Groups > comp.lang.c++ > #81991

Re: faster "CRC"- / "FNV"-hashing

Newsgroups	comp.lang.c++
From	Branimir Maksimovic <branimir.maksimovic@icloud.com>
Subject	Re: faster "CRC"- / "FNV"-hashing
References	(6 earlier) <sk0u2a$ajc$1@dont-email.me> <wdT8J.185287$o45.132180@fx46.iad> <sk0vgf$6or$1@dont-email.me> <isin78Fpis6U1@mid.individual.net> <sk1abt$tn7$1@dont-email.me>
Message-ID	<dwW8J.64464$md6.15724@fx36.iad> (permalink)
Organization	usenet-news.net
Date	2021-10-11 12:56 +0000

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On 2021-10-11, David Brown <david.brown@hesbynett.no> wrote:
> On 11/10/2021 13:58, Bo Persson wrote:
>> On 2021-10-11 at 11:18, Bonita Montero wrote:
>>> Am 11.10.2021 um 11:11 schrieb Branimir Maksimovic:
>>>
>>>> ASM code is most efficient always and works as tested without
>>>> surprises :P
>>>
>>> ASM code can be faster in rare cases when you know everyting about
>>> your OoO-CPU, but in most cases the compiler generates better code.
>>> I've seen code from clang where you might think: there would be no
>>> ASM-programmer that knows all of these optimization-tricks.
>> 
>> In this case the asm code is supplied by Intel.
>> 
>> I bet they qualify for "you know everything about your OoO-CPU". :-)
>> 
>
> Well, kind of.  Intel as a whole probably knows most of what there is to
> know about Intel processors.  But Intel does not write code - people
> working at (or for) Intel write code, and there is absolutely no
> guarantee that the person or people who wrote the code know all about
> all of Intel's processors - never mind non-Intel x86 processors, or
> non-x86 processors, or any other device.  At best, you can probably be
> quite confident that the code is close to optimal if you run it on the
> same processor the assembly author used.
>
> How well it will run on the dozen other current Intel processor
> variations is another matter (by "dozen", I am ignoring devices that
> differ only in clock speed or core count, and ignoring older devices).
> How well it will run on AMD processors is also another matter.
>
> You write these routines in C (or C++), and you tune the optimisation.
> You compile with "-fmarch=native", or whatever flag your compiler has to
> get the fastest code for your particular processor.  You use compiler
> features for multi-versioning for target-specific optimisations, so that
> the compiler generates versions for different SIMD and other instruction
> set extensions, and picks the best version for the real cpu when the
> code starts up.  You use inline assembly or intrinsics for specific
> target versions if you are /sure/ your assembly works faster, and have
> measured it.
>
> General use of assembly language is something that comes /way/ down on
> the list when you are trying to get fast implementation of code.
Compiler at best can produce generic optimistic code that does not stand
a chance against dedicated human :P
ONly reason we do not program in assembler is because lerning curve is
steep :P

-- 

7-77-777
Evil Sinner!
with software, you repeat same experiment, expecting different results...

Thread

faster "CRC"- / "FNV"-hashing Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-10 18:51 +0200
  Re: faster "CRC"- / "FNV"-hashing "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-10-10 12:36 -0700
    Re: faster "CRC"- / "FNV"-hashing scott@slp53.sl.home (Scott Lurndal) - 2021-10-10 22:51 +0000
      Re: faster "CRC"- / "FNV"-hashing "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-10-12 13:47 -0700
    Re: faster "CRC"- / "FNV"-hashing Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-11 08:09 +0200
  Re: faster "CRC"- / "FNV"-hashing Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-11 05:23 +0000
    Re: faster "CRC"- / "FNV"-hashing Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-11 08:15 +0200
      Re: faster "CRC"- / "FNV"-hashing Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-11 06:29 +0000
        Re: faster "CRC"- / "FNV"-hashing Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-11 08:34 +0200
    Re: faster "CRC"- / "FNV"-hashing Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-11 08:27 +0200
      Re: faster "CRC"- / "FNV"-hashing Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-11 06:32 +0000
        Re: faster "CRC"- / "FNV"-hashing Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-11 08:33 +0200
          Re: faster "CRC"- / "FNV"-hashing Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-11 07:46 +0000
            Re: faster "CRC"- / "FNV"-hashing Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-11 10:53 +0200
              Re: faster "CRC"- / "FNV"-hashing Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-11 09:11 +0000
                Re: faster "CRC"- / "FNV"-hashing Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-11 11:18 +0200
                Re: faster "CRC"- / "FNV"-hashing Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-11 10:42 +0000
                Re: faster "CRC"- / "FNV"-hashing Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-11 13:03 +0200
                Re: faster "CRC"- / "FNV"-hashing Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-11 11:12 +0000
                Re: faster "CRC"- / "FNV"-hashing Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-11 13:44 +0200
                Re: faster "CRC"- / "FNV"-hashing Bo Persson <bo@bo-persson.se> - 2021-10-11 13:58 +0200
                Re: faster "CRC"- / "FNV"-hashing David Brown <david.brown@hesbynett.no> - 2021-10-11 14:23 +0200
                Re: faster "CRC"- / "FNV"-hashing Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-11 12:56 +0000
                Re: faster "CRC"- / "FNV"-hashing Bonita Montero <Bonita.Montero@gmail.com> - 2021-10-11 15:55 +0200
                Re: faster "CRC"- / "FNV"-hashing Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-11 16:55 +0000
                Re: faster "CRC"- / "FNV"-hashing RadicalRabbit@theburrow.co.uk - 2021-10-12 09:06 +0000
                Re: faster "CRC"- / "FNV"-hashing Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-12 11:01 +0000
                Re: faster "CRC"- / "FNV"-hashing RadicalRabbit@theburrow.co.uk - 2021-10-12 14:49 +0000
                Re: faster "CRC"- / "FNV"-hashing David Brown <david.brown@hesbynett.no> - 2021-10-11 17:19 +0200
                Re: faster "CRC"- / "FNV"-hashing Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-11 16:57 +0000
  Re: faster "CRC"- / "FNV"-hashing Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-11 05:41 +0000

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