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Re: Basic Math: I _hope_ this is a stupid question [message #43789 is a reply to message #43754]

Mon, 25 April 2005 05:44

btt
Messages: 345
Registered: December 2000

Senior Member

David Fanning wrote:
> Ed Hyer writes:
>
>
>> IDL> print,288*180
>> -13696
>> IDL> print,long(288*180)
>> -13696
>> IDL> print,ulong64(288*180)
>> 18446744073709537920
>> IDL> print,288.*180
>> 51840.0
>>
>> I just want to multiply two integers! Is that so wrong?
>
>
> Here are a couple of articles for you:
>
> http://www.dfanning.com/math_tips/sky_is_falling.html
> http://www.dfanning.com/math_tips/double.html
>
> Where you see "double" you should read "long integer", and where
> you see "float" you should read "integer".
>
> Basically, casting a short multiplication (288*180) to a
> long *after* you do the arithmetic, doesn't gain you
> anything. You have to do it *before* you to the arithmetic. :-)
>

Hi,

You might also consider using the COMPILE_OPT compile flag DEFINT32 at
the beginning of your routines. I have taken Mark Hadfield's
recommendation to heart and now use COMPILE_OPT IDL2 pretty much everywhere.

Cheers,
Ben

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[Message index]

		Re: Basic Math: I _hope_ this is a stupid question By: MarioIncandenza on Wed, 27 April 2005 16:14
		Re: Basic Math: I _hope_ this is a stupid question By: Geoff Cureton on Wed, 27 April 2005 09:26
		Re: Basic Math: I _hope_ this is a stupid question By: btt on Mon, 25 April 2005 05:44
		Re: Basic Math: I _hope_ this is a stupid question By: David Fanning on Sun, 24 April 2005 14:48
		Re: Basic Math: I _hope_ this is a stupid question By: K. Bowman on Thu, 28 April 2005 06:15

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