From: Richard Henderson <rth@twiddle.net>
To: Peter Maydell <peter.maydell@linaro.org>, qemu-devel@nongnu.org
Cc: Tom Musta <tommusta@gmail.com>, patches@linaro.org
Subject: Re: [Qemu-devel] [PATCH] softfloat: Fix factor 2 error for scalbn on denormal inputs
Date: Fri, 20 Dec 2013 09:34:47 -0800 [thread overview]
Message-ID: <52B47FB7.2030409@twiddle.net> (raw)
In-Reply-To: <1387490251-15944-1-git-send-email-peter.maydell@linaro.org>
On 12/19/2013 01:57 PM, Peter Maydell wrote:
> If the input to float*_scalbn() is denormal then it represents
> a number 0.[mantissabits] * 2^(1-exponentbias) (and the actual
> exponent field is all zeroes). This means that when we convert
> it to our unpacked encoding the unpacked exponent must be one
> greater than for a normal number, which represents
> 1.[mantissabits] * 2^(e-exponentbias) for an exponent field e.
>
> This meant we were giving answers too small by a factor of 2 for
> all denormal inputs.
>
> Note that the float-to-int routines also have this behaviour
> of not adjusting the exponent for denormals; however there it is
> harmless because denormals will all convert to integer zero anyway.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
At least the float128 routine needs the same fix.
I'm less certain about the floatx80 routine, since IIRC
that format has no implicit 1 bit -- it's always explicit.
r~
next prev parent reply other threads:[~2013-12-20 17:35 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-19 21:57 [Qemu-devel] [PATCH] softfloat: Fix factor 2 error for scalbn on denormal inputs Peter Maydell
2013-12-20 17:34 ` Richard Henderson [this message]
2013-12-20 17:48 ` Peter Maydell
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