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Re: What is wrong with Bugzilla? [Was: Re: GCC and Floating-Point]
Vincent Lefevre <vincent+gcc@vinc17.org> writes:
> On 2005-05-31 15:33:48 +0200, Andreas Schwab wrote:
>> Vincent Lefevre <vincent+gcc@vinc17.org> writes:
>> > On 2005-05-31 14:27:01 +0200, Andreas Schwab wrote:
>> >> Vincent Lefevre <vincent+gcc@vinc17.org> writes:
>> >> > But as I said on my page, this isn't much a problem since users
>> >> > who really need *extended* precision can still set the rounding
>> >> > precision to extended precision; this isn't portable, but extended
>> >> > precision isn't portable anyway.
>> >>
>> >> What about LDBL_* from <float.h>?
>> >
>> > What do you mean here?
>>
>> They give you access to long double in a portable manner,
>
> No, this is not portable,
Sure they are, since they are required since C89.
> since if extended precision is necessary to get correct results for some
> application, the same application run on PowerPC, where there is no
> extended precision, would give incorrect results.
You can use <float.h> to find that out. That's what portability is about.
>> but if you change the rounding mode then the constants are no longer
>> accurate.
>
> The implementation could provide another way to get the necessary
> information; perhaps nextafterl()...
But you still have to take care of (1.0 + LDBL_EPSILON) != 1.0, or the
other required identities in <float.h>.
Andreas.
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Andreas Schwab, SuSE Labs, schwab@suse.de
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