


Cheers

Robert

ps - I decided to go public on this anyway!


>> -----Original Message-----
>> From: BlackBox [mailto:BLACKBOX{([at]})nowhere.xy
>> Of CFB Software
>> Sent: 20 January 2008 23:41
>> To: BLACKBOX{([at]})nowhere.xy
>> Subject: Re: [BLACKBOX] Math.Pi (was: CONSTant expressions)
>>
>> *** WARNING ***
>>
>> This mail has originated outside your organization, either
>> from an external partner or the Global Internet.
>> Keep this in mind if you answer this message.
>>
>> >From: BlackBox [mailto:BLACKBOX{([at]})nowhere.xy
>> >Sent: Sunday, 20 January 2008 11:16 PM
>> >To: BLACKBOX{([at]})nowhere.xy
>> >Subject: Re: [BLACKBOX] CONSTant expressions
>> >
>> >> CFB Software wrote:
>> >> OutBool ('pi = Pi ? ', pi = Math.Pi ()); (*
>> FALSE *)
>> >>
>> >> I would have expected the third result to be TRUE - have I fallen
>> >> into a carefully-laid trap?
>> >
>> > The call Math.Pi () leaves an 80-bit result in the floating point
>> >register, that is then compared with a 64-bit rounded
>> version. Result?
>> >they are different!
>>
>> I'm not convinced that the behaviour is intentional. Math.Pi
>> is documented as *returning* a REAL. i.e. 64 bits.
>>
>> Additionally, how does your theory explain this one?
>>
>> OutBool ('Pi = Pi ? ', Math.Pi() = Math.Pi()
>> ); (* FALSE *)
>>
>> Regards,
>> Chris
>>
>> Chris Burrows
>> CFB Software
>> http://www.cfbsoftware.com/cp
>>
>>
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>> To unsubscribe, send a message with body "SIGNOFF BLACKBOX"
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>>

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Received on Mon Jan 21 2008 - 10:19:42 UTC