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Re: [PATCH] powerpc: Fix logbl on power7 [BZ# 21280]
- From: "Tulio Magno Quites Machado Filho" <tuliom at linux dot vnet dot ibm dot com>
- To: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>, libc-alpha at sourceware dot org
- Cc:
- Date: Fri, 28 Apr 2017 14:59:14 -0300
- Subject: Re: [PATCH] powerpc: Fix logbl on power7 [BZ# 21280]
- Authentication-results: sourceware.org; auth=none
- References: <1490043778-30228-1-git-send-email-tuliom@linux.vnet.ibm.com> <50b87cce-2f3a-d84b-bc38-d81fa3623738@linaro.org> <87wpbi4ck0.fsf@totoro.br.ibm.com> <b22f1e69-55c3-88ae-a057-3983a9e89d52@linaro.org>
Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:
> On 21/03/2017 17:09, Tulio Magno Quites Machado Filho wrote:
>> Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:
>>
>>> On 20/03/2017 18:02, Tulio Magno Quites Machado Filho wrote:
>>>> 1. Fix the results for negative subnormals by ignoring the signal when
>>>> normalizing the value.
>>>> 2. Fix the output when the high part is a power of 2 and the low part
>>>> is a nonzero number with opposite sign. This fix is based on commit
>>>> 380bd0fd2418f8988217de950f8b8ff18af0cb2b.
>>>
>>> It is not a blocker, but based on the complexity of the change and the
>>> optimization real case usage, I wonder if it would be better to just remove
>>> it and use the default implementation instead.
>>
>> I tried to do that before fixing these, but the performance difference is
>> still around 2x.
>
> I would expect it, but the question is do we really care about the performance
> of logbl-ibm128 to maintain a separated implementation for power7+ only?
Yes, we still need it.
Considering your proposal was not a blocker, I plan to merge this fix.
Anyway, I agree in re-evaluating the removal of this optimization
in a few releases.
--
Tulio Magno