[U-Boot] [PATCH] arm: add 64-64 bit divider

[Che-liang Chiou]

Hi Marek,

I will abandon this patch and submit a new patch that is adapted from
do_div() and lib64.c of the Linux kernel. Does this sound okay to you?

Regards,
Che-Liang

On Thu, Sep 1, 2011 at 6:16 PM, Marek Vasut <marek.vasut at gmail.com> wrote:
> On Thursday, September 01, 2011 12:09:18 PM Che-liang Chiou wrote:
>> Hi,
>>
>> Thanks for the insightful comments. Here are my responses:
>>
>> * Why don't I implement the divider in C?
>> It is not because I think it's performance critical (I haven't
>> benchmarked it yet), but because I have a probably wrong impression
>> that the divider has to be written in assembly --- all dividers in
>> arch/arm/lib/ are written in ARM assembly. What is the policy here for
>> using assembly or C?
>
> No, C is just fine and is more generic. Those assembler versions are just
> optimized things, you don't need to be bothered by those.
>
>>
>> * When do we need a 64-bit divider?
>> In kernel code do_div() is used for various purposes. So I think it
>> should be quite often that we would need a 64-bit divider in U-Boot.
>
> Not much really ... and for the rare cases, we can do with do_div() as is.
>
>>
>> * Do we need a 64-64 bit divider?
>> do_div() defines 64-32 bit division semantics (dividend is 64-bit and
>> divisor is 32-bit), and this patch implements a 64-64 bit divider
>> (both dividend and divisor are 64-bit). I have to admit that I can't
>> think of scenarios or reasons to justify a 64-64 bit divider instead
>> of a 64-32 bit divider, except that a 64-64 bit divider is more
>> generic than a 64-32 bit one.
>
> So we don't need 64/64 divide at all.
>
>>
>> So I guess we can agree that a 64-bit divider is feature that is nice
>> to have, and we should decide:
>> * Do we need a 64-64 bit divider or a 64-32 bit one?
>
> 64-32 is do_div()
>
>> * Do we write it in C or assembly?
>
> C is OK.
>
>>
>> Depending on our decisions, I will rewrite (or abandon) this patch
>> accordingly.
>
> Look, I don't mean to be rough, but honestly. I see no use for this code. Adding
> code to anywhere so it'd just sit there is bad.
>
> Cheers
>
>>
>> Regards,
>> Che-Liang
>>
>> On Thu, Sep 1, 2011 at 4:03 AM, Wolfgang Denk <wd at denx.de> wrote:
>> > Dear Che-Liang Chiou,
>> >
>> > In message <1314787130-1043-1-git-send-email-clchiou at chromium.org> you
> wrote:
>> >> This patch adds a 64-64 bit divider that supports ARMv4 and above.
>> >
>> > To summarize the misc feedback:  Please explain in detail which
>> > problem you are trying to fix.  We see no need for this patch so far.
>> >
>> > Best regards,
>> >
>> > Wolfgang Denk
>> >
>> > --
>> > DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
>> > HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
>> > Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
>> > "Success covers a multitude of blunders."       - George Bernard Shaw
>