From: David Hildenbrand <david@redhat.com>
To: Richard Henderson <richard.henderson@linaro.org>, qemu-devel@nongnu.org
Cc: alex.bennee@linaro.org, bharata@linux.ibm.com
Subject: Re: [PATCH 6/8] softfloat: Implement float128_muladd
Date: Fri, 25 Sep 2020 11:17:28 +0200 [thread overview]
Message-ID: <9ced60b8-41d3-5c81-cbe8-92f219ba6978@redhat.com> (raw)
In-Reply-To: <ad092b60-dd41-33f0-9530-75fba4309c3c@linaro.org>
On 24.09.20 15:30, Richard Henderson wrote:
> On 9/24/20 12:56 AM, David Hildenbrand wrote:
>> I do wonder if a type for Int256 would make sense - instead of > manually passing these arrays.
>
> I could do that. It does name better, I suppose, in passing. So long as
> you're happy having the guts of the type be public, and not wrapping everything
> like we do for Int128...
We can do that once we have hardware+compiler support for 256bit ;)
>
> Either is better than the softfloat style, which would pass 12 arguments to
> these helpers... ;-)
Indeed
>
>>> +static void shortShift256Left(uint64_t p[4], unsigned count)
>>> +{
>>> + int negcount = -count & 63;
>>
>> That's the same as "64 - count", right? (which I find easier to get)
>
> In this case, yes.
>
> Of course, more hosts have a "neg" instruction than they do a
> "subtract-from-immediate" instruction. When the shift instruction only
> examines the low N bits, the "& 63" is optimized away, so this can result in 1
> fewer instruction in the end.
>
> Which is why I almost always use this form, and it's already all over the code
> inherited from upstream.
>
>> Wow, that's a beast :)
>
> But not much worse than muladd_floats(), I'm pleased to say.
Definitely!
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-09-25 9:18 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-24 1:24 [PATCH 0/8] softfloat: Implement float128_muladd Richard Henderson
2020-09-24 1:24 ` [PATCH 1/8] softfloat: Use mulu64 for mul64To128 Richard Henderson
2020-09-24 7:32 ` David Hildenbrand
2020-09-24 1:24 ` [PATCH 2/8] softfloat: Use int128.h for some operations Richard Henderson
2020-09-24 7:35 ` David Hildenbrand
2020-09-24 1:24 ` [PATCH 3/8] softfloat: Tidy a * b + inf return Richard Henderson
2020-09-24 7:37 ` David Hildenbrand
2020-09-24 1:24 ` [PATCH 4/8] softfloat: Add float_cmask and constants Richard Henderson
2020-09-24 7:40 ` David Hildenbrand
2020-09-24 1:24 ` [PATCH 5/8] softfloat: Inline pick_nan_muladd into its caller Richard Henderson
2020-09-24 7:42 ` David Hildenbrand
2020-09-24 1:24 ` [PATCH 6/8] softfloat: Implement float128_muladd Richard Henderson
2020-09-24 7:56 ` David Hildenbrand
2020-09-24 13:30 ` Richard Henderson
2020-09-25 9:17 ` David Hildenbrand [this message]
2020-09-24 1:24 ` [PATCH 7/8] softfloat: Use x86_64 assembly for {add,sub}{192,256} Richard Henderson
2020-09-24 1:24 ` [PATCH 8/8] softfloat: Use aarch64 " Richard Henderson
2020-09-24 8:00 ` [PATCH 0/8] softfloat: Implement float128_muladd David Hildenbrand
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