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Date: Mon, 30 Dec 2013 07:15:26 -0800
From: Richard Henderson <rth@twiddle.net>
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Subject: Re: [Qemu-devel] [PATCH 05/10] target-arm: A64: Add "Floating-point
 data-processing (3 source)" insns
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To: Peter Maydell <peter.maydell@linaro.org>, qemu-devel@nongnu.org
Cc: patches@linaro.org, Michael Matz <matz@suse.de>, Alexander Graf <agraf@suse.de>, Claudio Fontana <claudio.fontana@linaro.org>, Dirk Mueller <dmueller@suse.de>, Will Newton <will.newton@linaro.org>, Laurent Desnogues <laurent.desnogues@gmail.com>, =?ISO-8859-1?Q?Alex_Benn=E9e?= <alex.bennee@linaro.org>, kvmarm@lists.cs.columbia.edu, Christoffer Dall <christoffer.dall@linaro.org>

On 12/28/2013 01:49 PM, Peter Maydell wrote:
> +    /* These are fused multiply-add, and must be done as one
> +     * floating point operation with no rounding between the
> +     * multiplication and addition steps.
> +     * NB that doing the negations here as separate steps is
> +     * correct : an input NaN should come out with its sign bit
> +     * flipped if it is a negated-input.
> +     */
> +    if (o1 == true) {
> +        gen_helper_vfp_negs(tcg_op3, tcg_op3);
> +    }
> +
> +    if (o0 != o1) {
> +        gen_helper_vfp_negs(tcg_op1, tcg_op1);
> +    }
> +
> +    gen_helper_vfp_muladds(tcg_res, tcg_op1, tcg_op2, tcg_op3, fpst);

Do you really get the wrong result passing the appropriate
float_muladd_negate_* constant?

I realize that the A32 target doesn't do this either, but shouldn't that be
cleaned up?  It's certainly confusing to the reader, wondering why they aren't
used...


r~