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Re: poor performance while processing a file one byte a time

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On Thu, 20 Jan 2022 19:23:49 +0100
Arno Welzel <usenet@arnowelzel.de> wrote:
> > It works, but it is really slow (approximately 100x slower than the
> > original C code). I know that I should not expect much performance
> > from interpreted PHP code, but still - is there any trick I could
> > use to speed this up?  
> 
> By *not* using arrays.

That what I figured, but it did not find any way to not using them. :)

> Just use the string as it is:
> 
>     $len = strlen($buff);
>     $pos = 0;
>     while ($pos < $len) {
>       $result += ord($buff[$pos]);
>       $result &= 0xffff;
>       $pos++;
>     }

Yes, this is faster, but only by 10%. If I understand it right, the
"address a string like an array" is costly in PHP, and it must emulate
an array-like under the hood anyway. I was hoping there might be a
different approach that would be faster by at least an order of
magnitude... But if PHP doesn't have any faster construct for this kind
of things, I will live with it.

> However this may still be quite slow on larger files. Since it seems
> you want to create some kind of checksum based on the file content,
> you may want to use something else like hash_file(), sha1_file() or
> md5_file() and use the result of these calls instead processing the
> whole file content in a loop.

Sadly, that won't work. The kind of checksum I am computing is not
supported by PHP, hence why I do it byte by byte myself. Another
solution is to do it with my C code by system()-calling it from PHP,
but that's really ugly. At this point I'd rather stick with a slow, 100%
PHP solution.


Mateusz

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Thread

poor performance while processing a file one byte a time Mateusz Viste <mateusz@xyz.invalid> - 2022-01-20 15:16 +0100
  Re: poor performance while processing a file one byte a time John-Paul Stewart <jpstewart@personalprojects.net> - 2022-01-20 11:08 -0500
    Re: poor performance while processing a file one byte a time Mateusz Viste <mateusz@xyz.invalid> - 2022-01-20 17:23 +0100
      Re: poor performance while processing a file one byte a time John-Paul Stewart <jpstewart@personalprojects.net> - 2022-01-20 12:38 -0500
        Re: poor performance while processing a file one byte a time Mateusz Viste <mateusz@xyz.invalid> - 2022-01-20 19:49 +0100
    Re: poor performance while processing a file one byte a time Mateusz Viste <mateusz@xyz.invalid> - 2022-01-20 17:37 +0100
      Re: poor performance while processing a file one byte a time John-Paul Stewart <jpstewart@personalprojects.net> - 2022-01-20 12:41 -0500
        Re: poor performance while processing a file one byte a time Mateusz Viste <mateusz@xyz.invalid> - 2022-01-20 19:47 +0100
  Re: poor performance while processing a file one byte a time Arno Welzel <usenet@arnowelzel.de> - 2022-01-20 19:23 +0100
    Re: poor performance while processing a file one byte a time Mateusz Viste <mateusz@xyz.invalid> - 2022-01-20 19:45 +0100
      Re: poor performance while processing a file one byte a time Arno Welzel <usenet@arnowelzel.de> - 2022-01-20 20:27 +0100

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