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From: Richard Henderson <richard.henderson@linaro.org>
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Date: Tue, 13 Feb 2018 07:39:39 -0800
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Subject: Re: [Qemu-devel] [PATCH v4 13/22] fpu/softfloat: re-factor mul
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To: Peter Maydell <peter.maydell@linaro.org>, =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>
Cc: Laurent Vivier <laurent@vivier.eu>, bharata@linux.vnet.ibm.com, Andrew Dutcher <andrew@andrewdutcher.com>, QEMU Developers <qemu-devel@nongnu.org>, Aurelien Jarno <aurelien@aurel32.net>

On 02/13/2018 07:20 AM, Peter Maydell wrote:
>> +static FloatParts mul_floats(FloatParts a, FloatParts b, float_status *s)
>> +{
>> +    bool sign = a.sign ^ b.sign;
>> +
>> +    if (a.cls == float_class_normal && b.cls == float_class_normal) {
>> +        uint64_t hi, lo;
>> +        int exp = a.exp + b.exp;
>> +
>> +        mul64To128(a.frac, b.frac, &hi, &lo);
> 
> It seems a shame that we previously were able to use a
> 32x32->64 multiply for the float32 case, and now we have to
> do an expensive 64x64->128 multiply regardless...

To be fair, I've proposed two different solutions addressing that -- c++
templates and glibc macros -- and you like neither.  Is there a third
alternative that does not involve code duplication?


r~