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Re: -32768 [message #88127 is a reply to message #88126]

Fri, 21 March 2014 11:39

Yngvar Larsen
Messages: 134
Registered: January 2010

Senior Member

On Friday, 21 March 2014 19:16:40 UTC+1, fawltyl...@gmail.com wrote:
> On Friday, March 21, 2014 7:02:08 PM UTC+1, Yngvar Larsen wrote:
>
>
>
>> For literals, I agree that this might be regarded as dubious. But in general, the fact that N-bit integer arithmetic is silently wrapped modulo 2^N should be regarded as semantically well defined. If not, I believe a serious performance hit would result.
>
> The C standard guarantees modulo 2^N arithmetic for unsigned integers only. For signed integers, the behavior is undefined.

Thanks for the info! I didn't know that. Fortunately, I haven't had to do much numerical work in C lately.

Do you by any chance know the rationale behind that?

> -32768 is a funny number. Did you know that its absolute value is negative?
>
> IDL> help, abs(-32767-1)
> <Expression> INT = -32768

Yes! In fact, we've been internally misusing that fact in an IDL routine at work :) I guess we probably shouldn't, but it worked to well in the context to leave it alone!

--
Yngvar

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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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