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Re: [Patch] Optimize _BFSExecutor in regex

From: Tim Shen <timshen91 at gmail dot com>
To: Jonathan Wakely <jwakely dot gcc at gmail dot com>
Cc: "libstdc++" <libstdc++ at gcc dot gnu dot org>, gcc-patches <gcc-patches at gcc dot gnu dot org>
Date: Mon, 7 Oct 2013 17:14:12 -0400
Subject: Re: [Patch] Optimize _BFSExecutor in regex
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On Mon, Oct 7, 2013 at 1:28 PM, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
> std::memset() on about 125 bytes is not a big deal, I doubt it's
> significantly more expensive than the calculations to find the right
> bits and do the necessary masking for three elements.
> std::vector<bool> is a strange beast, remember.

Probably there could be bitwise operation?

I've test the 3 trues out of 1000 elements here :
https://gist.github.com/innocentim/6874889
In my machine, choosing "v.assign(v.size(), false);" cost 1.768s and
choosing the other cost 1.088s. When we push 7 elements, they cost
almost same time. When push more than that, v.assign() shall win.

I do this because I need to use _M_clear() in this patch :)

Anyway let's use v.assign().

Thanks!

-- 
Tim Shen

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Follow-Ups:
- Re: [Patch] Optimize _BFSExecutor in regex
  - From: Jonathan Wakely

References:
- [Patch] Optimize _BFSExecutor in regex
  - From: Tim Shen
- Re: [Patch] Optimize _BFSExecutor in regex
  - From: Jonathan Wakely
- Re: [Patch] Optimize _BFSExecutor in regex
  - From: Tim Shen
- Re: [Patch] Optimize _BFSExecutor in regex
  - From: Jonathan Wakely

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