Re: [PATCH/RFC] hash: Let gcc decide how to multiply

From: Rasmus Villemoes
Date: Tue Aug 26 2014 - 04:18:15 EST

David Miller <davem@xxxxxxxxxxxxx> writes:

> From: Daniel Borkmann <dborkman@xxxxxxxxxx>
> Date: Mon, 25 Aug 2014 14:58:37 +0200
>> On 08/25/2014 02:13 PM, Rasmus Villemoes wrote:
>>> A 9+ years old comment in hash_64 says that gcc can't optimize
>>> multiplication by GOLDEN_RATIO_PRIME_64. Well, compilers get smarter
>>> and CPUs get faster all the time, so it is perhaps about time to
>>> revisit that assumption.
>> Seems fine by me, but Cc'ing a couple of others (as those you have
>> Cc'ed haven't written that code :)). You might want to let your
>> changes go via Andrew's tree, too, perhaps ...
> You need to test the code generation for a cpu where the multiply
> instruction is more expensive than the shifts and adds.

Yes, I should, but I'm afraid I can't. I only have x86 hardware, and
even if I managed to set up some cross-compiler toolchain, I wouldn't
know what CPUs to target. So I was hoping someone else could test this
on appropriate platforms.

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