February 2017
Intermediate to advanced
368 pages
8h 21m
Japanese
Content preview from Optimized C++ ―最適化、高速化のためのプログラミングテクニック
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67
4.2 文字列最適化の最初の試み
すべてが性能低下を引き起こす。
remove_ctrl()
は、小さな独立関数なので、関数を繰り返し呼び出すテストハーネスを作って、
最適化により性能が正確にどれだけ向上するかを計測することが可能だ。テストハーネスの構築と
計測については、
3
章で扱った。本書にあるテストハーネスのコードや他のコードは、ダウンロー
ド可能である（
http://www.guntheroth.com
）。
remove_ctrl()
を制御文字をいくつか含んだ
222
文字の引数文字列で反復呼び出しをする計時用
のテストプログラムを書いた。平均すると、各呼び出しで
24.8
マイクロ秒かかった。この数字自
体は、私の
PC
（
Intel i7
タブレット）、
OS
（
Windows 8.1
）、コンパイラ（
Visual Studio 2010
、
32
ビットリリースビルド）などに依存するので重要ではないが、性能改善を測定するためのベースラ
インとなる。次節以降で、
remove_ctrl()
関数の性能改善のための複数の最適化ステップをその結
果とともに述べる。
4.2.1
一時ストレージをなくすために変更文字列演算を使う
まず、
remove_ctrl()
の最適化を割り当ておよびコピー演算をなくすことから始める。例
4-2
は、
remove_ctrl()
の改良版で、多数の一時文字列オブジェクトを生成していた
5
行目の式を変更
連結代入演算子
+=
を使うように変更した。
例
4-2
remove_ctrl_mutating
()
：変更文字列演算子 ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.