comp.lang.idl-pvwave archive: archive » bitwise operators in IDL?

Home » Public Forums » archive » bitwise operators in IDL?

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: bitwise operators in IDL? [message #25211 is a reply to message #25080]

Wed, 23 May 2001 12:46

John-David T. Smith is currently offline

John-David T. Smith
Messages: 384
Registered: January 2000

Senior Member

Craig Markwardt wrote:
>
> JD Smith <jdsmith@astro.cornell.edu> writes:
>> Marc Schellens wrote:
>>> To late for short circuitry.
>>> Consider a case when the second function in the if case
>>> has a side effect (e.g. modifying a global variable).
>>> After once defining the language this way, to change it
>>> would mean to introduce incopatibility.
>>
>> Not if you introduce another operator set all together for short
>> circuiting. People will use them increasingly, and AND,OR will go back
>> to being used primarily for their bitwise function, as they should be.
>> Sort of like C has "&&" and "&". I can't think of good replacement
>> names (I assume RSI won't allow the sensible && and ||). Ideas? (ANDS?
>> ORS?).
>>
>> JD
>
> I like the idea of short-circuiting logical operators as well. Some
> time ago I proposed LAND and LOR (for Logical-AND and Logical-OR). Of
> course what do you do about backwards compatibility? Namely people
> who have written code with their own LAND or ANDS variables. Imagine
> this :-)
>
> if LAND LAND 1 then ...
>
> What would it mean?
>
> Also, short-circuiting operators are not well-defined for vector
> operands. With vector operands it is possible in an
> element-by-element comparison for one element to evaluate true, while
> the other evaluates false. E.g.
>
> if [1,1] LAND [0,1] then ...
>
> So, both of these issues would at least have to be dealt with, and my
> guess is that the RSI folks will decide not to deal with it. Still, I
> think it's worth exploring.

Luckily, this is already illegal:

IDL> if [1,1] AND [0,1] then print, 'yay'
% Expression must be a scalar in this context: <INT Array[2]>.
% Execution halted at: $MAIN$

Only scalars allowed in if's. As long as the new lAND and lOR operators
are only allowed within if statements, no trouble arises.

For your example, proper use of total() is encouraged.

JD

Report message to a moderator

[Message index]

		bitwise operators in IDL? By: Rick Towler on Fri, 18 May 2001 14:34
		Re: bitwise operators in IDL? By: marc schellens[1] on Tue, 22 May 2001 22:14
		Re: bitwise operators in IDL? By: John-David T. Smith on Wed, 23 May 2001 08:16
		Re: bitwise operators in IDL? By: John-David T. Smith on Tue, 22 May 2001 14:00
		Re: bitwise operators in IDL? By: Stein Vidar Hagfors H[1] on Thu, 24 May 2001 07:14
		Re: bitwise operators in IDL? By: John-David T. Smith on Wed, 23 May 2001 12:46
		Re: bitwise operators in IDL? By: Craig Markwardt on Wed, 23 May 2001 11:19

Previous Topic:	defining functions on-the-fly
Next Topic:	more IDL falls asleep

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Fri Oct 10 23:05:00 PDT 2025

Total time taken to generate the page: 2.55948 seconds