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References: <20180124131315.30567-1-alex.bennee@linaro.org>
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From: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <bf12b90b-d3a2-5973-6e66-9b13dcc3d38e@linaro.org>
Date: Wed, 24 Jan 2018 09:34:42 -0800
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Subject: Re: [Qemu-devel] [PATCH v3 22/22] fpu/softfloat: re-factor sqrt
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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
Cc: qemu-devel@nongnu.org, Aurelien Jarno <aurelien@aurel32.net>

On 01/24/2018 05:13 AM, Alex Bennée wrote:
> +/*
> + * Returns an approximation to the square root of the fraction given
> + * by `a'. Considered as an integer, `a' must be at least 2^31. If bit
> + * 0 of `aExp' (the least significant bit) is 1, the integer returned
> + * approximates 2^31*sqrt(`a'/2^31), where `a' is considered an
> + * integer. If bit 0 of `aExp' is 0, the integer returned approximates
> + * 2^31*sqrt(`a'/2^30). In either case, the approximation returned
> + * lies strictly within +/-2 of the exact value.
> + */

The commentary we copied from old softfloat is wrong.
We produce an exactly rounded result.

> +    if (a.cls >= float_class_qnan) {

is_nan.


r~