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From: Miguel Barao <mjsb@ramses.inesc-id.pt>
Organization: INESC-ID Lisboa
To: gentoo-science@lists.gentoo.org
Subject: Re: [gentoo-science] question about signbit
Date: Thu, 27 Oct 2005 15:24:54 +0100
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On Thursday 27 October 2005 13:52, Darren Dale wrote:
>
> Here is another test:
>
> #include <math.h>
> #include <stdio.h>
>
> int main() {
> 	printf("signbit(-1): %d\n", signbit(-1));
> 	printf("isnan(0.0/0): %d\n", isnan(0.0/0));
> 	printf("isinf(1.0/0): %d\n", isinf(1.0/0));
> 	return 0;
> }
>
> which yields:
>
> signbit(-1): -2147483648
> isnan(0.0/0): 1
> isinf(1.0/0): 1
>
> Do you know why signbit doesn't yield 1? 

The answer is in 'man signbit'.

signbit is probably just ANDing your float value with 2^31=0x80000000 which 
reads -2147483648 if considered as a signed int (like in your printf).

Miguel
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