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References: <20171211125705.16120-1-alex.bennee@linaro.org>
	<20171211125705.16120-20-alex.bennee@linaro.org>
From: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <a3fbf87d-e898-d2a7-6dab-2615dfe60939@linaro.org>
Date: Mon, 18 Dec 2017 15:26:31 -0800
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Subject: Re: [Qemu-devel] [PATCH v1 19/19] fpu/softfloat: re-factor compare
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To: =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>, peter.maydell@linaro.org, laurent@vivier.eu, bharata@linux.vnet.ibm.com, andrew@andrewdutcher.com, aleksandar.markovic@imgtec.com
Cc: qemu-devel@nongnu.org, Aurelien Jarno <aurelien@aurel32.net>

On 12/11/2017 04:57 AM, Alex Bennée wrote:
> +    if (a.cls == float_class_zero || b.cls == float_class_zero) {
> +        if (a.cls == float_class_normal) {
> +            return a.sign ? float_relation_less : float_relation_greater;
> +        } else if (b.cls == float_class_normal) {
> +            return b.sign ? float_relation_greater : float_relation_less;
> +        } else if (a.cls == b.cls) {
> +            return float_relation_equal;
> +        }
> +    }

This misses out on infinity handling, which should be like normals.
Perhaps better as

    if (a.cls == float_class_zero) {
        if (b.cls == float_class_zero) {
            return float_relation_equal;
        }
        return b.sign ? float_relation_greater : float_relation_less;
    } else if (b.cls == float_class_zero) {
        return a.sign ? float_relation_less : float_relation_greater;
    }

> +    /* The only infinity we need to explicitly worry about is
> +     * comparing two together, otherwise the max_exp/sign details are
> +     * enough to compare to normal numbers
> +     */

I don't think it's wise to rely on the contents of .exp for float_class_inf.
Really, the only valid member for that type is sign.  Better as

    if (a.cls == float_class_inf) {
        if (b.cls == float_class_inf) {
            if (a.sign == b.sign) {
                return float_relation_equal;
            }
        }
        return a.sign ? float_relation_less : float_relation_greater;
    } else if (b.cls == float_class_inf) {
        return b.sign ? float_relation_less : float_relation_greater;
    }


r~