Re: [PATCH] libm/math: Use __math_xflow in obsolete math code

Keith Packard via Newlib <[email protected]> Mon, 03 Aug 2020 11:07:40 -0700

Newsgroups	gmane.comp.lib.newlib
Message-ID	<[email protected]>

Szabolcs Nagy <[email protected]> writes:

> note1: i used c99 code when i wrote the
> new math code and currently the old math
> code can be compiled with older compilers,
> this change might prevent that.

Hrm. I just learned about "#pragma STDC FENV_ACCESS on" this morning and
am wondering if we shouldn't just patch the old math library to use that
instead of calling the __math_xflow functions. Would be a simpler patch
and provide precise compatibility with the previous version.

Here's an example of how that works:

        #include <fenv.h>
        #include <stdio.h>

        #pragma STDC FENV_ACCESS on

        int main(void)
        {
                double x;
                int e;
                feclearexcept(FE_ALL_EXCEPT);
                x = 0.0 / 0.0;
                e = fetestexcept(FE_ALL_EXCEPT);
                printf("x %g e %x\n", x, e);
                return 0;
        }

$ cc except.c -lm
$ ./a.out
x -nan e 1
$

As you can see, even using constants still raise the appropriate
exception.

-- 
-keith

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