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List:       freebsd-standards
Subject:    Re: signbit() implementation question
From:       Bruce Evans <bde () zeta ! org ! au>
Date:       2003-02-10 19:25:21
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On Mon, 10 Feb 2003, Mike Barcroft wrote:

> I'm wondering if any casts from float->double or long double->double
> will cause the sign-bit to change.  In my implementation I just have
> the macro pass its argument to a function that takes a double for its
> argument.  In the tests I've done the sign-bit never changes with
> these casts, but I don't know if this is guaranteed to work for all
> values or whether this is completely portable.

Preserving the sign bit in conversions and rounding, etc. is required
by at least ieee854 (section 6.3), so I think all reasonable hardware
preserves it.

Bruce


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