x86 Denormal flag

[Michael Morrell <mmorrell@tachyum.com>]

Should fetestexcept be able to test for the denormal flag in the MXCSR?

My test case is:

define _GNU_SOURCE
#include <fenv.h>
#include <stdio.h>
#include <xmmintrin.h>

volatile float two = 2.0f;
volatile float den = 0x1.0p-130;

int main()
{
    volatile float r;

    r = den / two;

    if (_mm_getcsr() & _MM_EXCEPT_DENORM)
                printf("mxcsr has DENORM bit set\n");
    if (fetestexcept(__FE_DENORM))
                printf("DENORM is set\n");
    return 0;
}

And it shows that the Denormal flag is set in MXCSR, but fetestexcept returns 0 here.

It seems like fetestexcept only works for the 5 standard IEEE flags, but then why is __FE_DENORM even defined?

   Michael