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s390x/tcg: Hide IEEE underflows in some scenarios

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IEEE underflows are not reported when the mask bit is off and we don't
also have an inexact exception.

z14 PoP, 9-20, "IEEE Underflow":
    An IEEE-underflow exception is recognized for an
    IEEE target when the tininess condition exists and
    either: (1) the IEEE-underflow mask bit in the FPC
    register is zero and the result value is inexact, or (2)
    the IEEE-underflow mask bit in the FPC register is
    one.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20190218122710.23639-6-david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
This commit is contained in:
David Hildenbrand 2019-02-18 13:27:00 +01:00 committed by Cornelia Huck
parent fcb9e9f2a1
commit 6d6ad1d14e
1 changed files with 13 additions and 0 deletions
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13
target/s390x/fpu_helper.c
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@ -63,6 +63,19 @@ static void handle_exceptions(CPUS390XState *env, uintptr_t retaddr)
env->fpu_status.float_exception_flags = 0;
s390_exc = s390_softfloat_exc_to_ieee(qemu_exc);
/*
* IEEE-Underflow exception recognition exists if a tininess condition
* (underflow) exists and
* - The mask bit in the FPC is zero and the result is inexact
* - The mask bit in the FPC is one
* So tininess conditions that are not inexact don't trigger any
* underflow action in case the mask bit is not one.
*/
if (!(s390_exc & S390_IEEE_MASK_INEXACT) &&
!((env->fpc >> 24) & S390_IEEE_MASK_UNDERFLOW)) {
s390_exc &= ~S390_IEEE_MASK_UNDERFLOW;
}
/*
* FIXME:
* 1. Right now, all inexact conditions are inidicated as