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Date: Thu, 8 Jul 2004 20:33:27 -0700
From: David Schultz <das@FreeBSD.ORG>
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Subject: Re: cvs commit: src/lib/msun/src math.h
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On Fri, Jul 09, 2004, David Schultz wrote:
> das         2004-07-09 03:31:09 UTC
> 
>   FreeBSD src repository
> 
>   Modified files:
>     lib/msun/src         math.h 
>   Log:
>   Define the following macros in terms of [gi]cc builtins when the
>   builtins are available: HUGE_VAL, HUGE_VALF, HUGE_VALL, INFINITY,
>   and NAN.  These macros now expand to floating-point constant
>   expressions rather than external references, as required by C99.
>   Other compilers will retain the historical behavior.  Note that
>   it is not possible say, e.g.
>   #define HUGE_VAL        1.0e9999
>   because the above may result in diagnostics at translation time
>   and spurious exceptions at runtime.  Hence the need for compiler
>   support for these features.
>   
>   Also use builtins to implement the macros isgreater(),
>   isgreaterequal(), isless(), islessequal(), islessgreater(),
>   and isunordered() when such builtins are available.
>   Although the old macros are correct, the builtin versions
>   are much faster, and they avoid double-expansion problems.

The Intel compiler is too smart for its own good sometimes.
I kept wondering why, despite icc's lack of a __builtin_isgreater(),
it seemed to be using one anyway.  It turns out that it had done
some constant propagation and determined the value of my call to the
libm routine __fpclassifyd() statically.  Pretty spiffy.