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Failed to connect to MySQL: (1203) User howardkn already has more than 'max_user_connections' active connectionsPath: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Michael S Newsgroups: comp.lang.c Subject: Re: xxd -i vs DIY Was: C23 thoughts and opinions Date: Wed, 29 May 2024 09:21:09 +0300 Organization: A noiseless patient Spider Lines: 56 Message-ID: <20240529092109.0000246b@yahoo.com> References: <00297443-2fee-48d4-81a0-9ff6ae6481e4@gmail.com> <87msoh5uh6.fsf@nosuchdomain.example.com> <87y18047jk.fsf@nosuchdomain.example.com> <87msoe1xxo.fsf@nosuchdomain.example.com> <87ikz11osy.fsf@nosuchdomain.example.com> <20240528144118.00002012@yahoo.com> <20240528185624.00002494@yahoo.com> <20240528232315.00006a58@yahoo.com> <20240529004530.00005793@yahoo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Injection-Date: Wed, 29 May 2024 08:21:13 +0200 (CEST) Injection-Info: dont-email.me; posting-host="5312032778bda400147ee6d9907947d6"; logging-data="1091258"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19931sfDVbWZfnAmbJCFYYgr2FPZtyv8/I=" Cancel-Lock: sha1:f2+odmNjklZu2rT3LjaVCc9jG7U= X-Newsreader: Claws Mail 4.1.1 (GTK 3.24.34; x86_64-w64-mingw32) Bytes: 3605 On Wed, 29 May 2024 01:29:00 +0100 bart wrote: > On 28/05/2024 22:45, Michael S wrote: > > On Tue, 28 May 2024 23:23:15 +0300 > > Michael S wrote: > > > >> > >> Also, I think that random numbers are close to worst case for > >> branch predictor / loop length predictor in my inner loop. > >> Were I thinking about random case upfront, I'd code an inner loop > >> differently. I'd always copy 4 octets (comma would be stored in the > >> same table). After that I would update outptr by length taken from > >> additional table, similarly, but not identically to your method > >> below. > > > > That's what I had in mind: > > > > > unsigned char bin2dec[256][MAX_CHAR_PER_NUM+1]; // > > bin2dec[MAX_CHAR_PER_NUM] => length for (int i = 0; i < 256;++i) > > { > > Is this a comment that has wrapped? > > After fixing a few such line breaks, this runs at 3.6 seconds > compared with 4.1 seconds for the original. > > Although I don't quite understand the comments about branch > prediction. > > I think runtime is still primarily spent in I/O. > That's undoubtedly correct. But high branch mispredict rate still can add to total time. Suppose we have branch misprediction at the end of inner loop in 40% of the input bytes. On the processor that was running my original test (Intel Haswell at 4GHz) each mispredict cost ~15 clocks = 3.75 ns. 3.75ns * 0.4 * 100M = 150 msec I don't know how much it costs on your hardware since you didn't tell me what it is. But I am more intrigued by slowness on WSL. Did you compare native vs mounted file systems? > If I take the 1.9 second version, and remove the fwrite, then it runs > in 0.8 seconds. 0.7 of that is generating the text (366MB's worth, a > line at a time). > > In my language that part takes 0.9 seconds, which is a more typical > difference due to gcc's superior optimiser. > >