in reply to 4x faster now!
in thread Syntax Perl Version support $c = () = $a =~ /\./g

G'day h2,

"... and ended up with a 4x (!) speed improvement ..."

You might like to take a look at "perlperf - Perl Performance and Optimization Techniques" which discusses this, amongst other things, and includes benchmarks.

While y/// and s/// are not always interchangeable, when they can provide the same functionality, I've generally found y/// to be measurably faster than s///.

— Ken

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Re^2: 4x faster now!
by h2 (Beadle) on Jul 19, 2018 at 20:37 UTC
    I was lucky and discovered NTYProf quite early, so along with loop testing, I was able to get rid of major bottlenecks during development, which was and is kind of excellent. There's some optimization tricks I was not aware of in that perlperf page so those should help too, I've been using microtimers in loops which achieve the same result but I'll check out some of the other optimization tools, thanks. As noted above, sadly, the improvements once I made both test versions fully apples to apples turned out to be roughly 'only' 2.5x faster for tr and length vs regex. But equally obviously, anything that results in that big of a difference is worth understanding better, since usually you hope for 5, 10% improvements, not 250%.
[reply]
      "... roughly 'only' 2.5x faster ..."

      Interestingly, if you look at the benchmark timings in the perlperf page: 

      $ perl -E 'say 2040816.33/840336.13'
2.42857144557143

      [download]

      But don't read too much into that: I consider it more of a curiosity than anything else.

      "... anything that results in that big of a difference is worth understanding better ..."

      Someone else may have a much better answer regarding the inner workings of these. My understanding is that the SEARCH part of y///, e.g. the 'w' in 

      $ perl -E 'say "xwz" =~ y/w/y/r'
xyz

      [download]

      is handled at compile time; whereas the equivalent part of s///, e.g. the 'w' in 

      $ perl -E 'say "xwz" =~ s/w/y/r'
xyz

      [download]

      is handled at runtime. I couldn't tell you exactly what "handled" equates to; maybe another monk can chime in with a more complete answer.

      — Ken

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