linux-kernel - RE: [PATCH v4 2/5] nds32: Support FP emulation

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Message-ID: <f0d20a4682b740659f28184c1278ae7d@AcuMS.aculab.com>
Date:   Fri, 23 Nov 2018 10:53:37 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Vincent Chen' <vincentc@...estech.com>,
        "green.hu@...il.com" <green.hu@...il.com>,
        "arnd@...db.de" <arnd@...db.de>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Nickhu <nickhu@...estech.com>
Subject: RE: [PATCH v4 2/5] nds32: Support FP emulation

From: Vincent Chen
> Sent: 22 November 2018 03:15
> 
> The Andes FPU coprocessor does not support denormalized number handling.
> According to the specification, FPU generates a denorm input exception
> that requires the kernel to deal with this instrution operation when it
> encounters denormalized operands. Hence an nds32 FPU ISA emulator in the
> kernel is required to meet requirement.

What does the FPU generate for results near zero?
If it doesn't generate denormalised results (but does detect them)
then I assume it never generates FP values with exponent zero.
(So the gap around zero is even larger than it would be if exponent
zero values had a hidden bit.)
So is it really worth doing anything other than treating
denormalised values as zero?

	David

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