comp.lang.idl-pvwave archive: archive

Home » Public Forums » archive » -32768

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

Re: -32768 [message #88131 is a reply to message #88122]

Sat, 22 March 2014 13:20

Dick Jackson
Messages: 347
Registered: August 1998

Senior Member

On Friday, March 21, 2014 11:02:08 AM UTC-7, Yngvar Larsen wrote:
> On Friday, 21 March 2014 00:44:17 UTC+1, Chris Torrence wrote:
>> On Thursday, March 20, 2014 3:30:49 PM UTC-6, Yngvar Larsen wrote:
>
>> Jim P. is correct that the minus sign is really an operator. So it really is a runtime error to write "a = 32768s", regardless of whether you are then going to take the negative of it.
>
>
>
> Fair enough. In that case, what is missing is a way to enter a literal negative number. "-376768" _is_ a valid 16-bit signed integer after all! Not really a problem, since negation of a single number hardly is a big performance hit... Also, the OPs problem hasn't hit me at all during the 15+ years I've been using IDL. And there are at least 3 simple (bit silly) workarounds, already mentioned in this thread.

And for our further pedantry, if you really need to know which is most time efficient (at least on my MacBook, IDL 8.2):

IDL> tic & for i=1,1e7 do a=FIX(-32768) & toc
% Time elapsed: 1.7954290 seconds.

IDL> tic & for i=1,1e7 do a=FIX('8000'X) & toc ; Hex code depends on hardware "endian-ness"
% Time elapsed: 1.4319592 seconds.

IDL> tic & for i=1,1e7 do a=not 32767S & toc
% Time elapsed: 1.1942451 seconds.

IDL> tic & for i=1,1e7 do a=-32767S-1S & toc ; The winner!
% Time elapsed: 1.1435649 seconds.

Notice how much longer this takes compared to a simple, positive literal:

IDL> tic & for i=1,1e7 do a=32767S & toc
% Time elapsed: 0.39454412 seconds.

Cheers,
-Dick

Dick Jackson Software Consulting Inc.
Victoria, BC, Canada --- www.d-jackson.com

Report message to a moderator

[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

Previous Topic:	Killing Widget Objects
Next Topic:	How to choose the pixels along a curve in an image

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Wed Oct 08 15:49:41 PDT 2025

Total time taken to generate the page: 0.00208 seconds