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Re: AC_C_LONG_DOUBLE is wrong on IRIX 5.3

From: Oliver Kiddle
Subject: Re: AC_C_LONG_DOUBLE is wrong on IRIX 5.3
Date: Tue, 13 Nov 2001 15:50:00 +0000

Paul Eggert wrote:
> That sounds reasonable.  Can you please resubmit a patch along those lines?
> You'd have to change the documentation as well, of course.

Yes, I'll submit a new patch shortly but first I have a question about

> Also, the patch should compare DBL_MAX to LDBL_MAX (defined in
> float.h).  This can be done at compile-time.  This will catch some of
> the counterexamples that I am thinking of.  If an implementation
> doesn't have float.h, DBL_MAX and LDBL_MAX, we should play it safe and
> assume it doesn't have 'long double'.

How can I compare DBL_MAX and LDBL_MAX at compile-time? I was thinking
that you meant for me to use a #if directive but floating point numbers
don't appear to be allowed in #if expressions. So am I missing something
or does this need a runtime check?

To catch float.h being missing, can I just #include it and rely on the
failure of the C compiler to force a negative result to the test?

> The patch shouldn't check for %Lf, though.  That's a runtime check,
> and should be a different macro (if it's a macro at all).

Yes, it could clearly be different as long double's size/existence is
determined by the compiler while %Lf is determined by libc.

Thanks and sorry for my slow response on this.


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