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Re: -32768 [message #88106 is a reply to message #88104]

Thu, 20 March 2014 14:11

Jim Pendleton
Messages: 165
Registered: November 2011

Senior Member

On Thursday, March 20, 2014 11:01:01 AM UTC-6, Karl wrote:
> On Thursday, March 20, 2014 3:24:59 AM UTC-6, Rob Klooster wrote:
>
>> The reason it does not work, is that you first try to define +32768 and then negate the result. Since +32768 can only be expressed as a long, you end up with a long variable. Using fix is a solution, but you could also use the bitwise not operator, if you feel adventurous:
>
>>
>
>> IDL> a = not 32767
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>>
>
>> IDL> help, a
>
>>
>
>> A INT = -32768
>
>
>
> And whether this is a "bug" in IDL or not depends on how IDL defines literal constants.
>
>
>
> If an IDL (integral) constant has the form (excuse my abuse of regex):
>
>
>
> [+-][0-9]*
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>
>
> then one could argue this is be a bug.
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>
>
> If a constant can be only:
>
>
>
> [0-9]*
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>
>
> then, the '-' is taken as an operator and this would not be considered an IDL bug.
>
>
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> C allows:
>
>
>
> short a = -32768;
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>
>
> but warns about:
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> short a = -32769;
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>
>
> on a machine where a short is 16 bits.

The docs on numeric constants imply that the "+" and "-" are considered operators.

http://www.exelisvis.com/docs/Defining_and_Using_Const.html

This can also be tested experimentally by writing a DLM that checks if an input IDL_VARIABLE is an expression or a constant.

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[Message index]

		-32768 By: greg.addr on Tue, 18 March 2014 21:43
		Re: -32768 By: skymaxwell@gmail.com on Tue, 18 March 2014 22:02
		Re: -32768 By: Craig Markwardt on Wed, 19 March 2014 12:17
		Re: -32768 By: Rob Klooster on Thu, 20 March 2014 02:24
		Re: -32768 By: Karl[1] on Thu, 20 March 2014 10:01
		Re: -32768 By: Jim Pendleton on Thu, 20 March 2014 14:11
		Re: -32768 By: Yngvar Larsen on Thu, 20 March 2014 14:30
		Re: -32768 By: chris_torrence@NOSPAM on Thu, 20 March 2014 16:44
		Re: -32768 By: Yngvar Larsen on Fri, 21 March 2014 11:02
		Re: -32768 By: Yngvar Larsen on Fri, 21 March 2014 11:04
		Re: -32768 By: Lajos Foldy on Fri, 21 March 2014 11:16
		Re: -32768 By: Yngvar Larsen on Fri, 21 March 2014 11:39
		Re: -32768 By: Lajos Foldy on Fri, 21 March 2014 12:55
		Re: -32768 By: Dick Jackson on Sat, 22 March 2014 13:20
		Re: -32768 By: Lajos Foldy on Sat, 22 March 2014 13:58
		Re: -32768 By: Dick Jackson on Sat, 22 March 2014 16:56

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